[PATCH net-next v4 0/3] Lockless netlink_lookup() with new concurrent hash table

[PATCH net-next v4 0/3] Lockless netlink_lookup() with new concurrent hash table

[Thomas Graf]

Netlink sockets are maintained in a hash table to allow efficient lookup
via the port ID for unicast messages. However, lookups currently require
a read lock to be taken. This series adds a new generic, resizable,
scalable, concurrent hash table based on the paper referenced in the first
patch. It then makes use of the new data type to implement lockless
netlink_lookup().

Patch 3/3 to convert nft_hash is included for reference but should be
merged via the netfilter tree. Inclusion in this series is to provide
context for the suggested API.

Against net-next since the initial user of the new hash table is in net/

Changes:
v3-v4
 - fixed wrong shift assignment placement as spotted by Nikolay Aleksandrov
 - reverted default size of nft_hash to 4 as requested by Patrick McHardy,
   default size for other hash tables remains at 64 if no hint is given
 - fixed copyright as requested by Patrick McHardy
v2-v3:
 - fixed typo in nft_hash_destroy() when passing rhashtable handle
v1-v2:
 - fixed traversal off-by-one as spotted by Tobias Klauser
 - removed unlikely() from BUG_ON() as spotted by Josh Triplett
 - new 3rd patch to convert nft_hash to rhashtable
 - make rhashtable_insert() return void
 - nl_sk_hash_lock must be a mutex
 - fixed wrong name of rht_shrink_below_30()
 - exported symbols rht_grow_above_75() and rht_shrink_below_30()
 - allow table freeing with RCU callback

Thomas Graf (3):
  lib: Resizable, Scalable, Concurrent Hash Table
  netlink: Convert netlink_lookup() to use RCU protected hash table
  nftables: Convert nft_hash to use generic rhashtable

 include/linux/rhashtable.h | 213 ++++++++++++
 lib/Kconfig.debug          |   8 +
 lib/Makefile               |   2 +-
 lib/rhashtable.c           | 797 +++++++++++++++++++++++++++++++++++++++++++++
 net/netfilter/nft_hash.c   | 292 +++--------------
 net/netlink/af_netlink.c   | 285 ++++++----------
 net/netlink/af_netlink.h   |  18 +-
 net/netlink/diag.c         |  11 +-
 8 files changed, 1192 insertions(+), 434 deletions(-)
 create mode 100644 include/linux/rhashtable.h
 create mode 100644 lib/rhashtable.c

-- 
1.9.3

[PATCH net-next v4 0/3] Lockless netlink_lookup() with new concurrent hash table

[Thomas Graf]

Netlink sockets are maintained in a hash table to allow efficient lookup
via the port ID for unicast messages. However, lookups currently require
a read lock to be taken. This series adds a new generic, resizable,
scalable, concurrent hash table based on the paper referenced in the first
patch. It then makes use of the new data type to implement lockless
netlink_lookup().

Patch 3/3 to convert nft_hash is included for reference but should be
merged via the netfilter tree. Inclusion in this series is to provide
context for the suggested API.

Against net-next since the initial user of the new hash table is in net/

Changes:
v3-v4
 - fixed wrong shift assignment placement as spotted by Nikolay Aleksandrov
 - reverted default size of nft_hash to 4 as requested by Patrick McHardy,
   default size for other hash tables remains at 64 if no hint is given
 - fixed copyright as requested by Patrick McHardy
v2-v3:
 - fixed typo in nft_hash_destroy() when passing rhashtable handle
v1-v2:
 - fixed traversal off-by-one as spotted by Tobias Klauser
 - removed unlikely() from BUG_ON() as spotted by Josh Triplett
 - new 3rd patch to convert nft_hash to rhashtable
 - make rhashtable_insert() return void
 - nl_sk_hash_lock must be a mutex
 - fixed wrong name of rht_shrink_below_30()
 - exported symbols rht_grow_above_75() and rht_shrink_below_30()
 - allow table freeing with RCU callback

Thomas Graf (3):
  lib: Resizable, Scalable, Concurrent Hash Table
  netlink: Convert netlink_lookup() to use RCU protected hash table
  nftables: Convert nft_hash to use generic rhashtable

 include/linux/rhashtable.h | 213 ++++++++++++
 lib/Kconfig.debug          |   8 +
 lib/Makefile               |   2 +-
 lib/rhashtable.c           | 797 +++++++++++++++++++++++++++++++++++++++++++++
 net/netfilter/nft_hash.c   | 292 +++--------------
 net/netlink/af_netlink.c   | 285 ++++++----------
 net/netlink/af_netlink.h   |  18 +-
 net/netlink/diag.c         |  11 +-
 8 files changed, 1192 insertions(+), 434 deletions(-)
 create mode 100644 include/linux/rhashtable.h
 create mode 100644 lib/rhashtable.c

-- 
1.9.3

[PATCH net-next 1/3] lib: Resizable, Scalable, Concurrent Hash Table

[Thomas Graf]

Generic implementation of a resizable, scalable, concurrent hash table
based on [0]. The implementation supports both, fixed size keys specified
via an offset and length, or arbitrary keys via own hash and compare
functions.

Lookups are lockless and protected as RCU read side critical sections.
Automatic growing/shrinking based on user configurable watermarks is
available while allowing concurrent lookups to take place.

Objects to be hashed must include a struct rhash_head. The reason for not
using the existing struct hlist_head is that the expansion and shrinking
will have two buckets point to a single entry which would lead in obscure
reverse chaining behaviour.

Code includes a boot selftest if CONFIG_TEST_RHASHTABLE is defined.

[0] https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf

Signed-off-by: Thomas Graf <tgraf@suug.ch>
---
 include/linux/rhashtable.h | 213 ++++++++++++
 lib/Kconfig.debug          |   8 +
 lib/Makefile               |   2 +-
 lib/rhashtable.c           | 797 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 1019 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/rhashtable.h
 create mode 100644 lib/rhashtable.c

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
new file mode 100644
index 0000000..9cda293
--- /dev/null
+++ b/include/linux/rhashtable.h
@@ -0,0 +1,213 @@
+/*
+ * Resizable, Scalable, Concurrent Hash Table
+ *
+ * Copyright (c) 2014 Thomas Graf <tgraf@suug.ch>
+ * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
+ *
+ * Based on the following paper by Josh Triplett, Paul E. McKenney
+ * and Jonathan Walpole:
+ * https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf
+ *
+ * Code partially derived from nft_hash
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef _LINUX_RHASHTABLE_H
+#define _LINUX_RHASHTABLE_H
+
+#include <linux/rculist.h>
+
+struct rhash_head {
+	struct rhash_head		*next;
+};
+
+#define INIT_HASH_HEAD(ptr) ((ptr)->next = NULL)
+
+struct bucket_table {
+	size_t				size;
+	struct rhash_head __rcu		*buckets[];
+};
+
+typedef u32 (*rht_hashfn_t)(const void *data, u32 len, u32 seed);
+typedef u32 (*rht_obj_hashfn_t)(const void *data, u32 seed);
+
+struct rhashtable;
+
+/**
+ * struct rhashtable_params - Hash table construction parameters
+ * @nelem_hint: Hint on number of elements, should be 75% of desired size
+ * @key_len: Length of key
+ * @key_offset: Offset of key in struct to be hashed
+ * @head_offset: Offset of rhash_head in struct to be hashed
+ * @hash_rnd: Seed to use while hashing
+ * @max_shift: Maximum number of shifts while expanding
+ * @hashfn: Function to hash key
+ * @obj_hashfn: Function to hash object
+ * @grow_decision: If defined, may return true if table should expand
+ * @shrink_decision: If defined, may return true if table should shrink
+ * @mutex_is_held: Must return true if protecting mutex is held
+ */
+struct rhashtable_params {
+	size_t			nelem_hint;
+	size_t			key_len;
+	size_t			key_offset;
+	size_t			head_offset;
+	u32			hash_rnd;
+	size_t			max_shift;
+	rht_hashfn_t		hashfn;
+	rht_obj_hashfn_t	obj_hashfn;
+	bool			(*grow_decision)(const struct rhashtable *ht,
+						 size_t new_size);
+	bool			(*shrink_decision)(const struct rhashtable *ht,
+						   size_t new_size);
+	int			(*mutex_is_held)(void);
+};
+
+/**
+ * struct rhashtable - Hash table handle
+ * @tbl: Bucket table
+ * @nelems: Number of elements in table
+ * @shift: Current size (1 << shift)
+ * @p: Configuration parameters
+ */
+struct rhashtable {
+	struct bucket_table __rcu	*tbl;
+	size_t				nelems;
+	size_t				shift;
+	struct rhashtable_params	p;
+};
+
+#ifdef CONFIG_PROVE_LOCKING
+int lockdep_rht_mutex_is_held(const struct rhashtable *ht);
+#else
+static inline int lockdep_rht_mutex_is_held(const struct rhashtable *ht)
+{
+	return 1;
+}
+#endif /* CONFIG_PROVE_LOCKING */
+
+int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params);
+
+u32 rhashtable_hashfn(const struct rhashtable *ht, const void *key, u32 len);
+u32 rhashtable_obj_hashfn(const struct rhashtable *ht, void *ptr);
+
+void rhashtable_insert(struct rhashtable *ht, struct rhash_head *node, gfp_t);
+bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *node, gfp_t);
+void rhashtable_remove_pprev(struct rhashtable *ht, struct rhash_head *obj,
+			     struct rhash_head **pprev, gfp_t flags);
+
+bool rht_grow_above_75(const struct rhashtable *ht, size_t new_size);
+bool rht_shrink_below_30(const struct rhashtable *ht, size_t new_size);
+
+int rhashtable_expand(struct rhashtable *ht, gfp_t flags);
+int rhashtable_shrink(struct rhashtable *ht, gfp_t flags);
+
+void *rhashtable_lookup(const struct rhashtable *ht, const void *key);
+void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash,
+				bool (*compare)(void *, void *), void *arg);
+
+void rhashtable_destroy(const struct rhashtable *ht);
+
+#define rht_dereference(p, ht) \
+	rcu_dereference_protected(p, lockdep_rht_mutex_is_held(ht))
+
+#define rht_dereference_rcu(p, ht) \
+	rcu_dereference_check(p, lockdep_rht_mutex_is_held(ht))
+
+/* Internal, use rht_obj() instead */
+#define rht_entry(ptr, type, member) container_of(ptr, type, member)
+#define rht_entry_safe(ptr, type, member) \
+({ \
+	typeof(ptr) __ptr = (ptr); \
+	   __ptr ? rht_entry(__ptr, type, member) : NULL; \
+})
+#define rht_entry_safe_rcu(ptr, type, member) \
+({ \
+	typeof(*ptr) __rcu *__ptr = (typeof(*ptr) __rcu __force *)ptr; \
+	__ptr ? container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member) : NULL; \
+})
+
+#define rht_next_entry_safe(pos, ht, member) \
+({ \
+	pos ? rht_entry_safe(rht_dereference((pos)->member.next, ht), \
+			     typeof(*(pos)), member) : NULL; \
+})
+
+/**
+ * rht_for_each - iterate over hash chain
+ * @pos:	&struct rhash_head to use as a loop cursor.
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @ht:		pointer to your struct rhashtable
+ */
+#define rht_for_each(pos, head, ht) \
+	for (pos = rht_dereference(head, ht); \
+	     pos; \
+	     pos = rht_dereference((pos)->next, ht))
+
+/**
+ * rht_for_each_entry - iterate over hash chain of given type
+ * @pos:	type * to use as a loop cursor.
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @ht:		pointer to your struct rhashtable
+ * @member:	name of the rhash_head within the hashable struct.
+ */
+#define rht_for_each_entry(pos, head, ht, member) \
+	for (pos = rht_entry_safe(rht_dereference(head, ht), \
+				   typeof(*(pos)), member); \
+	     pos; \
+	     pos = rht_next_entry_safe(pos, ht, member))
+
+/**
+ * rht_for_each_entry_safe - safely iterate over hash chain of given type
+ * @pos:	type * to use as a loop cursor.
+ * @n:		type * to use for temporary next object storage
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @ht:		pointer to your struct rhashtable
+ * @member:	name of the rhash_head within the hashable struct.
+ *
+ * This hash chain list-traversal primitive allows for the looped code to
+ * remove the loop cursor from the list.
+ */
+#define rht_for_each_entry_safe(pos, n, head, ht, member)		\
+	for (pos = rht_entry_safe(rht_dereference(head, ht), \
+				  typeof(*(pos)), member), \
+	     n = rht_next_entry_safe(pos, ht, member); \
+	     pos; \
+	     pos = n, \
+	     n = rht_next_entry_safe(pos, ht, member))
+
+/**
+ * rht_for_each_rcu - iterate over rcu hash chain
+ * @pos:	&struct rhash_head to use as a loop cursor.
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @ht:		pointer to your struct rhashtable
+ *
+ * This hash chain list-traversal primitive may safely run concurrently with
+ * the _rcu fkht mutation primitives such as rht_insert() as long as the
+ * traversal is guarded by rcu_read_lock().
+ */
+#define rht_for_each_rcu(pos, head, ht) \
+	for (pos = rht_dereference_rcu(head, ht); \
+	     pos; \
+	     pos = rht_dereference_rcu((pos)->next, ht))
+
+/**
+ * rht_for_each_entry_rcu - iterate over rcu hash chain of given type
+ * @pos:	type * to use as a loop cursor.
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @member:	name of the rhash_head within the hashable struct.
+ *
+ * This hash chain list-traversal primitive may safely run concurrently with
+ * the _rcu fkht mutation primitives such as rht_insert() as long as the
+ * traversal is guarded by rcu_read_lock().
+ */
+#define rht_for_each_entry_rcu(pos, head, member) \
+	for (pos = rht_entry_safe_rcu(head, typeof(*(pos)), member); \
+	     pos; \
+	     pos = rht_entry_safe_rcu((pos)->member.next, \
+				      typeof(*(pos)), member))
+
+#endif /* _LINUX_RHASHTABLE_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 7a638aa..f11a2e8 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1550,6 +1550,14 @@ config TEST_STRING_HELPERS
 config TEST_KSTRTOX
 	tristate "Test kstrto*() family of functions at runtime"
 
+config TEST_RHASHTABLE
+	bool "Perform selftest on resizable hash table"
+	default n
+	help
+	  Enable this option to test the rhashtable functions at boot.
+
+	  If unsure, say N.
+
 endmenu # runtime tests
 
 config PROVIDE_OHCI1394_DMA_INIT
diff --git a/lib/Makefile b/lib/Makefile
index ba967a1..fd248e4 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -26,7 +26,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
 	 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
 	 gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \
 	 bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \
-	 percpu-refcount.o percpu_ida.o hash.o
+	 percpu-refcount.o percpu_ida.o hash.o rhashtable.o
 obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += kstrtox.o
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
new file mode 100644
index 0000000..e6940cf
--- /dev/null
+++ b/lib/rhashtable.c
@@ -0,0 +1,797 @@
+/*
+ * Resizable, Scalable, Concurrent Hash Table
+ *
+ * Copyright (c) 2014 Thomas Graf <tgraf@suug.ch>
+ * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
+ *
+ * Based on the following paper:
+ * https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf
+ *
+ * Code partially derived from nft_hash
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/log2.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+#include <linux/hash.h>
+#include <linux/random.h>
+#include <linux/rhashtable.h>
+#include <linux/log2.h>
+
+#define HASH_DEFAULT_SIZE	64UL
+#define HASH_MIN_SIZE		4UL
+
+#define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
+
+#ifdef CONFIG_PROVE_LOCKING
+int lockdep_rht_mutex_is_held(const struct rhashtable *ht)
+{
+	return ht->p.mutex_is_held();
+}
+EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
+#endif
+
+/**
+ * rht_obj - cast hash head to outer object
+ * @ht:		hash table
+ * @he:		hashed node
+ */
+void *rht_obj(const struct rhashtable *ht, const struct rhash_head *he)
+{
+	return (void *) he - ht->p.head_offset;
+}
+EXPORT_SYMBOL_GPL(rht_obj);
+
+static u32 __hashfn(const struct rhashtable *ht, const void *key,
+		      u32 len, u32 hsize)
+{
+	u32 h;
+
+	h = ht->p.hashfn(key, len, ht->p.hash_rnd);
+
+	return h & (hsize - 1);
+}
+
+/**
+ * rhashtable_hashfn - compute hash for key of given length
+ * @ht:		hash table to compuate for
+ * @key:	pointer to key
+ * @len:	length of key
+ *
+ * Computes the hash value using the hash function provided in the 'hashfn'
+ * of struct rhashtable_params. The returned value is guaranteed to be
+ * smaller than the number of buckets in the hash table.
+ */
+u32 rhashtable_hashfn(const struct rhashtable *ht, const void *key, u32 len)
+{
+	struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+
+	return __hashfn(ht, key, len, tbl->size);
+}
+EXPORT_SYMBOL_GPL(rhashtable_hashfn);
+
+static u32 obj_hashfn(const struct rhashtable *ht, const void *ptr, u32 hsize)
+{
+	if (unlikely(!ht->p.key_len)) {
+		u32 h;
+
+		h = ht->p.obj_hashfn(ptr, ht->p.hash_rnd);
+
+		return h & (hsize - 1);
+	}
+
+	return __hashfn(ht, ptr + ht->p.key_offset, ht->p.key_len, hsize);
+}
+
+/**
+ * rhashtable_obj_hashfn - compute hash for hashed object
+ * @ht:		hash table to compuate for
+ * @ptr:	pointer to hashed object
+ *
+ * Computes the hash value using the hash function `hashfn` respectively
+ * 'obj_hashfn' depending on whether the hash table is set up to work with
+ * a fixed length key. The returned value is guaranteed to be smaller than
+ * the number of buckets in the hash table.
+ */
+u32 rhashtable_obj_hashfn(const struct rhashtable *ht, void *ptr)
+{
+	struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+
+	return obj_hashfn(ht, ptr, tbl->size);
+}
+EXPORT_SYMBOL_GPL(rhashtable_obj_hashfn);
+
+static u32 head_hashfn(const struct rhashtable *ht,
+		       const struct rhash_head *he, u32 hsize)
+{
+	return obj_hashfn(ht, rht_obj(ht, he), hsize);
+}
+
+static struct bucket_table *bucket_table_alloc(size_t nbuckets, gfp_t flags)
+{
+	struct bucket_table *tbl;
+	size_t size;
+
+	size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
+	tbl = kzalloc(size, flags);
+	if (tbl == NULL)
+		tbl = vzalloc(size);
+
+	if (tbl == NULL)
+		return NULL;
+
+	tbl->size = nbuckets;
+
+	return tbl;
+}
+
+static void bucket_table_free(const struct bucket_table *tbl)
+{
+	kvfree(tbl);
+}
+
+/**
+ * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
+ * @ht:		hash table
+ * @new_size:	new table size
+ */
+bool rht_grow_above_75(const struct rhashtable *ht, size_t new_size)
+{
+	/* Expand table when exceeding 75% load */
+	return ht->nelems > (new_size / 4 * 3);
+}
+EXPORT_SYMBOL_GPL(rht_grow_above_75);
+
+/**
+ * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
+ * @ht:		hash table
+ * @new_size:	new table size
+ */
+bool rht_shrink_below_30(const struct rhashtable *ht, size_t new_size)
+{
+	/* Shrink table beneath 30% load */
+	return ht->nelems < (new_size * 3 / 10);
+}
+EXPORT_SYMBOL_GPL(rht_shrink_below_30);
+
+static void hashtable_chain_unzip(const struct rhashtable *ht,
+				  const struct bucket_table *new_tbl,
+				  struct bucket_table *old_tbl, size_t n)
+{
+	struct rhash_head *he, *p, *next;
+	unsigned int h;
+
+	/* Old bucket empty, no work needed. */
+	p = rht_dereference(old_tbl->buckets[n], ht);
+	if (!p)
+		return;
+
+	/* Advance the old bucket pointer one or more times until it
+	 * reaches a node that doesn't hash to the same bucket as the
+	 * previous node p. Call the previous node p;
+	 */
+	h = head_hashfn(ht, p, new_tbl->size);
+	rht_for_each(he, p->next, ht) {
+		if (head_hashfn(ht, he, new_tbl->size) != h)
+			break;
+		p = he;
+	}
+	RCU_INIT_POINTER(old_tbl->buckets[n], p->next);
+
+	/* Find the subsequent node which does hash to the same
+	 * bucket as node P, or NULL if no such node exists.
+	 */
+	next = NULL;
+	if (he) {
+		rht_for_each(he, he->next, ht) {
+			if (head_hashfn(ht, he, new_tbl->size) == h) {
+				next = he;
+				break;
+			}
+		}
+	}
+
+	/* Set p's next pointer to that subsequent node pointer,
+	 * bypassing the nodes which do not hash to p's bucket
+	 */
+	RCU_INIT_POINTER(p->next, next);
+}
+
+/**
+ * rhashtable_expand - Expand hash table while allowing concurrent lookups
+ * @ht:		the hash table to expand
+ * @flags:	allocation flags
+ *
+ * A secondary bucket array is allocated and the hash entries are migrated
+ * while keeping them on both lists until the end of the RCU grace period.
+ *
+ * This function may only be called in a context where it is safe to call
+ * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
+ *
+ * The caller must ensure that no concurrent table mutations take place.
+ * It is however valid to have concurrent lookups if they are RCU protected.
+ */
+int rhashtable_expand(struct rhashtable *ht, gfp_t flags)
+{
+	struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
+	struct rhash_head *he;
+	unsigned int i, h;
+	bool complete;
+
+	ASSERT_RHT_MUTEX(ht);
+
+	if (ht->p.max_shift && ht->shift >= ht->p.max_shift)
+		return 0;
+
+	new_tbl = bucket_table_alloc(old_tbl->size * 2, flags);
+	if (new_tbl == NULL)
+		return -ENOMEM;
+
+	ht->shift++;
+
+	/* For each new bucket, search the corresponding old bucket
+	 * for the first entry that hashes to the new bucket, and
+	 * link the new bucket to that entry. Since all the entries
+	 * which will end up in the new bucket appear in the same
+	 * old bucket, this constructs an entirely valid new hash
+	 * table, but with multiple buckets "zipped" together into a
+	 * single imprecise chain.
+	 */
+	for (i = 0; i < new_tbl->size; i++) {
+		h = i & (old_tbl->size - 1);
+		rht_for_each(he, old_tbl->buckets[h], ht) {
+			if (head_hashfn(ht, he, new_tbl->size) == i) {
+				RCU_INIT_POINTER(new_tbl->buckets[i], he);
+				break;
+			}
+		}
+	}
+
+	/* Publish the new table pointer. Lookups may now traverse
+	 * the new table, but they will not benefit from any
+	 * additional efficiency until later steps unzip the buckets.
+	 */
+	rcu_assign_pointer(ht->tbl, new_tbl);
+
+	/* Unzip interleaved hash chains */
+	do {
+		/* Wait for readers. All new readers will see the new
+		 * table, and thus no references to the old table will
+		 * remain.
+		 */
+		synchronize_rcu();
+
+		/* For each bucket in the old table (each of which
+		 * contains items from multiple buckets of the new
+		 * table): ...
+		 */
+		complete = true;
+		for (i = 0; i < old_tbl->size; i++) {
+			hashtable_chain_unzip(ht, new_tbl, old_tbl, i);
+			if (old_tbl->buckets[i] != NULL)
+				complete = false;
+		}
+	} while (!complete);
+
+	bucket_table_free(old_tbl);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_expand);
+
+/**
+ * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
+ * @ht:		the hash table to shrink
+ * @flags:	allocation flags
+ *
+ * This function may only be called in a context where it is safe to call
+ * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
+ *
+ * The caller must ensure that no concurrent table mutations take place.
+ * It is however valid to have concurrent lookups if they are RCU protected.
+ */
+int rhashtable_shrink(struct rhashtable *ht, gfp_t flags)
+{
+	struct bucket_table *ntbl, *tbl = rht_dereference(ht->tbl, ht);
+	struct rhash_head __rcu **pprev;
+	unsigned int i;
+
+	ASSERT_RHT_MUTEX(ht);
+
+	if (tbl->size <= HASH_MIN_SIZE)
+		return 0;
+
+	ntbl = bucket_table_alloc(tbl->size / 2, flags);
+	if (ntbl == NULL)
+		return -ENOMEM;
+
+	ht->shift--;
+
+	/* Link each bucket in the new table to the first bucket
+	 * in the old table that contains entries which will hash
+	 * to the new bucket.
+	 */
+	for (i = 0; i < ntbl->size; i++) {
+		ntbl->buckets[i] = tbl->buckets[i];
+
+		/* Link each bucket in the new table to the first bucket
+		 * in the old table that contains entries which will hash
+		 * to the new bucket.
+		 */
+		for (pprev = &ntbl->buckets[i]; *pprev != NULL;
+		     pprev = &rht_dereference(*pprev, ht)->next)
+			;
+		RCU_INIT_POINTER(*pprev, tbl->buckets[i + ntbl->size]);
+	}
+
+	/* Publish the new, valid hash table */
+	rcu_assign_pointer(ht->tbl, ntbl);
+
+	/* Wait for readers. No new readers will have references to the
+	 * old hash table.
+	 */
+	synchronize_rcu();
+
+	bucket_table_free(tbl);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_shrink);
+
+/**
+ * rhashtable_insert - insert object into hash hash table
+ * @ht:		hash table
+ * @obj:	pointer to hash head inside object
+ * @flags:	allocation flags (table expansion)
+ *
+ * Will automatically grow the table via rhashtable_expand() if the the
+ * grow_decision function specified at rhashtable_init() returns true.
+ *
+ * The caller must ensure that no concurrent table mutations occur. It is
+ * however valid to have concurrent lookups if they are RCU protected.
+ */
+void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
+		       gfp_t flags)
+{
+	struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+	u32 hash;
+
+	ASSERT_RHT_MUTEX(ht);
+
+	hash = head_hashfn(ht, obj, tbl->size);
+	RCU_INIT_POINTER(obj->next, tbl->buckets[hash]);
+	rcu_assign_pointer(tbl->buckets[hash], obj);
+	ht->nelems++;
+
+	if (ht->p.grow_decision && ht->p.grow_decision(ht, tbl->size))
+		rhashtable_expand(ht, flags);
+}
+EXPORT_SYMBOL_GPL(rhashtable_insert);
+
+/**
+ * rhashtable_remove_pprev - remove object from hash table given previous element
+ * @ht:		hash table
+ * @obj:	pointer to hash head inside object
+ * @pprev:	pointer to previous element
+ * @flags:	allocation flags (table expansion)
+ *
+ * Identical to rhashtable_remove() but caller is alreayd aware of the element
+ * in front of the element to be deleted. This is in particular useful for
+ * deletion when combined with walking or lookup.
+ */
+void rhashtable_remove_pprev(struct rhashtable *ht, struct rhash_head *obj,
+			     struct rhash_head **pprev, gfp_t flags)
+{
+	struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+	ASSERT_RHT_MUTEX(ht);
+
+	RCU_INIT_POINTER(*pprev, obj->next);
+	ht->nelems--;
+
+	if (ht->p.shrink_decision &&
+	    ht->p.shrink_decision(ht, tbl->size))
+		rhashtable_shrink(ht, flags);
+}
+EXPORT_SYMBOL_GPL(rhashtable_remove_pprev);
+
+/**
+ * rhashtable_remove - remove object from hash table
+ * @ht:		hash table
+ * @obj:	pointer to hash head inside object
+ * @flags:	allocation flags (table expansion)
+ *
+ * Since the hash chain is single linked, the removal operation needs to
+ * walk the bucket chain upon removal. The removal operation is thus
+ * considerable slow if the hash table is not correctly sized.
+ *
+ * Will automatically shrink the table via rhashtable_expand() if the the
+ * shrink_decision function specified at rhashtable_init() returns true.
+ *
+ * The caller must ensure that no concurrent table mutations occur. It is
+ * however valid to have concurrent lookups if they are RCU protected.
+ */
+bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj,
+		       gfp_t flags)
+{
+	struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+	struct rhash_head __rcu **pprev;
+	struct rhash_head *he;
+	u32 h;
+
+	ASSERT_RHT_MUTEX(ht);
+
+	h = head_hashfn(ht, obj, tbl->size);
+
+	pprev = &tbl->buckets[h];
+	rht_for_each(he, tbl->buckets[h], ht) {
+		if (he != obj) {
+			pprev = &he->next;
+			continue;
+		}
+
+		rhashtable_remove_pprev(ht, he, pprev, flags);
+		return true;
+	}
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(rhashtable_remove);
+
+/**
+ * rhashtable_lookup - lookup key in hash table
+ * @ht:		hash table
+ * @key:	pointer to key
+ *
+ * Computes the hash value for the key and traverses the bucket chain looking
+ * for a entry with an identical key. The first matching entry is returned.
+ *
+ * This lookup function may only be used for fixed key hash table (key_len
+ * paramter set). It will BUG() if used inappropriately.
+ *
+ * Lookups may occur in parallel with hash mutations as long as the lookup is
+ * guarded by rcu_read_lock(). The caller must take care of this.
+ */
+void *rhashtable_lookup(const struct rhashtable *ht, const void *key)
+{
+	const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+	struct rhash_head *he;
+	u32 h;
+
+	BUG_ON(!ht->p.key_len);
+
+	h = __hashfn(ht, key, ht->p.key_len, tbl->size);
+	rht_for_each_rcu(he, tbl->buckets[h], ht) {
+		if (memcmp(rht_obj(ht, he) + ht->p.key_offset, key,
+			   ht->p.key_len))
+			continue;
+		return (void *) he - ht->p.head_offset;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(rhashtable_lookup);
+
+/**
+ * rhashtable_lookup_compare - search hash table with compare function
+ * @ht:		hash table
+ * @hash:	hash value of desired entry
+ * @compare:	compare function, must return true on match
+ * @arg:	argument passed on to compare function
+ *
+ * Traverses the bucket chain behind the provided hash value and calls the
+ * specified compare function for each entry.
+ *
+ * Lookups may occur in parallel with hash mutations as long as the lookup is
+ * guarded by rcu_read_lock(). The caller must take care of this.
+ *
+ * Returns the first entry on which the compare function returned true.
+ */
+void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash,
+				bool (*compare)(void *, void *), void *arg)
+{
+	const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+	struct rhash_head *he;
+
+	if (unlikely(hash >= tbl->size))
+		return NULL;
+
+	rht_for_each_rcu(he, tbl->buckets[hash], ht) {
+		if (!compare(rht_obj(ht, he), arg))
+			continue;
+		return (void *) he - ht->p.head_offset;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(rhashtable_lookup_compare);
+
+static size_t rounded_hashtable_size(unsigned int nelem)
+{
+	return max(roundup_pow_of_two(nelem * 4 / 3), HASH_MIN_SIZE);
+}
+
+/**
+ * rhashtable_init - initialize a new hash table
+ * @ht:		hash table to be initialized
+ * @params:	configuration parameters
+ *
+ * Initializes a new hash table based on the provided configuration
+ * parameters. A table can be configured either with a variable or
+ * fixed length key:
+ *
+ * Configuration Example 1: Fixed length keys
+ * struct test_obj {
+ *	int			key;
+ *	void *			my_member;
+ *	struct rhash_head	node;
+ * };
+ *
+ * struct rhashtable_params params = {
+ *	.head_offset = offsetof(struct test_obj, node),
+ *	.key_offset = offsetof(struct test_obj, key),
+ *	.key_len = sizeof(int),
+ *	.hashfn = arch_fast_hash,
+ *	.mutex_is_held = &my_mutex_is_held,
+ * };
+ *
+ * Configuration Example 2: Variable length keys
+ * struct test_obj {
+ *	[...]
+ *	struct rhash_head	node;
+ * };
+ *
+ * u32 my_hash_fn(const void *data, u32 seed)
+ * {
+ *	struct test_obj *obj = data;
+ *
+ *	return [... hash ...];
+ * }
+ *
+ * struct rhashtable_params params = {
+ *	.head_offset = offsetof(struct test_obj, node),
+ *	.hashfn = arch_fast_hash,
+ *	.obj_hashfn = my_hash_fn,
+ *	.mutex_is_held = &my_mutex_is_held,
+ * };
+ */
+int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
+{
+	struct bucket_table *tbl;
+	size_t size;
+
+	size = HASH_DEFAULT_SIZE;
+
+	if ((params->key_len && !params->hashfn) ||
+	    (!params->key_len && !params->obj_hashfn))
+		return -EINVAL;
+
+	if (params->nelem_hint)
+		size = rounded_hashtable_size(params->nelem_hint);
+
+	tbl = bucket_table_alloc(size, GFP_KERNEL);
+	if (tbl == NULL)
+		return -ENOMEM;
+
+	memset(ht, 0, sizeof(*ht));
+	ht->shift = ilog2(tbl->size);
+	memcpy(&ht->p, params, sizeof(*params));
+	RCU_INIT_POINTER(ht->tbl, tbl);
+
+	if (!ht->p.hash_rnd)
+		get_random_bytes(&ht->p.hash_rnd, sizeof(ht->p.hash_rnd));
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_init);
+
+/**
+ * rhashtable_destroy - destroy hash table
+ * @ht:		the hash table to destroy
+ *
+ * Frees the bucket array.
+ */
+void rhashtable_destroy(const struct rhashtable *ht)
+{
+	const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+	bucket_table_free(tbl);
+}
+EXPORT_SYMBOL_GPL(rhashtable_destroy);
+
+/**************************************************************************
+ * Self Test
+ **************************************************************************/
+
+#ifdef CONFIG_TEST_RHASHTABLE
+
+#define TEST_HT_SIZE	8
+#define TEST_ENTRIES	2048
+#define TEST_PTR	((void *) 0xdeadbeef)
+#define TEST_NEXPANDS	4
+
+static int test_mutex_is_held(void)
+{
+	return 1;
+}
+
+struct test_obj {
+	void			*ptr;
+	int			value;
+	struct rhash_head	node;
+};
+
+static int __init test_rht_lookup(struct rhashtable *ht)
+{
+	unsigned int i;
+
+	for (i = 0; i < TEST_ENTRIES * 2; i++) {
+		struct test_obj *obj;
+		bool expected = !(i % 2);
+		u32 key = i;
+
+		obj = rhashtable_lookup(ht, &key);
+
+		if (expected && !obj) {
+			pr_warn("Test failed: Could not find key %u\n", key);
+			return -ENOENT;
+		} else if (!expected && obj) {
+			pr_warn("Test failed: Unexpected entry found for key %u\n",
+				key);
+			return -EEXIST;
+		} else if (expected && obj) {
+			if (obj->ptr != TEST_PTR || obj->value != i) {
+				pr_warn("Test failed: Lookup value mismatch %p!=%p, %u!=%u\n",
+					obj->ptr, TEST_PTR, obj->value, i);
+				return -EINVAL;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static void test_bucket_stats(struct rhashtable *ht,
+				     struct bucket_table *tbl,
+				     bool quiet)
+{
+	unsigned int cnt, i, total = 0;
+	struct test_obj *obj;
+
+	for (i = 0; i < tbl->size; i++) {
+		cnt = 0;
+
+		if (!quiet)
+			pr_info(" [%#4x/%zu]", i, tbl->size);
+
+		rht_for_each_entry_rcu(obj, tbl->buckets[i], node) {
+			cnt++;
+			total++;
+			if (!quiet)
+				pr_cont(" [%p],", obj);
+		}
+
+		if (!quiet)
+			pr_cont("\n  [%#x] first element: %p, chain length: %u\n",
+				i, tbl->buckets[i], cnt);
+	}
+
+	pr_info("  Traversal complete: counted=%u, nelems=%zu, entries=%d\n",
+		total, ht->nelems, TEST_ENTRIES);
+}
+
+static int __init test_rhashtable(struct rhashtable *ht)
+{
+	struct bucket_table *tbl;
+	struct test_obj *obj, *next;
+	int err;
+	unsigned int i;
+
+	/*
+	 * Insertion Test:
+	 * Insert TEST_ENTRIES into table with all keys even numbers
+	 */
+	pr_info("  Adding %d keys\n", TEST_ENTRIES);
+	for (i = 0; i < TEST_ENTRIES; i++) {
+		struct test_obj *obj;
+
+		obj = kzalloc(sizeof(*obj), GFP_KERNEL);
+		if (!obj) {
+			err = -ENOMEM;
+			goto error;
+		}
+
+		obj->ptr = TEST_PTR;
+		obj->value = i * 2;
+
+		rhashtable_insert(ht, &obj->node, GFP_KERNEL);
+	}
+
+	rcu_read_lock();
+	tbl = rht_dereference_rcu(ht->tbl, ht);
+	test_bucket_stats(ht, tbl, true);
+	test_rht_lookup(ht);
+	rcu_read_unlock();
+
+	for (i = 0; i < TEST_NEXPANDS; i++) {
+		pr_info("  Table expansion iteration %u...\n", i);
+		rhashtable_expand(ht, GFP_KERNEL);
+
+		rcu_read_lock();
+		pr_info("  Verifying lookups...\n");
+		test_rht_lookup(ht);
+		rcu_read_unlock();
+	}
+
+	for (i = 0; i < TEST_NEXPANDS; i++) {
+		pr_info("  Table shrinkage iteration %u...\n", i);
+		rhashtable_shrink(ht, GFP_KERNEL);
+
+		rcu_read_lock();
+		pr_info("  Verifying lookups...\n");
+		test_rht_lookup(ht);
+		rcu_read_unlock();
+	}
+
+	pr_info("  Deleting %d keys\n", TEST_ENTRIES);
+	for (i = 0; i < TEST_ENTRIES; i++) {
+		u32 key = i * 2;
+
+		obj = rhashtable_lookup(ht, &key);
+		BUG_ON(!obj);
+
+		rhashtable_remove(ht, &obj->node, GFP_KERNEL);
+		kfree(obj);
+	}
+
+	return 0;
+
+error:
+	tbl = rht_dereference_rcu(ht->tbl, ht);
+	for (i = 0; i < tbl->size; i++)
+		rht_for_each_entry_safe(obj, next, tbl->buckets[i], ht, node)
+			kfree(obj);
+
+	return err;
+}
+
+static int __init test_rht_init(void)
+{
+	struct rhashtable ht;
+	struct rhashtable_params params = {
+		.nelem_hint = TEST_HT_SIZE,
+		.head_offset = offsetof(struct test_obj, node),
+		.key_offset = offsetof(struct test_obj, value),
+		.key_len = sizeof(int),
+		.hashfn = arch_fast_hash,
+		.mutex_is_held = &test_mutex_is_held,
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+	};
+	int err;
+
+	pr_info("Running resizable hashtable tests...\n");
+
+	err = rhashtable_init(&ht, &params);
+	if (err < 0) {
+		pr_warn("Test failed: Unable to initialize hashtable: %d\n",
+			err);
+		return err;
+	}
+
+	err = test_rhashtable(&ht);
+
+	rhashtable_destroy(&ht);
+
+	return err;
+}
+
+subsys_initcall(test_rht_init);
+
+#endif /* CONFIG_TEST_RHASHTABLE */
-- 
1.9.3

[PATCH net-next 1/3] lib: Resizable, Scalable, Concurrent Hash Table

[Thomas Graf]

Generic implementation of a resizable, scalable, concurrent hash table
based on [0]. The implementation supports both, fixed size keys specified
via an offset and length, or arbitrary keys via own hash and compare
functions.

Lookups are lockless and protected as RCU read side critical sections.
Automatic growing/shrinking based on user configurable watermarks is
available while allowing concurrent lookups to take place.

Objects to be hashed must include a struct rhash_head. The reason for not
using the existing struct hlist_head is that the expansion and shrinking
will have two buckets point to a single entry which would lead in obscure
reverse chaining behaviour.

Code includes a boot selftest if CONFIG_TEST_RHASHTABLE is defined.

[0] https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf

Signed-off-by: Thomas Graf <tgraf@suug.ch>
---
 include/linux/rhashtable.h | 213 ++++++++++++
 lib/Kconfig.debug          |   8 +
 lib/Makefile               |   2 +-
 lib/rhashtable.c           | 797 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 1019 insertions(+), 1 deletion(-)
 create mode 100644 include/linux/rhashtable.h
 create mode 100644 lib/rhashtable.c

diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
new file mode 100644
index 0000000..9cda293
--- /dev/null
+++ b/include/linux/rhashtable.h
@@ -0,0 +1,213 @@
+/*
+ * Resizable, Scalable, Concurrent Hash Table
+ *
+ * Copyright (c) 2014 Thomas Graf <tgraf@suug.ch>
+ * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
+ *
+ * Based on the following paper by Josh Triplett, Paul E. McKenney
+ * and Jonathan Walpole:
+ * https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf
+ *
+ * Code partially derived from nft_hash
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef _LINUX_RHASHTABLE_H
+#define _LINUX_RHASHTABLE_H
+
+#include <linux/rculist.h>
+
+struct rhash_head {
+	struct rhash_head		*next;
+};
+
+#define INIT_HASH_HEAD(ptr) ((ptr)->next = NULL)
+
+struct bucket_table {
+	size_t				size;
+	struct rhash_head __rcu		*buckets[];
+};
+
+typedef u32 (*rht_hashfn_t)(const void *data, u32 len, u32 seed);
+typedef u32 (*rht_obj_hashfn_t)(const void *data, u32 seed);
+
+struct rhashtable;
+
+/**
+ * struct rhashtable_params - Hash table construction parameters
+ * @nelem_hint: Hint on number of elements, should be 75% of desired size
+ * @key_len: Length of key
+ * @key_offset: Offset of key in struct to be hashed
+ * @head_offset: Offset of rhash_head in struct to be hashed
+ * @hash_rnd: Seed to use while hashing
+ * @max_shift: Maximum number of shifts while expanding
+ * @hashfn: Function to hash key
+ * @obj_hashfn: Function to hash object
+ * @grow_decision: If defined, may return true if table should expand
+ * @shrink_decision: If defined, may return true if table should shrink
+ * @mutex_is_held: Must return true if protecting mutex is held
+ */
+struct rhashtable_params {
+	size_t			nelem_hint;
+	size_t			key_len;
+	size_t			key_offset;
+	size_t			head_offset;
+	u32			hash_rnd;
+	size_t			max_shift;
+	rht_hashfn_t		hashfn;
+	rht_obj_hashfn_t	obj_hashfn;
+	bool			(*grow_decision)(const struct rhashtable *ht,
+						 size_t new_size);
+	bool			(*shrink_decision)(const struct rhashtable *ht,
+						   size_t new_size);
+	int			(*mutex_is_held)(void);
+};
+
+/**
+ * struct rhashtable - Hash table handle
+ * @tbl: Bucket table
+ * @nelems: Number of elements in table
+ * @shift: Current size (1 << shift)
+ * @p: Configuration parameters
+ */
+struct rhashtable {
+	struct bucket_table __rcu	*tbl;
+	size_t				nelems;
+	size_t				shift;
+	struct rhashtable_params	p;
+};
+
+#ifdef CONFIG_PROVE_LOCKING
+int lockdep_rht_mutex_is_held(const struct rhashtable *ht);
+#else
+static inline int lockdep_rht_mutex_is_held(const struct rhashtable *ht)
+{
+	return 1;
+}
+#endif /* CONFIG_PROVE_LOCKING */
+
+int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params);
+
+u32 rhashtable_hashfn(const struct rhashtable *ht, const void *key, u32 len);
+u32 rhashtable_obj_hashfn(const struct rhashtable *ht, void *ptr);
+
+void rhashtable_insert(struct rhashtable *ht, struct rhash_head *node, gfp_t);
+bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *node, gfp_t);
+void rhashtable_remove_pprev(struct rhashtable *ht, struct rhash_head *obj,
+			     struct rhash_head **pprev, gfp_t flags);
+
+bool rht_grow_above_75(const struct rhashtable *ht, size_t new_size);
+bool rht_shrink_below_30(const struct rhashtable *ht, size_t new_size);
+
+int rhashtable_expand(struct rhashtable *ht, gfp_t flags);
+int rhashtable_shrink(struct rhashtable *ht, gfp_t flags);
+
+void *rhashtable_lookup(const struct rhashtable *ht, const void *key);
+void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash,
+				bool (*compare)(void *, void *), void *arg);
+
+void rhashtable_destroy(const struct rhashtable *ht);
+
+#define rht_dereference(p, ht) \
+	rcu_dereference_protected(p, lockdep_rht_mutex_is_held(ht))
+
+#define rht_dereference_rcu(p, ht) \
+	rcu_dereference_check(p, lockdep_rht_mutex_is_held(ht))
+
+/* Internal, use rht_obj() instead */
+#define rht_entry(ptr, type, member) container_of(ptr, type, member)
+#define rht_entry_safe(ptr, type, member) \
+({ \
+	typeof(ptr) __ptr = (ptr); \
+	   __ptr ? rht_entry(__ptr, type, member) : NULL; \
+})
+#define rht_entry_safe_rcu(ptr, type, member) \
+({ \
+	typeof(*ptr) __rcu *__ptr = (typeof(*ptr) __rcu __force *)ptr; \
+	__ptr ? container_of((typeof(ptr))rcu_dereference_raw(__ptr), type, member) : NULL; \
+})
+
+#define rht_next_entry_safe(pos, ht, member) \
+({ \
+	pos ? rht_entry_safe(rht_dereference((pos)->member.next, ht), \
+			     typeof(*(pos)), member) : NULL; \
+})
+
+/**
+ * rht_for_each - iterate over hash chain
+ * @pos:	&struct rhash_head to use as a loop cursor.
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @ht:		pointer to your struct rhashtable
+ */
+#define rht_for_each(pos, head, ht) \
+	for (pos = rht_dereference(head, ht); \
+	     pos; \
+	     pos = rht_dereference((pos)->next, ht))
+
+/**
+ * rht_for_each_entry - iterate over hash chain of given type
+ * @pos:	type * to use as a loop cursor.
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @ht:		pointer to your struct rhashtable
+ * @member:	name of the rhash_head within the hashable struct.
+ */
+#define rht_for_each_entry(pos, head, ht, member) \
+	for (pos = rht_entry_safe(rht_dereference(head, ht), \
+				   typeof(*(pos)), member); \
+	     pos; \
+	     pos = rht_next_entry_safe(pos, ht, member))
+
+/**
+ * rht_for_each_entry_safe - safely iterate over hash chain of given type
+ * @pos:	type * to use as a loop cursor.
+ * @n:		type * to use for temporary next object storage
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @ht:		pointer to your struct rhashtable
+ * @member:	name of the rhash_head within the hashable struct.
+ *
+ * This hash chain list-traversal primitive allows for the looped code to
+ * remove the loop cursor from the list.
+ */
+#define rht_for_each_entry_safe(pos, n, head, ht, member)		\
+	for (pos = rht_entry_safe(rht_dereference(head, ht), \
+				  typeof(*(pos)), member), \
+	     n = rht_next_entry_safe(pos, ht, member); \
+	     pos; \
+	     pos = n, \
+	     n = rht_next_entry_safe(pos, ht, member))
+
+/**
+ * rht_for_each_rcu - iterate over rcu hash chain
+ * @pos:	&struct rhash_head to use as a loop cursor.
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @ht:		pointer to your struct rhashtable
+ *
+ * This hash chain list-traversal primitive may safely run concurrently with
+ * the _rcu fkht mutation primitives such as rht_insert() as long as the
+ * traversal is guarded by rcu_read_lock().
+ */
+#define rht_for_each_rcu(pos, head, ht) \
+	for (pos = rht_dereference_rcu(head, ht); \
+	     pos; \
+	     pos = rht_dereference_rcu((pos)->next, ht))
+
+/**
+ * rht_for_each_entry_rcu - iterate over rcu hash chain of given type
+ * @pos:	type * to use as a loop cursor.
+ * @head:	head of the hash chain (struct rhash_head *)
+ * @member:	name of the rhash_head within the hashable struct.
+ *
+ * This hash chain list-traversal primitive may safely run concurrently with
+ * the _rcu fkht mutation primitives such as rht_insert() as long as the
+ * traversal is guarded by rcu_read_lock().
+ */
+#define rht_for_each_entry_rcu(pos, head, member) \
+	for (pos = rht_entry_safe_rcu(head, typeof(*(pos)), member); \
+	     pos; \
+	     pos = rht_entry_safe_rcu((pos)->member.next, \
+				      typeof(*(pos)), member))
+
+#endif /* _LINUX_RHASHTABLE_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 7a638aa..f11a2e8 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1550,6 +1550,14 @@ config TEST_STRING_HELPERS
 config TEST_KSTRTOX
 	tristate "Test kstrto*() family of functions at runtime"
 
+config TEST_RHASHTABLE
+	bool "Perform selftest on resizable hash table"
+	default n
+	help
+	  Enable this option to test the rhashtable functions at boot.
+
+	  If unsure, say N.
+
 endmenu # runtime tests
 
 config PROVIDE_OHCI1394_DMA_INIT
diff --git a/lib/Makefile b/lib/Makefile
index ba967a1..fd248e4 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -26,7 +26,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
 	 bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
 	 gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \
 	 bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \
-	 percpu-refcount.o percpu_ida.o hash.o
+	 percpu-refcount.o percpu_ida.o hash.o rhashtable.o
 obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += kstrtox.o
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
new file mode 100644
index 0000000..e6940cf
--- /dev/null
+++ b/lib/rhashtable.c
@@ -0,0 +1,797 @@
+/*
+ * Resizable, Scalable, Concurrent Hash Table
+ *
+ * Copyright (c) 2014 Thomas Graf <tgraf@suug.ch>
+ * Copyright (c) 2008-2014 Patrick McHardy <kaber@trash.net>
+ *
+ * Based on the following paper:
+ * https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf
+ *
+ * Code partially derived from nft_hash
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/log2.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/mm.h>
+#include <linux/hash.h>
+#include <linux/random.h>
+#include <linux/rhashtable.h>
+#include <linux/log2.h>
+
+#define HASH_DEFAULT_SIZE	64UL
+#define HASH_MIN_SIZE		4UL
+
+#define ASSERT_RHT_MUTEX(HT) BUG_ON(!lockdep_rht_mutex_is_held(HT))
+
+#ifdef CONFIG_PROVE_LOCKING
+int lockdep_rht_mutex_is_held(const struct rhashtable *ht)
+{
+	return ht->p.mutex_is_held();
+}
+EXPORT_SYMBOL_GPL(lockdep_rht_mutex_is_held);
+#endif
+
+/**
+ * rht_obj - cast hash head to outer object
+ * @ht:		hash table
+ * @he:		hashed node
+ */
+void *rht_obj(const struct rhashtable *ht, const struct rhash_head *he)
+{
+	return (void *) he - ht->p.head_offset;
+}
+EXPORT_SYMBOL_GPL(rht_obj);
+
+static u32 __hashfn(const struct rhashtable *ht, const void *key,
+		      u32 len, u32 hsize)
+{
+	u32 h;
+
+	h = ht->p.hashfn(key, len, ht->p.hash_rnd);
+
+	return h & (hsize - 1);
+}
+
+/**
+ * rhashtable_hashfn - compute hash for key of given length
+ * @ht:		hash table to compuate for
+ * @key:	pointer to key
+ * @len:	length of key
+ *
+ * Computes the hash value using the hash function provided in the 'hashfn'
+ * of struct rhashtable_params. The returned value is guaranteed to be
+ * smaller than the number of buckets in the hash table.
+ */
+u32 rhashtable_hashfn(const struct rhashtable *ht, const void *key, u32 len)
+{
+	struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+
+	return __hashfn(ht, key, len, tbl->size);
+}
+EXPORT_SYMBOL_GPL(rhashtable_hashfn);
+
+static u32 obj_hashfn(const struct rhashtable *ht, const void *ptr, u32 hsize)
+{
+	if (unlikely(!ht->p.key_len)) {
+		u32 h;
+
+		h = ht->p.obj_hashfn(ptr, ht->p.hash_rnd);
+
+		return h & (hsize - 1);
+	}
+
+	return __hashfn(ht, ptr + ht->p.key_offset, ht->p.key_len, hsize);
+}
+
+/**
+ * rhashtable_obj_hashfn - compute hash for hashed object
+ * @ht:		hash table to compuate for
+ * @ptr:	pointer to hashed object
+ *
+ * Computes the hash value using the hash function `hashfn` respectively
+ * 'obj_hashfn' depending on whether the hash table is set up to work with
+ * a fixed length key. The returned value is guaranteed to be smaller than
+ * the number of buckets in the hash table.
+ */
+u32 rhashtable_obj_hashfn(const struct rhashtable *ht, void *ptr)
+{
+	struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+
+	return obj_hashfn(ht, ptr, tbl->size);
+}
+EXPORT_SYMBOL_GPL(rhashtable_obj_hashfn);
+
+static u32 head_hashfn(const struct rhashtable *ht,
+		       const struct rhash_head *he, u32 hsize)
+{
+	return obj_hashfn(ht, rht_obj(ht, he), hsize);
+}
+
+static struct bucket_table *bucket_table_alloc(size_t nbuckets, gfp_t flags)
+{
+	struct bucket_table *tbl;
+	size_t size;
+
+	size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
+	tbl = kzalloc(size, flags);
+	if (tbl == NULL)
+		tbl = vzalloc(size);
+
+	if (tbl == NULL)
+		return NULL;
+
+	tbl->size = nbuckets;
+
+	return tbl;
+}
+
+static void bucket_table_free(const struct bucket_table *tbl)
+{
+	kvfree(tbl);
+}
+
+/**
+ * rht_grow_above_75 - returns true if nelems > 0.75 * table-size
+ * @ht:		hash table
+ * @new_size:	new table size
+ */
+bool rht_grow_above_75(const struct rhashtable *ht, size_t new_size)
+{
+	/* Expand table when exceeding 75% load */
+	return ht->nelems > (new_size / 4 * 3);
+}
+EXPORT_SYMBOL_GPL(rht_grow_above_75);
+
+/**
+ * rht_shrink_below_30 - returns true if nelems < 0.3 * table-size
+ * @ht:		hash table
+ * @new_size:	new table size
+ */
+bool rht_shrink_below_30(const struct rhashtable *ht, size_t new_size)
+{
+	/* Shrink table beneath 30% load */
+	return ht->nelems < (new_size * 3 / 10);
+}
+EXPORT_SYMBOL_GPL(rht_shrink_below_30);
+
+static void hashtable_chain_unzip(const struct rhashtable *ht,
+				  const struct bucket_table *new_tbl,
+				  struct bucket_table *old_tbl, size_t n)
+{
+	struct rhash_head *he, *p, *next;
+	unsigned int h;
+
+	/* Old bucket empty, no work needed. */
+	p = rht_dereference(old_tbl->buckets[n], ht);
+	if (!p)
+		return;
+
+	/* Advance the old bucket pointer one or more times until it
+	 * reaches a node that doesn't hash to the same bucket as the
+	 * previous node p. Call the previous node p;
+	 */
+	h = head_hashfn(ht, p, new_tbl->size);
+	rht_for_each(he, p->next, ht) {
+		if (head_hashfn(ht, he, new_tbl->size) != h)
+			break;
+		p = he;
+	}
+	RCU_INIT_POINTER(old_tbl->buckets[n], p->next);
+
+	/* Find the subsequent node which does hash to the same
+	 * bucket as node P, or NULL if no such node exists.
+	 */
+	next = NULL;
+	if (he) {
+		rht_for_each(he, he->next, ht) {
+			if (head_hashfn(ht, he, new_tbl->size) == h) {
+				next = he;
+				break;
+			}
+		}
+	}
+
+	/* Set p's next pointer to that subsequent node pointer,
+	 * bypassing the nodes which do not hash to p's bucket
+	 */
+	RCU_INIT_POINTER(p->next, next);
+}
+
+/**
+ * rhashtable_expand - Expand hash table while allowing concurrent lookups
+ * @ht:		the hash table to expand
+ * @flags:	allocation flags
+ *
+ * A secondary bucket array is allocated and the hash entries are migrated
+ * while keeping them on both lists until the end of the RCU grace period.
+ *
+ * This function may only be called in a context where it is safe to call
+ * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
+ *
+ * The caller must ensure that no concurrent table mutations take place.
+ * It is however valid to have concurrent lookups if they are RCU protected.
+ */
+int rhashtable_expand(struct rhashtable *ht, gfp_t flags)
+{
+	struct bucket_table *new_tbl, *old_tbl = rht_dereference(ht->tbl, ht);
+	struct rhash_head *he;
+	unsigned int i, h;
+	bool complete;
+
+	ASSERT_RHT_MUTEX(ht);
+
+	if (ht->p.max_shift && ht->shift >= ht->p.max_shift)
+		return 0;
+
+	new_tbl = bucket_table_alloc(old_tbl->size * 2, flags);
+	if (new_tbl == NULL)
+		return -ENOMEM;
+
+	ht->shift++;
+
+	/* For each new bucket, search the corresponding old bucket
+	 * for the first entry that hashes to the new bucket, and
+	 * link the new bucket to that entry. Since all the entries
+	 * which will end up in the new bucket appear in the same
+	 * old bucket, this constructs an entirely valid new hash
+	 * table, but with multiple buckets "zipped" together into a
+	 * single imprecise chain.
+	 */
+	for (i = 0; i < new_tbl->size; i++) {
+		h = i & (old_tbl->size - 1);
+		rht_for_each(he, old_tbl->buckets[h], ht) {
+			if (head_hashfn(ht, he, new_tbl->size) == i) {
+				RCU_INIT_POINTER(new_tbl->buckets[i], he);
+				break;
+			}
+		}
+	}
+
+	/* Publish the new table pointer. Lookups may now traverse
+	 * the new table, but they will not benefit from any
+	 * additional efficiency until later steps unzip the buckets.
+	 */
+	rcu_assign_pointer(ht->tbl, new_tbl);
+
+	/* Unzip interleaved hash chains */
+	do {
+		/* Wait for readers. All new readers will see the new
+		 * table, and thus no references to the old table will
+		 * remain.
+		 */
+		synchronize_rcu();
+
+		/* For each bucket in the old table (each of which
+		 * contains items from multiple buckets of the new
+		 * table): ...
+		 */
+		complete = true;
+		for (i = 0; i < old_tbl->size; i++) {
+			hashtable_chain_unzip(ht, new_tbl, old_tbl, i);
+			if (old_tbl->buckets[i] != NULL)
+				complete = false;
+		}
+	} while (!complete);
+
+	bucket_table_free(old_tbl);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_expand);
+
+/**
+ * rhashtable_shrink - Shrink hash table while allowing concurrent lookups
+ * @ht:		the hash table to shrink
+ * @flags:	allocation flags
+ *
+ * This function may only be called in a context where it is safe to call
+ * synchronize_rcu(), e.g. not within a rcu_read_lock() section.
+ *
+ * The caller must ensure that no concurrent table mutations take place.
+ * It is however valid to have concurrent lookups if they are RCU protected.
+ */
+int rhashtable_shrink(struct rhashtable *ht, gfp_t flags)
+{
+	struct bucket_table *ntbl, *tbl = rht_dereference(ht->tbl, ht);
+	struct rhash_head __rcu **pprev;
+	unsigned int i;
+
+	ASSERT_RHT_MUTEX(ht);
+
+	if (tbl->size <= HASH_MIN_SIZE)
+		return 0;
+
+	ntbl = bucket_table_alloc(tbl->size / 2, flags);
+	if (ntbl == NULL)
+		return -ENOMEM;
+
+	ht->shift--;
+
+	/* Link each bucket in the new table to the first bucket
+	 * in the old table that contains entries which will hash
+	 * to the new bucket.
+	 */
+	for (i = 0; i < ntbl->size; i++) {
+		ntbl->buckets[i] = tbl->buckets[i];
+
+		/* Link each bucket in the new table to the first bucket
+		 * in the old table that contains entries which will hash
+		 * to the new bucket.
+		 */
+		for (pprev = &ntbl->buckets[i]; *pprev != NULL;
+		     pprev = &rht_dereference(*pprev, ht)->next)
+			;
+		RCU_INIT_POINTER(*pprev, tbl->buckets[i + ntbl->size]);
+	}
+
+	/* Publish the new, valid hash table */
+	rcu_assign_pointer(ht->tbl, ntbl);
+
+	/* Wait for readers. No new readers will have references to the
+	 * old hash table.
+	 */
+	synchronize_rcu();
+
+	bucket_table_free(tbl);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_shrink);
+
+/**
+ * rhashtable_insert - insert object into hash hash table
+ * @ht:		hash table
+ * @obj:	pointer to hash head inside object
+ * @flags:	allocation flags (table expansion)
+ *
+ * Will automatically grow the table via rhashtable_expand() if the the
+ * grow_decision function specified at rhashtable_init() returns true.
+ *
+ * The caller must ensure that no concurrent table mutations occur. It is
+ * however valid to have concurrent lookups if they are RCU protected.
+ */
+void rhashtable_insert(struct rhashtable *ht, struct rhash_head *obj,
+		       gfp_t flags)
+{
+	struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+	u32 hash;
+
+	ASSERT_RHT_MUTEX(ht);
+
+	hash = head_hashfn(ht, obj, tbl->size);
+	RCU_INIT_POINTER(obj->next, tbl->buckets[hash]);
+	rcu_assign_pointer(tbl->buckets[hash], obj);
+	ht->nelems++;
+
+	if (ht->p.grow_decision && ht->p.grow_decision(ht, tbl->size))
+		rhashtable_expand(ht, flags);
+}
+EXPORT_SYMBOL_GPL(rhashtable_insert);
+
+/**
+ * rhashtable_remove_pprev - remove object from hash table given previous element
+ * @ht:		hash table
+ * @obj:	pointer to hash head inside object
+ * @pprev:	pointer to previous element
+ * @flags:	allocation flags (table expansion)
+ *
+ * Identical to rhashtable_remove() but caller is alreayd aware of the element
+ * in front of the element to be deleted. This is in particular useful for
+ * deletion when combined with walking or lookup.
+ */
+void rhashtable_remove_pprev(struct rhashtable *ht, struct rhash_head *obj,
+			     struct rhash_head **pprev, gfp_t flags)
+{
+	struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+	ASSERT_RHT_MUTEX(ht);
+
+	RCU_INIT_POINTER(*pprev, obj->next);
+	ht->nelems--;
+
+	if (ht->p.shrink_decision &&
+	    ht->p.shrink_decision(ht, tbl->size))
+		rhashtable_shrink(ht, flags);
+}
+EXPORT_SYMBOL_GPL(rhashtable_remove_pprev);
+
+/**
+ * rhashtable_remove - remove object from hash table
+ * @ht:		hash table
+ * @obj:	pointer to hash head inside object
+ * @flags:	allocation flags (table expansion)
+ *
+ * Since the hash chain is single linked, the removal operation needs to
+ * walk the bucket chain upon removal. The removal operation is thus
+ * considerable slow if the hash table is not correctly sized.
+ *
+ * Will automatically shrink the table via rhashtable_expand() if the the
+ * shrink_decision function specified at rhashtable_init() returns true.
+ *
+ * The caller must ensure that no concurrent table mutations occur. It is
+ * however valid to have concurrent lookups if they are RCU protected.
+ */
+bool rhashtable_remove(struct rhashtable *ht, struct rhash_head *obj,
+		       gfp_t flags)
+{
+	struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+	struct rhash_head __rcu **pprev;
+	struct rhash_head *he;
+	u32 h;
+
+	ASSERT_RHT_MUTEX(ht);
+
+	h = head_hashfn(ht, obj, tbl->size);
+
+	pprev = &tbl->buckets[h];
+	rht_for_each(he, tbl->buckets[h], ht) {
+		if (he != obj) {
+			pprev = &he->next;
+			continue;
+		}
+
+		rhashtable_remove_pprev(ht, he, pprev, flags);
+		return true;
+	}
+
+	return false;
+}
+EXPORT_SYMBOL_GPL(rhashtable_remove);
+
+/**
+ * rhashtable_lookup - lookup key in hash table
+ * @ht:		hash table
+ * @key:	pointer to key
+ *
+ * Computes the hash value for the key and traverses the bucket chain looking
+ * for a entry with an identical key. The first matching entry is returned.
+ *
+ * This lookup function may only be used for fixed key hash table (key_len
+ * paramter set). It will BUG() if used inappropriately.
+ *
+ * Lookups may occur in parallel with hash mutations as long as the lookup is
+ * guarded by rcu_read_lock(). The caller must take care of this.
+ */
+void *rhashtable_lookup(const struct rhashtable *ht, const void *key)
+{
+	const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+	struct rhash_head *he;
+	u32 h;
+
+	BUG_ON(!ht->p.key_len);
+
+	h = __hashfn(ht, key, ht->p.key_len, tbl->size);
+	rht_for_each_rcu(he, tbl->buckets[h], ht) {
+		if (memcmp(rht_obj(ht, he) + ht->p.key_offset, key,
+			   ht->p.key_len))
+			continue;
+		return (void *) he - ht->p.head_offset;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(rhashtable_lookup);
+
+/**
+ * rhashtable_lookup_compare - search hash table with compare function
+ * @ht:		hash table
+ * @hash:	hash value of desired entry
+ * @compare:	compare function, must return true on match
+ * @arg:	argument passed on to compare function
+ *
+ * Traverses the bucket chain behind the provided hash value and calls the
+ * specified compare function for each entry.
+ *
+ * Lookups may occur in parallel with hash mutations as long as the lookup is
+ * guarded by rcu_read_lock(). The caller must take care of this.
+ *
+ * Returns the first entry on which the compare function returned true.
+ */
+void *rhashtable_lookup_compare(const struct rhashtable *ht, u32 hash,
+				bool (*compare)(void *, void *), void *arg)
+{
+	const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
+	struct rhash_head *he;
+
+	if (unlikely(hash >= tbl->size))
+		return NULL;
+
+	rht_for_each_rcu(he, tbl->buckets[hash], ht) {
+		if (!compare(rht_obj(ht, he), arg))
+			continue;
+		return (void *) he - ht->p.head_offset;
+	}
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(rhashtable_lookup_compare);
+
+static size_t rounded_hashtable_size(unsigned int nelem)
+{
+	return max(roundup_pow_of_two(nelem * 4 / 3), HASH_MIN_SIZE);
+}
+
+/**
+ * rhashtable_init - initialize a new hash table
+ * @ht:		hash table to be initialized
+ * @params:	configuration parameters
+ *
+ * Initializes a new hash table based on the provided configuration
+ * parameters. A table can be configured either with a variable or
+ * fixed length key:
+ *
+ * Configuration Example 1: Fixed length keys
+ * struct test_obj {
+ *	int			key;
+ *	void *			my_member;
+ *	struct rhash_head	node;
+ * };
+ *
+ * struct rhashtable_params params = {
+ *	.head_offset = offsetof(struct test_obj, node),
+ *	.key_offset = offsetof(struct test_obj, key),
+ *	.key_len = sizeof(int),
+ *	.hashfn = arch_fast_hash,
+ *	.mutex_is_held = &my_mutex_is_held,
+ * };
+ *
+ * Configuration Example 2: Variable length keys
+ * struct test_obj {
+ *	[...]
+ *	struct rhash_head	node;
+ * };
+ *
+ * u32 my_hash_fn(const void *data, u32 seed)
+ * {
+ *	struct test_obj *obj = data;
+ *
+ *	return [... hash ...];
+ * }
+ *
+ * struct rhashtable_params params = {
+ *	.head_offset = offsetof(struct test_obj, node),
+ *	.hashfn = arch_fast_hash,
+ *	.obj_hashfn = my_hash_fn,
+ *	.mutex_is_held = &my_mutex_is_held,
+ * };
+ */
+int rhashtable_init(struct rhashtable *ht, struct rhashtable_params *params)
+{
+	struct bucket_table *tbl;
+	size_t size;
+
+	size = HASH_DEFAULT_SIZE;
+
+	if ((params->key_len && !params->hashfn) ||
+	    (!params->key_len && !params->obj_hashfn))
+		return -EINVAL;
+
+	if (params->nelem_hint)
+		size = rounded_hashtable_size(params->nelem_hint);
+
+	tbl = bucket_table_alloc(size, GFP_KERNEL);
+	if (tbl == NULL)
+		return -ENOMEM;
+
+	memset(ht, 0, sizeof(*ht));
+	ht->shift = ilog2(tbl->size);
+	memcpy(&ht->p, params, sizeof(*params));
+	RCU_INIT_POINTER(ht->tbl, tbl);
+
+	if (!ht->p.hash_rnd)
+		get_random_bytes(&ht->p.hash_rnd, sizeof(ht->p.hash_rnd));
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(rhashtable_init);
+
+/**
+ * rhashtable_destroy - destroy hash table
+ * @ht:		the hash table to destroy
+ *
+ * Frees the bucket array.
+ */
+void rhashtable_destroy(const struct rhashtable *ht)
+{
+	const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+	bucket_table_free(tbl);
+}
+EXPORT_SYMBOL_GPL(rhashtable_destroy);
+
+/**************************************************************************
+ * Self Test
+ **************************************************************************/
+
+#ifdef CONFIG_TEST_RHASHTABLE
+
+#define TEST_HT_SIZE	8
+#define TEST_ENTRIES	2048
+#define TEST_PTR	((void *) 0xdeadbeef)
+#define TEST_NEXPANDS	4
+
+static int test_mutex_is_held(void)
+{
+	return 1;
+}
+
+struct test_obj {
+	void			*ptr;
+	int			value;
+	struct rhash_head	node;
+};
+
+static int __init test_rht_lookup(struct rhashtable *ht)
+{
+	unsigned int i;
+
+	for (i = 0; i < TEST_ENTRIES * 2; i++) {
+		struct test_obj *obj;
+		bool expected = !(i % 2);
+		u32 key = i;
+
+		obj = rhashtable_lookup(ht, &key);
+
+		if (expected && !obj) {
+			pr_warn("Test failed: Could not find key %u\n", key);
+			return -ENOENT;
+		} else if (!expected && obj) {
+			pr_warn("Test failed: Unexpected entry found for key %u\n",
+				key);
+			return -EEXIST;
+		} else if (expected && obj) {
+			if (obj->ptr != TEST_PTR || obj->value != i) {
+				pr_warn("Test failed: Lookup value mismatch %p!=%p, %u!=%u\n",
+					obj->ptr, TEST_PTR, obj->value, i);
+				return -EINVAL;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static void test_bucket_stats(struct rhashtable *ht,
+				     struct bucket_table *tbl,
+				     bool quiet)
+{
+	unsigned int cnt, i, total = 0;
+	struct test_obj *obj;
+
+	for (i = 0; i < tbl->size; i++) {
+		cnt = 0;
+
+		if (!quiet)
+			pr_info(" [%#4x/%zu]", i, tbl->size);
+
+		rht_for_each_entry_rcu(obj, tbl->buckets[i], node) {
+			cnt++;
+			total++;
+			if (!quiet)
+				pr_cont(" [%p],", obj);
+		}
+
+		if (!quiet)
+			pr_cont("\n  [%#x] first element: %p, chain length: %u\n",
+				i, tbl->buckets[i], cnt);
+	}
+
+	pr_info("  Traversal complete: counted=%u, nelems=%zu, entries=%d\n",
+		total, ht->nelems, TEST_ENTRIES);
+}
+
+static int __init test_rhashtable(struct rhashtable *ht)
+{
+	struct bucket_table *tbl;
+	struct test_obj *obj, *next;
+	int err;
+	unsigned int i;
+
+	/*
+	 * Insertion Test:
+	 * Insert TEST_ENTRIES into table with all keys even numbers
+	 */
+	pr_info("  Adding %d keys\n", TEST_ENTRIES);
+	for (i = 0; i < TEST_ENTRIES; i++) {
+		struct test_obj *obj;
+
+		obj = kzalloc(sizeof(*obj), GFP_KERNEL);
+		if (!obj) {
+			err = -ENOMEM;
+			goto error;
+		}
+
+		obj->ptr = TEST_PTR;
+		obj->value = i * 2;
+
+		rhashtable_insert(ht, &obj->node, GFP_KERNEL);
+	}
+
+	rcu_read_lock();
+	tbl = rht_dereference_rcu(ht->tbl, ht);
+	test_bucket_stats(ht, tbl, true);
+	test_rht_lookup(ht);
+	rcu_read_unlock();
+
+	for (i = 0; i < TEST_NEXPANDS; i++) {
+		pr_info("  Table expansion iteration %u...\n", i);
+		rhashtable_expand(ht, GFP_KERNEL);
+
+		rcu_read_lock();
+		pr_info("  Verifying lookups...\n");
+		test_rht_lookup(ht);
+		rcu_read_unlock();
+	}
+
+	for (i = 0; i < TEST_NEXPANDS; i++) {
+		pr_info("  Table shrinkage iteration %u...\n", i);
+		rhashtable_shrink(ht, GFP_KERNEL);
+
+		rcu_read_lock();
+		pr_info("  Verifying lookups...\n");
+		test_rht_lookup(ht);
+		rcu_read_unlock();
+	}
+
+	pr_info("  Deleting %d keys\n", TEST_ENTRIES);
+	for (i = 0; i < TEST_ENTRIES; i++) {
+		u32 key = i * 2;
+
+		obj = rhashtable_lookup(ht, &key);
+		BUG_ON(!obj);
+
+		rhashtable_remove(ht, &obj->node, GFP_KERNEL);
+		kfree(obj);
+	}
+
+	return 0;
+
+error:
+	tbl = rht_dereference_rcu(ht->tbl, ht);
+	for (i = 0; i < tbl->size; i++)
+		rht_for_each_entry_safe(obj, next, tbl->buckets[i], ht, node)
+			kfree(obj);
+
+	return err;
+}
+
+static int __init test_rht_init(void)
+{
+	struct rhashtable ht;
+	struct rhashtable_params params = {
+		.nelem_hint = TEST_HT_SIZE,
+		.head_offset = offsetof(struct test_obj, node),
+		.key_offset = offsetof(struct test_obj, value),
+		.key_len = sizeof(int),
+		.hashfn = arch_fast_hash,
+		.mutex_is_held = &test_mutex_is_held,
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+	};
+	int err;
+
+	pr_info("Running resizable hashtable tests...\n");
+
+	err = rhashtable_init(&ht, &params);
+	if (err < 0) {
+		pr_warn("Test failed: Unable to initialize hashtable: %d\n",
+			err);
+		return err;
+	}
+
+	err = test_rhashtable(&ht);
+
+	rhashtable_destroy(&ht);
+
+	return err;
+}
+
+subsys_initcall(test_rht_init);
+
+#endif /* CONFIG_TEST_RHASHTABLE */
-- 
1.9.3

_______________________________________________
dev mailing list
dev@openvswitch.org
http://openvswitch.org/mailman/listinfo/dev

[PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

Heavy Netlink users such as Open vSwitch spend a considerable amount of
time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
RCU relieves the lock contention.

Makes use of the new resizable hash table to avoid locking on the
lookup.

The hash table will grow if entries exceeds 75% of table size up to a
total table size of 64K. It will automatically shrink if usage falls
below 50%.

Also splits nl_table_lock into a separate spinlock to protect hash table
mutations. This avoids a possible deadlock when the hash table growing
waits on RCU readers to complete via synchronize_rcu() while readers
holding RCU read lock are waiting on the nl_table_lock() to be released
to lock the table for broadcasting.

Before:
   9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
   4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
   3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2

After:
  15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
   3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
   [...]
   0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup

Signed-off-by: Thomas Graf <tgraf@suug.ch>
---
 net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
 net/netlink/af_netlink.h |  18 +--
 net/netlink/diag.c       |  11 +-
 3 files changed, 119 insertions(+), 195 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index ce82722..05b7e5e 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -58,7 +58,9 @@
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>
 #include <linux/if_arp.h>
+#include <linux/rhashtable.h>
 #include <asm/cacheflush.h>
+#include <linux/hash.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -100,6 +102,18 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 #define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
 
+/* Protects netlink socket hash table mutations */
+DEFINE_MUTEX(nl_sk_hash_lock);
+
+static int lockdep_nl_sk_hash_is_held(void)
+{
+#ifdef CONFIG_LOCKDEP
+	return (debug_locks) ? lockdep_is_held(&nl_sk_hash_lock) : 1;
+#else
+	return 1;
+#endif
+}
+
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static DEFINE_SPINLOCK(netlink_tap_lock);
@@ -110,11 +124,6 @@ static inline u32 netlink_group_mask(u32 group)
 	return group ? 1 << (group - 1) : 0;
 }
 
-static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u32 portid)
-{
-	return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
-}
-
 int netlink_add_tap(struct netlink_tap *nt)
 {
 	if (unlikely(nt->dev->type != ARPHRD_NETLINK))
@@ -983,105 +992,48 @@ netlink_unlock_table(void)
 		wake_up(&nl_table_wait);
 }
 
-static bool netlink_compare(struct net *net, struct sock *sk)
-{
-	return net_eq(sock_net(sk), net);
-}
-
-static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
+struct netlink_compare_arg
 {
-	struct netlink_table *table = &nl_table[protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *sk;
-
-	read_lock(&nl_table_lock);
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(sk, head) {
-		if (table->compare(net, sk) &&
-		    (nlk_sk(sk)->portid == portid)) {
-			sock_hold(sk);
-			goto found;
-		}
-	}
-	sk = NULL;
-found:
-	read_unlock(&nl_table_lock);
-	return sk;
-}
+	struct net *net;
+	u32 portid;
+};
 
-static struct hlist_head *nl_portid_hash_zalloc(size_t size)
+static bool netlink_compare(void *ptr, void *arg)
 {
-	if (size <= PAGE_SIZE)
-		return kzalloc(size, GFP_ATOMIC);
-	else
-		return (struct hlist_head *)
-			__get_free_pages(GFP_ATOMIC | __GFP_ZERO,
-					 get_order(size));
-}
+	struct netlink_compare_arg *x = arg;
+	struct sock *sk = ptr;
 
-static void nl_portid_hash_free(struct hlist_head *table, size_t size)
-{
-	if (size <= PAGE_SIZE)
-		kfree(table);
-	else
-		free_pages((unsigned long)table, get_order(size));
+	return nlk_sk(sk)->portid == x->portid &&
+	       net_eq(sock_net(sk), x->net);
 }
 
-static int nl_portid_hash_rehash(struct nl_portid_hash *hash, int grow)
+static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
+				     struct net *net)
 {
-	unsigned int omask, mask, shift;
-	size_t osize, size;
-	struct hlist_head *otable, *table;
-	int i;
-
-	omask = mask = hash->mask;
-	osize = size = (mask + 1) * sizeof(*table);
-	shift = hash->shift;
-
-	if (grow) {
-		if (++shift > hash->max_shift)
-			return 0;
-		mask = mask * 2 + 1;
-		size *= 2;
-	}
+	struct netlink_compare_arg arg = {
+		.net = net,
+		.portid = portid,
+	};
+	u32 hash;
 
-	table = nl_portid_hash_zalloc(size);
-	if (!table)
-		return 0;
+	hash = rhashtable_hashfn(&table->hash, &portid, sizeof(portid));
 
-	otable = hash->table;
-	hash->table = table;
-	hash->mask = mask;
-	hash->shift = shift;
-	get_random_bytes(&hash->rnd, sizeof(hash->rnd));
-
-	for (i = 0; i <= omask; i++) {
-		struct sock *sk;
-		struct hlist_node *tmp;
-
-		sk_for_each_safe(sk, tmp, &otable[i])
-			__sk_add_node(sk, nl_portid_hashfn(hash, nlk_sk(sk)->portid));
-	}
-
-	nl_portid_hash_free(otable, osize);
-	hash->rehash_time = jiffies + 10 * 60 * HZ;
-	return 1;
+	return rhashtable_lookup_compare(&table->hash, hash,
+					 &netlink_compare, &arg);
 }
 
-static inline int nl_portid_hash_dilute(struct nl_portid_hash *hash, int len)
+static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
 {
-	int avg = hash->entries >> hash->shift;
-
-	if (unlikely(avg > 1) && nl_portid_hash_rehash(hash, 1))
-		return 1;
+	struct netlink_table *table = &nl_table[protocol];
+	struct sock *sk;
 
-	if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
-		nl_portid_hash_rehash(hash, 0);
-		return 1;
-	}
+	rcu_read_lock();
+	sk = __netlink_lookup(table, portid, net);
+	if (sk)
+		sock_hold(sk);
+	rcu_read_unlock();
 
-	return 0;
+	return sk;
 }
 
 static const struct proto_ops netlink_ops;
@@ -1113,22 +1065,10 @@ netlink_update_listeners(struct sock *sk)
 static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 {
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
 	int err = -EADDRINUSE;
-	struct sock *osk;
-	int len;
 
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	len = 0;
-	sk_for_each(osk, head) {
-		if (table->compare(net, osk) &&
-		    (nlk_sk(osk)->portid == portid))
-			break;
-		len++;
-	}
-	if (osk)
+	mutex_lock(&nl_sk_hash_lock);
+	if (__netlink_lookup(table, portid, net))
 		goto err;
 
 	err = -EBUSY;
@@ -1136,26 +1076,31 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 		goto err;
 
 	err = -ENOMEM;
-	if (BITS_PER_LONG > 32 && unlikely(hash->entries >= UINT_MAX))
+	if (BITS_PER_LONG > 32 && unlikely(table->hash.nelems >= UINT_MAX))
 		goto err;
 
-	if (len && nl_portid_hash_dilute(hash, len))
-		head = nl_portid_hashfn(hash, portid);
-	hash->entries++;
 	nlk_sk(sk)->portid = portid;
-	sk_add_node(sk, head);
+	sock_hold(sk);
+	rhashtable_insert(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC);
 	err = 0;
-
 err:
-	netlink_table_ungrab();
+	mutex_unlock(&nl_sk_hash_lock);
 	return err;
 }
 
 static void netlink_remove(struct sock *sk)
 {
+	struct netlink_table *table;
+
+	mutex_lock(&nl_sk_hash_lock);
+	table = &nl_table[sk->sk_protocol];
+	if (rhashtable_remove(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC)) {
+		WARN_ON(atomic_read(&sk->sk_refcnt) == 1);
+		__sock_put(sk);
+	}
+	mutex_unlock(&nl_sk_hash_lock);
+
 	netlink_table_grab();
-	if (sk_del_node_init(sk))
-		nl_table[sk->sk_protocol].hash.entries--;
 	if (nlk_sk(sk)->subscriptions)
 		__sk_del_bind_node(sk);
 	netlink_table_ungrab();
@@ -1311,6 +1256,9 @@ static int netlink_release(struct socket *sock)
 	}
 	netlink_table_ungrab();
 
+	/* Wait for readers to complete */
+	synchronize_net();
+
 	kfree(nlk->groups);
 	nlk->groups = NULL;
 
@@ -1326,30 +1274,22 @@ static int netlink_autobind(struct socket *sock)
 	struct sock *sk = sock->sk;
 	struct net *net = sock_net(sk);
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *osk;
 	s32 portid = task_tgid_vnr(current);
 	int err;
 	static s32 rover = -4097;
 
 retry:
 	cond_resched();
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(osk, head) {
-		if (!table->compare(net, osk))
-			continue;
-		if (nlk_sk(osk)->portid == portid) {
-			/* Bind collision, search negative portid values. */
-			portid = rover--;
-			if (rover > -4097)
-				rover = -4097;
-			netlink_table_ungrab();
-			goto retry;
-		}
+	rcu_read_lock();
+	if (__netlink_lookup(table, portid, net)) {
+		/* Bind collision, search negative portid values. */
+		portid = rover--;
+		if (rover > -4097)
+			rover = -4097;
+		rcu_read_unlock();
+		goto retry;
 	}
-	netlink_table_ungrab();
+	rcu_read_unlock();
 
 	err = netlink_insert(sk, net, portid);
 	if (err == -EADDRINUSE)
@@ -2953,14 +2893,18 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 {
 	struct nl_seq_iter *iter = seq->private;
 	int i, j;
+	struct netlink_sock *nlk;
 	struct sock *s;
 	loff_t off = 0;
 
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+		for (j = 0; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				s = (struct sock *)nlk;
 
-		for (j = 0; j <= hash->mask; j++) {
-			sk_for_each(s, &hash->table[j]) {
 				if (sock_net(s) != seq_file_net(seq))
 					continue;
 				if (off == pos) {
@@ -2976,15 +2920,14 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 }
 
 static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(nl_table_lock)
 {
-	read_lock(&nl_table_lock);
+	rcu_read_lock();
 	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
 }
 
 static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct sock *s;
+	struct netlink_sock *nlk;
 	struct nl_seq_iter *iter;
 	struct net *net;
 	int i, j;
@@ -2996,28 +2939,26 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	net = seq_file_net(seq);
 	iter = seq->private;
-	s = v;
-	do {
-		s = sk_next(s);
-	} while (s && !nl_table[s->sk_protocol].compare(net, s));
-	if (s)
-		return s;
+	nlk = v;
+
+	rht_for_each_entry_rcu(nlk, nlk->node.next, node)
+		if (net_eq(sock_net((struct sock *)nlk), net))
+			return nlk;
 
 	i = iter->link;
 	j = iter->hash_idx + 1;
 
 	do {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		for (; j <= hash->mask; j++) {
-			s = sk_head(&hash->table[j]);
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
 
-			while (s && !nl_table[s->sk_protocol].compare(net, s))
-				s = sk_next(s);
-			if (s) {
-				iter->link = i;
-				iter->hash_idx = j;
-				return s;
+		for (; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				if (net_eq(sock_net((struct sock *)nlk), net)) {
+					iter->link = i;
+					iter->hash_idx = j;
+					return nlk;
+				}
 			}
 		}
 
@@ -3028,9 +2969,8 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void netlink_seq_stop(struct seq_file *seq, void *v)
-	__releases(nl_table_lock)
 {
-	read_unlock(&nl_table_lock);
+	rcu_read_unlock();
 }
 
 
@@ -3168,9 +3108,17 @@ static struct pernet_operations __net_initdata netlink_net_ops = {
 static int __init netlink_proto_init(void)
 {
 	int i;
-	unsigned long limit;
-	unsigned int order;
 	int err = proto_register(&netlink_proto, 0);
+	struct rhashtable_params ht_params = {
+		.head_offset = offsetof(struct netlink_sock, node),
+		.key_offset = offsetof(struct netlink_sock, portid),
+		.key_len = sizeof(u32), /* portid */
+		.hashfn = arch_fast_hash,
+		.max_shift = 16, /* 64K */
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+		.mutex_is_held = lockdep_nl_sk_hash_is_held,
+	};
 
 	if (err != 0)
 		goto out;
@@ -3181,32 +3129,13 @@ static int __init netlink_proto_init(void)
 	if (!nl_table)
 		goto panic;
 
-	if (totalram_pages >= (128 * 1024))
-		limit = totalram_pages >> (21 - PAGE_SHIFT);
-	else
-		limit = totalram_pages >> (23 - PAGE_SHIFT);
-
-	order = get_bitmask_order(limit) - 1 + PAGE_SHIFT;
-	limit = (1UL << order) / sizeof(struct hlist_head);
-	order = get_bitmask_order(min(limit, (unsigned long)UINT_MAX)) - 1;
-
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		hash->table = nl_portid_hash_zalloc(1 * sizeof(*hash->table));
-		if (!hash->table) {
-			while (i-- > 0)
-				nl_portid_hash_free(nl_table[i].hash.table,
-						 1 * sizeof(*hash->table));
+		if (rhashtable_init(&nl_table[i].hash, &ht_params) < 0) {
+			while (--i > 0)
+				rhashtable_destroy(&nl_table[i].hash);
 			kfree(nl_table);
 			goto panic;
 		}
-		hash->max_shift = order;
-		hash->shift = 0;
-		hash->mask = 0;
-		hash->rehash_time = jiffies;
-
-		nl_table[i].compare = netlink_compare;
 	}
 
 	INIT_LIST_HEAD(&netlink_tap_all);
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d44..60f631f 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -1,6 +1,7 @@
 #ifndef _AF_NETLINK_H
 #define _AF_NETLINK_H
 
+#include <linux/rhashtable.h>
 #include <net/sock.h>
 
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -47,6 +48,8 @@ struct netlink_sock {
 	struct netlink_ring	tx_ring;
 	atomic_t		mapped;
 #endif /* CONFIG_NETLINK_MMAP */
+
+	struct rhash_head	node;
 };
 
 static inline struct netlink_sock *nlk_sk(struct sock *sk)
@@ -54,21 +57,8 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
 	return container_of(sk, struct netlink_sock, sk);
 }
 
-struct nl_portid_hash {
-	struct hlist_head	*table;
-	unsigned long		rehash_time;
-
-	unsigned int		mask;
-	unsigned int		shift;
-
-	unsigned int		entries;
-	unsigned int		max_shift;
-
-	u32			rnd;
-};
-
 struct netlink_table {
-	struct nl_portid_hash	hash;
+	struct rhashtable	hash;
 	struct hlist_head	mc_list;
 	struct listeners __rcu	*listeners;
 	unsigned int		flags;
diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index 1af29624..7301850 100644
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -4,6 +4,7 @@
 #include <linux/netlink.h>
 #include <linux/sock_diag.h>
 #include <linux/netlink_diag.h>
+#include <linux/rhashtable.h>
 
 #include "af_netlink.h"
 
@@ -101,16 +102,20 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 				int protocol, int s_num)
 {
 	struct netlink_table *tbl = &nl_table[protocol];
-	struct nl_portid_hash *hash = &tbl->hash;
+	struct rhashtable *ht = &tbl->hash;
+	const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
 	struct net *net = sock_net(skb->sk);
 	struct netlink_diag_req *req;
+	struct netlink_sock *nlsk;
 	struct sock *sk;
 	int ret = 0, num = 0, i;
 
 	req = nlmsg_data(cb->nlh);
 
-	for (i = 0; i <= hash->mask; i++) {
-		sk_for_each(sk, &hash->table[i]) {
+	for (i = 0; i < htbl->size; i++) {
+		rht_for_each_entry(nlsk, htbl->buckets[i], ht, node) {
+			sk = (struct sock *)nlsk;
+
 			if (!net_eq(sock_net(sk), net))
 				continue;
 			if (num < s_num) {
-- 
1.9.3

[PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

Heavy Netlink users such as Open vSwitch spend a considerable amount of
time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
RCU relieves the lock contention.

Makes use of the new resizable hash table to avoid locking on the
lookup.

The hash table will grow if entries exceeds 75% of table size up to a
total table size of 64K. It will automatically shrink if usage falls
below 50%.

Also splits nl_table_lock into a separate spinlock to protect hash table
mutations. This avoids a possible deadlock when the hash table growing
waits on RCU readers to complete via synchronize_rcu() while readers
holding RCU read lock are waiting on the nl_table_lock() to be released
to lock the table for broadcasting.

Before:
   9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
   4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
   3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2

After:
  15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
   3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
   [...]
   0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup

Signed-off-by: Thomas Graf <tgraf-G/eBtMaohhA@public.gmane.org>
---
 net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
 net/netlink/af_netlink.h |  18 +--
 net/netlink/diag.c       |  11 +-
 3 files changed, 119 insertions(+), 195 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index ce82722..05b7e5e 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -58,7 +58,9 @@
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>
 #include <linux/if_arp.h>
+#include <linux/rhashtable.h>
 #include <asm/cacheflush.h>
+#include <linux/hash.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -100,6 +102,18 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 #define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
 
+/* Protects netlink socket hash table mutations */
+DEFINE_MUTEX(nl_sk_hash_lock);
+
+static int lockdep_nl_sk_hash_is_held(void)
+{
+#ifdef CONFIG_LOCKDEP
+	return (debug_locks) ? lockdep_is_held(&nl_sk_hash_lock) : 1;
+#else
+	return 1;
+#endif
+}
+
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static DEFINE_SPINLOCK(netlink_tap_lock);
@@ -110,11 +124,6 @@ static inline u32 netlink_group_mask(u32 group)
 	return group ? 1 << (group - 1) : 0;
 }
 
-static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u32 portid)
-{
-	return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
-}
-
 int netlink_add_tap(struct netlink_tap *nt)
 {
 	if (unlikely(nt->dev->type != ARPHRD_NETLINK))
@@ -983,105 +992,48 @@ netlink_unlock_table(void)
 		wake_up(&nl_table_wait);
 }
 
-static bool netlink_compare(struct net *net, struct sock *sk)
-{
-	return net_eq(sock_net(sk), net);
-}
-
-static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
+struct netlink_compare_arg
 {
-	struct netlink_table *table = &nl_table[protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *sk;
-
-	read_lock(&nl_table_lock);
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(sk, head) {
-		if (table->compare(net, sk) &&
-		    (nlk_sk(sk)->portid == portid)) {
-			sock_hold(sk);
-			goto found;
-		}
-	}
-	sk = NULL;
-found:
-	read_unlock(&nl_table_lock);
-	return sk;
-}
+	struct net *net;
+	u32 portid;
+};
 
-static struct hlist_head *nl_portid_hash_zalloc(size_t size)
+static bool netlink_compare(void *ptr, void *arg)
 {
-	if (size <= PAGE_SIZE)
-		return kzalloc(size, GFP_ATOMIC);
-	else
-		return (struct hlist_head *)
-			__get_free_pages(GFP_ATOMIC | __GFP_ZERO,
-					 get_order(size));
-}
+	struct netlink_compare_arg *x = arg;
+	struct sock *sk = ptr;
 
-static void nl_portid_hash_free(struct hlist_head *table, size_t size)
-{
-	if (size <= PAGE_SIZE)
-		kfree(table);
-	else
-		free_pages((unsigned long)table, get_order(size));
+	return nlk_sk(sk)->portid == x->portid &&
+	       net_eq(sock_net(sk), x->net);
 }
 
-static int nl_portid_hash_rehash(struct nl_portid_hash *hash, int grow)
+static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
+				     struct net *net)
 {
-	unsigned int omask, mask, shift;
-	size_t osize, size;
-	struct hlist_head *otable, *table;
-	int i;
-
-	omask = mask = hash->mask;
-	osize = size = (mask + 1) * sizeof(*table);
-	shift = hash->shift;
-
-	if (grow) {
-		if (++shift > hash->max_shift)
-			return 0;
-		mask = mask * 2 + 1;
-		size *= 2;
-	}
+	struct netlink_compare_arg arg = {
+		.net = net,
+		.portid = portid,
+	};
+	u32 hash;
 
-	table = nl_portid_hash_zalloc(size);
-	if (!table)
-		return 0;
+	hash = rhashtable_hashfn(&table->hash, &portid, sizeof(portid));
 
-	otable = hash->table;
-	hash->table = table;
-	hash->mask = mask;
-	hash->shift = shift;
-	get_random_bytes(&hash->rnd, sizeof(hash->rnd));
-
-	for (i = 0; i <= omask; i++) {
-		struct sock *sk;
-		struct hlist_node *tmp;
-
-		sk_for_each_safe(sk, tmp, &otable[i])
-			__sk_add_node(sk, nl_portid_hashfn(hash, nlk_sk(sk)->portid));
-	}
-
-	nl_portid_hash_free(otable, osize);
-	hash->rehash_time = jiffies + 10 * 60 * HZ;
-	return 1;
+	return rhashtable_lookup_compare(&table->hash, hash,
+					 &netlink_compare, &arg);
 }
 
-static inline int nl_portid_hash_dilute(struct nl_portid_hash *hash, int len)
+static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
 {
-	int avg = hash->entries >> hash->shift;
-
-	if (unlikely(avg > 1) && nl_portid_hash_rehash(hash, 1))
-		return 1;
+	struct netlink_table *table = &nl_table[protocol];
+	struct sock *sk;
 
-	if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
-		nl_portid_hash_rehash(hash, 0);
-		return 1;
-	}
+	rcu_read_lock();
+	sk = __netlink_lookup(table, portid, net);
+	if (sk)
+		sock_hold(sk);
+	rcu_read_unlock();
 
-	return 0;
+	return sk;
 }
 
 static const struct proto_ops netlink_ops;
@@ -1113,22 +1065,10 @@ netlink_update_listeners(struct sock *sk)
 static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 {
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
 	int err = -EADDRINUSE;
-	struct sock *osk;
-	int len;
 
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	len = 0;
-	sk_for_each(osk, head) {
-		if (table->compare(net, osk) &&
-		    (nlk_sk(osk)->portid == portid))
-			break;
-		len++;
-	}
-	if (osk)
+	mutex_lock(&nl_sk_hash_lock);
+	if (__netlink_lookup(table, portid, net))
 		goto err;
 
 	err = -EBUSY;
@@ -1136,26 +1076,31 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 		goto err;
 
 	err = -ENOMEM;
-	if (BITS_PER_LONG > 32 && unlikely(hash->entries >= UINT_MAX))
+	if (BITS_PER_LONG > 32 && unlikely(table->hash.nelems >= UINT_MAX))
 		goto err;
 
-	if (len && nl_portid_hash_dilute(hash, len))
-		head = nl_portid_hashfn(hash, portid);
-	hash->entries++;
 	nlk_sk(sk)->portid = portid;
-	sk_add_node(sk, head);
+	sock_hold(sk);
+	rhashtable_insert(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC);
 	err = 0;
-
 err:
-	netlink_table_ungrab();
+	mutex_unlock(&nl_sk_hash_lock);
 	return err;
 }
 
 static void netlink_remove(struct sock *sk)
 {
+	struct netlink_table *table;
+
+	mutex_lock(&nl_sk_hash_lock);
+	table = &nl_table[sk->sk_protocol];
+	if (rhashtable_remove(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC)) {
+		WARN_ON(atomic_read(&sk->sk_refcnt) == 1);
+		__sock_put(sk);
+	}
+	mutex_unlock(&nl_sk_hash_lock);
+
 	netlink_table_grab();
-	if (sk_del_node_init(sk))
-		nl_table[sk->sk_protocol].hash.entries--;
 	if (nlk_sk(sk)->subscriptions)
 		__sk_del_bind_node(sk);
 	netlink_table_ungrab();
@@ -1311,6 +1256,9 @@ static int netlink_release(struct socket *sock)
 	}
 	netlink_table_ungrab();
 
+	/* Wait for readers to complete */
+	synchronize_net();
+
 	kfree(nlk->groups);
 	nlk->groups = NULL;
 
@@ -1326,30 +1274,22 @@ static int netlink_autobind(struct socket *sock)
 	struct sock *sk = sock->sk;
 	struct net *net = sock_net(sk);
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *osk;
 	s32 portid = task_tgid_vnr(current);
 	int err;
 	static s32 rover = -4097;
 
 retry:
 	cond_resched();
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(osk, head) {
-		if (!table->compare(net, osk))
-			continue;
-		if (nlk_sk(osk)->portid == portid) {
-			/* Bind collision, search negative portid values. */
-			portid = rover--;
-			if (rover > -4097)
-				rover = -4097;
-			netlink_table_ungrab();
-			goto retry;
-		}
+	rcu_read_lock();
+	if (__netlink_lookup(table, portid, net)) {
+		/* Bind collision, search negative portid values. */
+		portid = rover--;
+		if (rover > -4097)
+			rover = -4097;
+		rcu_read_unlock();
+		goto retry;
 	}
-	netlink_table_ungrab();
+	rcu_read_unlock();
 
 	err = netlink_insert(sk, net, portid);
 	if (err == -EADDRINUSE)
@@ -2953,14 +2893,18 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 {
 	struct nl_seq_iter *iter = seq->private;
 	int i, j;
+	struct netlink_sock *nlk;
 	struct sock *s;
 	loff_t off = 0;
 
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+		for (j = 0; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				s = (struct sock *)nlk;
 
-		for (j = 0; j <= hash->mask; j++) {
-			sk_for_each(s, &hash->table[j]) {
 				if (sock_net(s) != seq_file_net(seq))
 					continue;
 				if (off == pos) {
@@ -2976,15 +2920,14 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 }
 
 static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(nl_table_lock)
 {
-	read_lock(&nl_table_lock);
+	rcu_read_lock();
 	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
 }
 
 static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct sock *s;
+	struct netlink_sock *nlk;
 	struct nl_seq_iter *iter;
 	struct net *net;
 	int i, j;
@@ -2996,28 +2939,26 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	net = seq_file_net(seq);
 	iter = seq->private;
-	s = v;
-	do {
-		s = sk_next(s);
-	} while (s && !nl_table[s->sk_protocol].compare(net, s));
-	if (s)
-		return s;
+	nlk = v;
+
+	rht_for_each_entry_rcu(nlk, nlk->node.next, node)
+		if (net_eq(sock_net((struct sock *)nlk), net))
+			return nlk;
 
 	i = iter->link;
 	j = iter->hash_idx + 1;
 
 	do {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		for (; j <= hash->mask; j++) {
-			s = sk_head(&hash->table[j]);
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
 
-			while (s && !nl_table[s->sk_protocol].compare(net, s))
-				s = sk_next(s);
-			if (s) {
-				iter->link = i;
-				iter->hash_idx = j;
-				return s;
+		for (; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				if (net_eq(sock_net((struct sock *)nlk), net)) {
+					iter->link = i;
+					iter->hash_idx = j;
+					return nlk;
+				}
 			}
 		}
 
@@ -3028,9 +2969,8 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void netlink_seq_stop(struct seq_file *seq, void *v)
-	__releases(nl_table_lock)
 {
-	read_unlock(&nl_table_lock);
+	rcu_read_unlock();
 }
 
 
@@ -3168,9 +3108,17 @@ static struct pernet_operations __net_initdata netlink_net_ops = {
 static int __init netlink_proto_init(void)
 {
 	int i;
-	unsigned long limit;
-	unsigned int order;
 	int err = proto_register(&netlink_proto, 0);
+	struct rhashtable_params ht_params = {
+		.head_offset = offsetof(struct netlink_sock, node),
+		.key_offset = offsetof(struct netlink_sock, portid),
+		.key_len = sizeof(u32), /* portid */
+		.hashfn = arch_fast_hash,
+		.max_shift = 16, /* 64K */
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+		.mutex_is_held = lockdep_nl_sk_hash_is_held,
+	};
 
 	if (err != 0)
 		goto out;
@@ -3181,32 +3129,13 @@ static int __init netlink_proto_init(void)
 	if (!nl_table)
 		goto panic;
 
-	if (totalram_pages >= (128 * 1024))
-		limit = totalram_pages >> (21 - PAGE_SHIFT);
-	else
-		limit = totalram_pages >> (23 - PAGE_SHIFT);
-
-	order = get_bitmask_order(limit) - 1 + PAGE_SHIFT;
-	limit = (1UL << order) / sizeof(struct hlist_head);
-	order = get_bitmask_order(min(limit, (unsigned long)UINT_MAX)) - 1;
-
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		hash->table = nl_portid_hash_zalloc(1 * sizeof(*hash->table));
-		if (!hash->table) {
-			while (i-- > 0)
-				nl_portid_hash_free(nl_table[i].hash.table,
-						 1 * sizeof(*hash->table));
+		if (rhashtable_init(&nl_table[i].hash, &ht_params) < 0) {
+			while (--i > 0)
+				rhashtable_destroy(&nl_table[i].hash);
 			kfree(nl_table);
 			goto panic;
 		}
-		hash->max_shift = order;
-		hash->shift = 0;
-		hash->mask = 0;
-		hash->rehash_time = jiffies;
-
-		nl_table[i].compare = netlink_compare;
 	}
 
 	INIT_LIST_HEAD(&netlink_tap_all);
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d44..60f631f 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -1,6 +1,7 @@
 #ifndef _AF_NETLINK_H
 #define _AF_NETLINK_H
 
+#include <linux/rhashtable.h>
 #include <net/sock.h>
 
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -47,6 +48,8 @@ struct netlink_sock {
 	struct netlink_ring	tx_ring;
 	atomic_t		mapped;
 #endif /* CONFIG_NETLINK_MMAP */
+
+	struct rhash_head	node;
 };
 
 static inline struct netlink_sock *nlk_sk(struct sock *sk)
@@ -54,21 +57,8 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
 	return container_of(sk, struct netlink_sock, sk);
 }
 
-struct nl_portid_hash {
-	struct hlist_head	*table;
-	unsigned long		rehash_time;
-
-	unsigned int		mask;
-	unsigned int		shift;
-
-	unsigned int		entries;
-	unsigned int		max_shift;
-
-	u32			rnd;
-};
-
 struct netlink_table {
-	struct nl_portid_hash	hash;
+	struct rhashtable	hash;
 	struct hlist_head	mc_list;
 	struct listeners __rcu	*listeners;
 	unsigned int		flags;
diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index 1af29624..7301850 100644
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -4,6 +4,7 @@
 #include <linux/netlink.h>
 #include <linux/sock_diag.h>
 #include <linux/netlink_diag.h>
+#include <linux/rhashtable.h>
 
 #include "af_netlink.h"
 
@@ -101,16 +102,20 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 				int protocol, int s_num)
 {
 	struct netlink_table *tbl = &nl_table[protocol];
-	struct nl_portid_hash *hash = &tbl->hash;
+	struct rhashtable *ht = &tbl->hash;
+	const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
 	struct net *net = sock_net(skb->sk);
 	struct netlink_diag_req *req;
+	struct netlink_sock *nlsk;
 	struct sock *sk;
 	int ret = 0, num = 0, i;
 
 	req = nlmsg_data(cb->nlh);
 
-	for (i = 0; i <= hash->mask; i++) {
-		sk_for_each(sk, &hash->table[i]) {
+	for (i = 0; i < htbl->size; i++) {
+		rht_for_each_entry(nlsk, htbl->buckets[i], ht, node) {
+			sk = (struct sock *)nlsk;
+
 			if (!net_eq(sock_net(sk), net))
 				continue;
 			if (num < s_num) {
-- 
1.9.3

[PATCH net-next 3/3] nftables: Convert nft_hash to use generic rhashtable

[Thomas Graf]

The sizing of the hash table and the practice of requiring a lookup
to retrieve the pprev to be stored in the element cookie before the
deletion of an entry is left intact.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Patrick McHardy <kaber@trash.net>
---
 net/netfilter/nft_hash.c | 292 +++++++++--------------------------------------
 1 file changed, 54 insertions(+), 238 deletions(-)

diff --git a/net/netfilter/nft_hash.c b/net/netfilter/nft_hash.c
index 4080ed6..35059d2 100644
--- a/net/netfilter/nft_hash.c
+++ b/net/netfilter/nft_hash.c
@@ -15,209 +15,40 @@
 #include <linux/log2.h>
 #include <linux/jhash.h>
 #include <linux/netlink.h>
-#include <linux/vmalloc.h>
+#include <linux/rhashtable.h>
 #include <linux/netfilter.h>
 #include <linux/netfilter/nf_tables.h>
 #include <net/netfilter/nf_tables.h>
 
-#define NFT_HASH_MIN_SIZE	4UL
-
-struct nft_hash {
-	struct nft_hash_table __rcu	*tbl;
-};
-
-struct nft_hash_table {
-	unsigned int			size;
-	struct nft_hash_elem __rcu	*buckets[];
-};
+/* We target a hash table size of 4, element hint is 75% of final size */
+#define NFT_HASH_ELEMENT_HINT 3
 
 struct nft_hash_elem {
-	struct nft_hash_elem __rcu	*next;
+	struct rhash_head		node;
 	struct nft_data			key;
 	struct nft_data			data[];
 };
 
-#define nft_hash_for_each_entry(i, head) \
-	for (i = nft_dereference(head); i != NULL; i = nft_dereference(i->next))
-#define nft_hash_for_each_entry_rcu(i, head) \
-	for (i = rcu_dereference(head); i != NULL; i = rcu_dereference(i->next))
-
-static u32 nft_hash_rnd __read_mostly;
-static bool nft_hash_rnd_initted __read_mostly;
-
-static unsigned int nft_hash_data(const struct nft_data *data,
-				  unsigned int hsize, unsigned int len)
-{
-	unsigned int h;
-
-	h = jhash(data->data, len, nft_hash_rnd);
-	return h & (hsize - 1);
-}
-
 static bool nft_hash_lookup(const struct nft_set *set,
 			    const struct nft_data *key,
 			    struct nft_data *data)
 {
-	const struct nft_hash *priv = nft_set_priv(set);
-	const struct nft_hash_table *tbl = rcu_dereference(priv->tbl);
+	const struct rhashtable *priv = nft_set_priv(set);
 	const struct nft_hash_elem *he;
-	unsigned int h;
-
-	h = nft_hash_data(key, tbl->size, set->klen);
-	nft_hash_for_each_entry_rcu(he, tbl->buckets[h]) {
-		if (nft_data_cmp(&he->key, key, set->klen))
-			continue;
-		if (set->flags & NFT_SET_MAP)
-			nft_data_copy(data, he->data);
-		return true;
-	}
-	return false;
-}
-
-static void nft_hash_tbl_free(const struct nft_hash_table *tbl)
-{
-	kvfree(tbl);
-}
-
-static unsigned int nft_hash_tbl_size(unsigned int nelem)
-{
-	return max(roundup_pow_of_two(nelem * 4 / 3), NFT_HASH_MIN_SIZE);
-}
-
-static struct nft_hash_table *nft_hash_tbl_alloc(unsigned int nbuckets)
-{
-	struct nft_hash_table *tbl;
-	size_t size;
-
-	size = sizeof(*tbl) + nbuckets * sizeof(tbl->buckets[0]);
-	tbl = kzalloc(size, GFP_KERNEL | __GFP_REPEAT | __GFP_NOWARN);
-	if (tbl == NULL)
-		tbl = vzalloc(size);
-	if (tbl == NULL)
-		return NULL;
-	tbl->size = nbuckets;
-
-	return tbl;
-}
-
-static void nft_hash_chain_unzip(const struct nft_set *set,
-				 const struct nft_hash_table *ntbl,
-				 struct nft_hash_table *tbl, unsigned int n)
-{
-	struct nft_hash_elem *he, *last, *next;
-	unsigned int h;
-
-	he = nft_dereference(tbl->buckets[n]);
-	if (he == NULL)
-		return;
-	h = nft_hash_data(&he->key, ntbl->size, set->klen);
-
-	/* Find last element of first chain hashing to bucket h */
-	last = he;
-	nft_hash_for_each_entry(he, he->next) {
-		if (nft_hash_data(&he->key, ntbl->size, set->klen) != h)
-			break;
-		last = he;
-	}
-
-	/* Unlink first chain from the old table */
-	RCU_INIT_POINTER(tbl->buckets[n], last->next);
-
-	/* If end of chain reached, done */
-	if (he == NULL)
-		return;
-
-	/* Find first element of second chain hashing to bucket h */
-	next = NULL;
-	nft_hash_for_each_entry(he, he->next) {
-		if (nft_hash_data(&he->key, ntbl->size, set->klen) != h)
-			continue;
-		next = he;
-		break;
-	}
-
-	/* Link the two chains */
-	RCU_INIT_POINTER(last->next, next);
-}
-
-static int nft_hash_tbl_expand(const struct nft_set *set, struct nft_hash *priv)
-{
-	struct nft_hash_table *tbl = nft_dereference(priv->tbl), *ntbl;
-	struct nft_hash_elem *he;
-	unsigned int i, h;
-	bool complete;
-
-	ntbl = nft_hash_tbl_alloc(tbl->size * 2);
-	if (ntbl == NULL)
-		return -ENOMEM;
-
-	/* Link new table's buckets to first element in the old table
-	 * hashing to the new bucket.
-	 */
-	for (i = 0; i < ntbl->size; i++) {
-		h = i < tbl->size ? i : i - tbl->size;
-		nft_hash_for_each_entry(he, tbl->buckets[h]) {
-			if (nft_hash_data(&he->key, ntbl->size, set->klen) != i)
-				continue;
-			RCU_INIT_POINTER(ntbl->buckets[i], he);
-			break;
-		}
-	}
-
-	/* Publish new table */
-	rcu_assign_pointer(priv->tbl, ntbl);
 
-	/* Unzip interleaved hash chains */
-	do {
-		/* Wait for readers to use new table/unzipped chains */
-		synchronize_rcu();
+	he = rhashtable_lookup(priv, key);
+	if (he && set->flags & NFT_SET_MAP)
+		nft_data_copy(data, he->data);
 
-		complete = true;
-		for (i = 0; i < tbl->size; i++) {
-			nft_hash_chain_unzip(set, ntbl, tbl, i);
-			if (tbl->buckets[i] != NULL)
-				complete = false;
-		}
-	} while (!complete);
-
-	nft_hash_tbl_free(tbl);
-	return 0;
-}
-
-static int nft_hash_tbl_shrink(const struct nft_set *set, struct nft_hash *priv)
-{
-	struct nft_hash_table *tbl = nft_dereference(priv->tbl), *ntbl;
-	struct nft_hash_elem __rcu **pprev;
-	unsigned int i;
-
-	ntbl = nft_hash_tbl_alloc(tbl->size / 2);
-	if (ntbl == NULL)
-		return -ENOMEM;
-
-	for (i = 0; i < ntbl->size; i++) {
-		ntbl->buckets[i] = tbl->buckets[i];
-
-		for (pprev = &ntbl->buckets[i]; *pprev != NULL;
-		     pprev = &nft_dereference(*pprev)->next)
-			;
-		RCU_INIT_POINTER(*pprev, tbl->buckets[i + ntbl->size]);
-	}
-
-	/* Publish new table */
-	rcu_assign_pointer(priv->tbl, ntbl);
-	synchronize_rcu();
-
-	nft_hash_tbl_free(tbl);
-	return 0;
+	return !!he;
 }
 
 static int nft_hash_insert(const struct nft_set *set,
 			   const struct nft_set_elem *elem)
 {
-	struct nft_hash *priv = nft_set_priv(set);
-	struct nft_hash_table *tbl = nft_dereference(priv->tbl);
+	struct rhashtable *priv = nft_set_priv(set);
 	struct nft_hash_elem *he;
-	unsigned int size, h;
+	unsigned int size;
 
 	if (elem->flags != 0)
 		return -EINVAL;
@@ -234,13 +65,7 @@ static int nft_hash_insert(const struct nft_set *set,
 	if (set->flags & NFT_SET_MAP)
 		nft_data_copy(he->data, &elem->data);
 
-	h = nft_hash_data(&he->key, tbl->size, set->klen);
-	RCU_INIT_POINTER(he->next, tbl->buckets[h]);
-	rcu_assign_pointer(tbl->buckets[h], he);
-
-	/* Expand table when exceeding 75% load */
-	if (set->nelems + 1 > tbl->size / 4 * 3)
-		nft_hash_tbl_expand(set, priv);
+	rhashtable_insert(priv, &he->node, GFP_KERNEL);
 
 	return 0;
 }
@@ -257,36 +82,28 @@ static void nft_hash_elem_destroy(const struct nft_set *set,
 static void nft_hash_remove(const struct nft_set *set,
 			    const struct nft_set_elem *elem)
 {
-	struct nft_hash *priv = nft_set_priv(set);
-	struct nft_hash_table *tbl = nft_dereference(priv->tbl);
-	struct nft_hash_elem *he, __rcu **pprev;
+	struct rhashtable *priv = nft_set_priv(set);
+	struct rhash_head *he, __rcu **pprev;
 
 	pprev = elem->cookie;
-	he = nft_dereference((*pprev));
-
-	RCU_INIT_POINTER(*pprev, he->next);
-	synchronize_rcu();
-	kfree(he);
+	he = rht_dereference((*pprev), priv);
 
-	/* Shrink table beneath 30% load */
-	if (set->nelems - 1 < tbl->size * 3 / 10 &&
-	    tbl->size > NFT_HASH_MIN_SIZE)
-		nft_hash_tbl_shrink(set, priv);
+	rhashtable_remove_pprev(priv, he, pprev, GFP_KERNEL);
 }
 
 static int nft_hash_get(const struct nft_set *set, struct nft_set_elem *elem)
 {
-	const struct nft_hash *priv = nft_set_priv(set);
-	const struct nft_hash_table *tbl = nft_dereference(priv->tbl);
-	struct nft_hash_elem __rcu * const *pprev;
+	const struct rhashtable *priv = nft_set_priv(set);
+	const struct bucket_table *tbl = rht_dereference_rcu(priv->tbl, priv);
+	struct rhash_head __rcu * const *pprev;
 	struct nft_hash_elem *he;
-	unsigned int h;
+	u32 h;
 
-	h = nft_hash_data(&elem->key, tbl->size, set->klen);
+	h = rhashtable_hashfn(priv, &elem->key, set->klen);
 	pprev = &tbl->buckets[h];
-	nft_hash_for_each_entry(he, tbl->buckets[h]) {
+	rht_for_each_entry_rcu(he, tbl->buckets[h], node) {
 		if (nft_data_cmp(&he->key, &elem->key, set->klen)) {
-			pprev = &he->next;
+			pprev = &he->node.next;
 			continue;
 		}
 
@@ -302,14 +119,15 @@ static int nft_hash_get(const struct nft_set *set, struct nft_set_elem *elem)
 static void nft_hash_walk(const struct nft_ctx *ctx, const struct nft_set *set,
 			  struct nft_set_iter *iter)
 {
-	const struct nft_hash *priv = nft_set_priv(set);
-	const struct nft_hash_table *tbl = nft_dereference(priv->tbl);
+	const struct rhashtable *priv = nft_set_priv(set);
+	const struct bucket_table *tbl;
 	const struct nft_hash_elem *he;
 	struct nft_set_elem elem;
 	unsigned int i;
 
+	tbl = rht_dereference_rcu(priv->tbl, priv);
 	for (i = 0; i < tbl->size; i++) {
-		nft_hash_for_each_entry(he, tbl->buckets[i]) {
+		rht_for_each_entry_rcu(he, tbl->buckets[i], node) {
 			if (iter->count < iter->skip)
 				goto cont;
 
@@ -329,48 +147,46 @@ cont:
 
 static unsigned int nft_hash_privsize(const struct nlattr * const nla[])
 {
-	return sizeof(struct nft_hash);
+	return sizeof(struct rhashtable);
+}
+
+static int lockdep_nfnl_lock_is_held(void)
+{
+	return lockdep_nfnl_is_held(NFNL_SUBSYS_NFTABLES);
 }
 
 static int nft_hash_init(const struct nft_set *set,
 			 const struct nft_set_desc *desc,
 			 const struct nlattr * const tb[])
 {
-	struct nft_hash *priv = nft_set_priv(set);
-	struct nft_hash_table *tbl;
-	unsigned int size;
+	struct rhashtable *priv = nft_set_priv(set);
+	struct rhashtable_params params = {
+		.nelem_hint = desc->size ? : NFT_HASH_ELEMENT_HINT,
+		.head_offset = offsetof(struct nft_hash_elem, node),
+		.key_offset = offsetof(struct nft_hash_elem, key),
+		.key_len = set->klen,
+		.hashfn = jhash,
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+		.mutex_is_held = lockdep_nfnl_lock_is_held,
+	};
 
-	if (unlikely(!nft_hash_rnd_initted)) {
-		get_random_bytes(&nft_hash_rnd, 4);
-		nft_hash_rnd_initted = true;
-	}
-
-	size = NFT_HASH_MIN_SIZE;
-	if (desc->size)
-		size = nft_hash_tbl_size(desc->size);
-
-	tbl = nft_hash_tbl_alloc(size);
-	if (tbl == NULL)
-		return -ENOMEM;
-	RCU_INIT_POINTER(priv->tbl, tbl);
-	return 0;
+	return rhashtable_init(priv, &params);
 }
 
 static void nft_hash_destroy(const struct nft_set *set)
 {
-	const struct nft_hash *priv = nft_set_priv(set);
-	const struct nft_hash_table *tbl = nft_dereference(priv->tbl);
+	const struct rhashtable *priv = nft_set_priv(set);
+	const struct bucket_table *tbl;
 	struct nft_hash_elem *he, *next;
 	unsigned int i;
 
-	for (i = 0; i < tbl->size; i++) {
-		for (he = nft_dereference(tbl->buckets[i]); he != NULL;
-		     he = next) {
-			next = nft_dereference(he->next);
+	tbl = rht_dereference(priv->tbl, priv);
+	for (i = 0; i < tbl->size; i++)
+		rht_for_each_entry_safe(he, next, tbl->buckets[i], priv, node)
 			nft_hash_elem_destroy(set, he);
-		}
-	}
-	kfree(tbl);
+
+	rhashtable_destroy(priv);
 }
 
 static bool nft_hash_estimate(const struct nft_set_desc *desc, u32 features,
@@ -383,8 +199,8 @@ static bool nft_hash_estimate(const struct nft_set_desc *desc, u32 features,
 		esize += FIELD_SIZEOF(struct nft_hash_elem, data[0]);
 
 	if (desc->size) {
-		est->size = sizeof(struct nft_hash) +
-			    nft_hash_tbl_size(desc->size) *
+		est->size = sizeof(struct rhashtable) +
+			    roundup_pow_of_two(desc->size * 4 / 3) *
 			    sizeof(struct nft_hash_elem *) +
 			    desc->size * esize;
 	} else {
-- 
1.9.3

Re: [PATCH net-next 3/3] nftables: Convert nft_hash to use generic rhashtable

[Nikolay Aleksandrov]

On 08/01/2014 01:58 PM, Thomas Graf wrote:
> The sizing of the hash table and the practice of requiring a lookup
> to retrieve the pprev to be stored in the element cookie before the
> deletion of an entry is left intact.
> 
> Signed-off-by: Thomas Graf <tgraf@suug.ch>
> Acked-by: Patrick McHardy <kaber@trash.net>
> ---
<<snip>>
> @@ -257,36 +82,28 @@ static void nft_hash_elem_destroy(const struct nft_set *set,
>  static void nft_hash_remove(const struct nft_set *set,
>  			    const struct nft_set_elem *elem)
>  {
> -	struct nft_hash *priv = nft_set_priv(set);
> -	struct nft_hash_table *tbl = nft_dereference(priv->tbl);
> -	struct nft_hash_elem *he, __rcu **pprev;
> +	struct rhashtable *priv = nft_set_priv(set);
> +	struct rhash_head *he, __rcu **pprev;
>  
>  	pprev = elem->cookie;
> -	he = nft_dereference((*pprev));
> -
> -	RCU_INIT_POINTER(*pprev, he->next);
> -	synchronize_rcu();
> -	kfree(he);
> +	he = rht_dereference((*pprev), priv);
>  
> -	/* Shrink table beneath 30% load */
> -	if (set->nelems - 1 < tbl->size * 3 / 10 &&
> -	    tbl->size > NFT_HASH_MIN_SIZE)
> -		nft_hash_tbl_shrink(set, priv);
> +	rhashtable_remove_pprev(priv, he, pprev, GFP_KERNEL);
>  }
<<snip>>
Hi again,
Sorry for the late response but I just got around to check the 3rd patch now,
so my question about this fragment is: before nft_hash_remove() would free the
element after removal, but after this change I don't see where and when the
removed element would get freed ?

Nik

Re: [PATCH net-next 3/3] nftables: Convert nft_hash to use generic rhashtable

[Nikolay Aleksandrov]

On 08/01/2014 01:58 PM, Thomas Graf wrote:
> The sizing of the hash table and the practice of requiring a lookup
> to retrieve the pprev to be stored in the element cookie before the
> deletion of an entry is left intact.
> 
> Signed-off-by: Thomas Graf <tgraf-G/eBtMaohhA@public.gmane.org>
> Acked-by: Patrick McHardy <kaber-dcUjhNyLwpNeoWH0uzbU5w@public.gmane.org>
> ---
<<snip>>
> @@ -257,36 +82,28 @@ static void nft_hash_elem_destroy(const struct nft_set *set,
>  static void nft_hash_remove(const struct nft_set *set,
>  			    const struct nft_set_elem *elem)
>  {
> -	struct nft_hash *priv = nft_set_priv(set);
> -	struct nft_hash_table *tbl = nft_dereference(priv->tbl);
> -	struct nft_hash_elem *he, __rcu **pprev;
> +	struct rhashtable *priv = nft_set_priv(set);
> +	struct rhash_head *he, __rcu **pprev;
>  
>  	pprev = elem->cookie;
> -	he = nft_dereference((*pprev));
> -
> -	RCU_INIT_POINTER(*pprev, he->next);
> -	synchronize_rcu();
> -	kfree(he);
> +	he = rht_dereference((*pprev), priv);
>  
> -	/* Shrink table beneath 30% load */
> -	if (set->nelems - 1 < tbl->size * 3 / 10 &&
> -	    tbl->size > NFT_HASH_MIN_SIZE)
> -		nft_hash_tbl_shrink(set, priv);
> +	rhashtable_remove_pprev(priv, he, pprev, GFP_KERNEL);
>  }
<<snip>>
Hi again,
Sorry for the late response but I just got around to check the 3rd patch now,
so my question about this fragment is: before nft_hash_remove() would free the
element after removal, but after this change I don't see where and when the
removed element would get freed ?

Nik

Re: [PATCH net-next 3/3] nftables: Convert nft_hash to use generic rhashtable

[Thomas Graf]

On 08/01/14 at 02:21pm, Nikolay Aleksandrov wrote:
> Sorry for the late response but I just got around to check the 3rd patch now,
> so my question about this fragment is: before nft_hash_remove() would free the
> element after removal, but after this change I don't see where and when the
> removed element would get freed ?

You are right. Looking at this closer we were leaking references even
before the change because it would not call nft_data_uninit() to release
the data objects. So it should really just call nft_hash_elem_destroy().

Re: [PATCH net-next 3/3] nftables: Convert nft_hash to use generic rhashtable

[Patrick McHardy]

On 1. August 2014 14:49:01 GMT+01:00, Thomas Graf <tgraf@suug.ch> wrote:
>On 08/01/14 at 02:21pm, Nikolay Aleksandrov wrote:
>> Sorry for the late response but I just got around to check the 3rd
>patch now,
>> so my question about this fragment is: before nft_hash_remove() would
>free the
>> element after removal, but after this change I don't see where and
>when the
>> removed element would get freed ?
>
>You are right. Looking at this closer we were leaking references even
>before the change because it would not call nft_data_uninit() to
>release
>the data objects. So it should really just call
>nft_hash_elem_destroy().

No, the data uninit is performed by the set core. Just freeing it is fine.

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Nikolay Aleksandrov]

On 08/01/2014 01:58 PM, Thomas Graf wrote:
> Heavy Netlink users such as Open vSwitch spend a considerable amount of
> time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
> RCU relieves the lock contention.
> 
> Makes use of the new resizable hash table to avoid locking on the
> lookup.
> 
> The hash table will grow if entries exceeds 75% of table size up to a
> total table size of 64K. It will automatically shrink if usage falls
> below 50%.
> 
> Also splits nl_table_lock into a separate spinlock to protect hash table
> mutations. This avoids a possible deadlock when the hash table growing
> waits on RCU readers to complete via synchronize_rcu() while readers
> holding RCU read lock are waiting on the nl_table_lock() to be released
> to lock the table for broadcasting.
> 
> Before:
>    9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
>    6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
>    6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
>    6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
>    4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
>    4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
>    3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
>    2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
> 
> After:
>   15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
>    8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
>    7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
>    5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
>    4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
>    4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
>    3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
>    [...]
>    0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
> 
> Signed-off-by: Thomas Graf <tgraf@suug.ch>
> ---

Hmm, in both the rhashtable_insert() and rhashtable_remove() calls in the
netlink code you're using GFP_ATOMIC flags but if rhashtable_expand/shring gets
called even though the allocation will be with GFP_ATOMIC, they still call
synchronize_rcu() which may block. Now I'm not familiar with the netlink code,
but I think that in general the flags are useless for GFP_ATOMIC because of the
calls to synchronize_rcu() in expand/shrink which can block anyway.
Just a thought, I may be missing something of course.

Nik

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Nikolay Aleksandrov]

On 08/01/2014 01:58 PM, Thomas Graf wrote:
> Heavy Netlink users such as Open vSwitch spend a considerable amount of
> time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
> RCU relieves the lock contention.
> 
> Makes use of the new resizable hash table to avoid locking on the
> lookup.
> 
> The hash table will grow if entries exceeds 75% of table size up to a
> total table size of 64K. It will automatically shrink if usage falls
> below 50%.
> 
> Also splits nl_table_lock into a separate spinlock to protect hash table
> mutations. This avoids a possible deadlock when the hash table growing
> waits on RCU readers to complete via synchronize_rcu() while readers
> holding RCU read lock are waiting on the nl_table_lock() to be released
> to lock the table for broadcasting.
> 
> Before:
>    9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
>    6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
>    6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
>    6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
>    4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
>    4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
>    3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
>    2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
> 
> After:
>   15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
>    8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
>    7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
>    5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
>    4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
>    4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
>    3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
>    [...]
>    0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
> 
> Signed-off-by: Thomas Graf <tgraf-G/eBtMaohhA@public.gmane.org>
> ---

Hmm, in both the rhashtable_insert() and rhashtable_remove() calls in the
netlink code you're using GFP_ATOMIC flags but if rhashtable_expand/shring gets
called even though the allocation will be with GFP_ATOMIC, they still call
synchronize_rcu() which may block. Now I'm not familiar with the netlink code,
but I think that in general the flags are useless for GFP_ATOMIC because of the
calls to synchronize_rcu() in expand/shrink which can block anyway.
Just a thought, I may be missing something of course.

Nik

Re: [PATCH net-next 3/3] nftables: Convert nft_hash to use generic rhashtable

[Thomas Graf]

On 08/01/14 at 03:12pm, Patrick McHardy wrote:
> On 1. August 2014 14:49:01 GMT+01:00, Thomas Graf <tgraf@suug.ch> wrote:
> >On 08/01/14 at 02:21pm, Nikolay Aleksandrov wrote:
> >> Sorry for the late response but I just got around to check the 3rd
> >patch now,
> >> so my question about this fragment is: before nft_hash_remove() would
> >free the
> >> element after removal, but after this change I don't see where and
> >when the
> >> removed element would get freed ?
> >
> >You are right. Looking at this closer we were leaking references even
> >before the change because it would not call nft_data_uninit() to
> >release
> >the data objects. So it should really just call
> >nft_hash_elem_destroy().
> 
> No, the data uninit is performed by the set core. Just freeing it is fine.

OK, I can see the uninit on the data in nft_del_setelem() for maps
prior to the actual commit. The location is slightly unexpected since
the element is still findable in the hash table at that point.

I'll wait a short while to see if there is more feedback and resubmit
afterwards.

Re: [PATCH net-next 3/3] nftables: Convert nft_hash to use generic rhashtable

[Patrick McHardy]

On 1. August 2014 15:51:45 GMT+01:00, Thomas Graf <tgraf@suug.ch> wrote:
>On 08/01/14 at 03:12pm, Patrick McHardy wrote:
>> On 1. August 2014 14:49:01 GMT+01:00, Thomas Graf <tgraf@suug.ch>
>wrote:
>> >On 08/01/14 at 02:21pm, Nikolay Aleksandrov wrote:
>> >> Sorry for the late response but I just got around to check the 3rd
>> >patch now,
>> >> so my question about this fragment is: before nft_hash_remove()
>would
>> >free the
>> >> element after removal, but after this change I don't see where and
>> >when the
>> >> removed element would get freed ?
>> >
>> >You are right. Looking at this closer we were leaking references
>even
>> >before the change because it would not call nft_data_uninit() to
>> >release
>> >the data objects. So it should really just call
>> >nft_hash_elem_destroy().
>> 
>> No, the data uninit is performed by the set core. Just freeing it is
>fine.
>
>OK, I can see the uninit on the data in nft_del_setelem() for maps
>prior to the actual commit. The location is slightly unexpected since
>the element is still findable in the hash table at that point.

That's most likely a bug from the transaction API.

Pablo?

>I'll wait a short while to see if there is more feedback and resubmit
>afterwards.

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

On 08/01/14 at 04:51pm, Nikolay Aleksandrov wrote:
> Hmm, in both the rhashtable_insert() and rhashtable_remove() calls in the
> netlink code you're using GFP_ATOMIC flags but if rhashtable_expand/shring gets
> called even though the allocation will be with GFP_ATOMIC, they still call
> synchronize_rcu() which may block. Now I'm not familiar with the netlink code,
> but I think that in general the flags are useless for GFP_ATOMIC because of the
> calls to synchronize_rcu() in expand/shrink which can block anyway.
> Just a thought, I may be missing something of course.

I don't think you are missing anything. The GFP_ATOMIC flag was
inherited from how the bucket table was allocated prior to the
convertion to the new hash table but you are right, it can't be
needed since the table protection was converted to a mutex.
Using GFP_KERNEL will have a better chance of succeeding.

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

On 08/01/14 at 04:51pm, Nikolay Aleksandrov wrote:
> Hmm, in both the rhashtable_insert() and rhashtable_remove() calls in the
> netlink code you're using GFP_ATOMIC flags but if rhashtable_expand/shring gets
> called even though the allocation will be with GFP_ATOMIC, they still call
> synchronize_rcu() which may block. Now I'm not familiar with the netlink code,
> but I think that in general the flags are useless for GFP_ATOMIC because of the
> calls to synchronize_rcu() in expand/shrink which can block anyway.
> Just a thought, I may be missing something of course.

I don't think you are missing anything. The GFP_ATOMIC flag was
inherited from how the bucket table was allocated prior to the
convertion to the new hash table but you are right, it can't be
needed since the table protection was converted to a mutex.
Using GFP_KERNEL will have a better chance of succeeding.

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Nikolay Aleksandrov]

On 08/01/2014 05:15 PM, Thomas Graf wrote:
> On 08/01/14 at 04:51pm, Nikolay Aleksandrov wrote:
>> Hmm, in both the rhashtable_insert() and rhashtable_remove() calls in the
>> netlink code you're using GFP_ATOMIC flags but if rhashtable_expand/shring gets
>> called even though the allocation will be with GFP_ATOMIC, they still call
>> synchronize_rcu() which may block. Now I'm not familiar with the netlink code,
>> but I think that in general the flags are useless for GFP_ATOMIC because of the
>> calls to synchronize_rcu() in expand/shrink which can block anyway.
>> Just a thought, I may be missing something of course.
> 
> I don't think you are missing anything. The GFP_ATOMIC flag was
> inherited from how the bucket table was allocated prior to the
> convertion to the new hash table but you are right, it can't be
> needed since the table protection was converted to a mutex.
> Using GFP_KERNEL will have a better chance of succeeding.
> 
Right, I was wondering why it was atomic in the first place and couldn't find a
good reason from the code :-)
But that explains it.

Cheers,
 Nik

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Nikolay Aleksandrov]

On 08/01/2014 05:15 PM, Thomas Graf wrote:
> On 08/01/14 at 04:51pm, Nikolay Aleksandrov wrote:
>> Hmm, in both the rhashtable_insert() and rhashtable_remove() calls in the
>> netlink code you're using GFP_ATOMIC flags but if rhashtable_expand/shring gets
>> called even though the allocation will be with GFP_ATOMIC, they still call
>> synchronize_rcu() which may block. Now I'm not familiar with the netlink code,
>> but I think that in general the flags are useless for GFP_ATOMIC because of the
>> calls to synchronize_rcu() in expand/shrink which can block anyway.
>> Just a thought, I may be missing something of course.
> 
> I don't think you are missing anything. The GFP_ATOMIC flag was
> inherited from how the bucket table was allocated prior to the
> convertion to the new hash table but you are right, it can't be
> needed since the table protection was converted to a mutex.
> Using GFP_KERNEL will have a better chance of succeeding.
> 
Right, I was wondering why it was atomic in the first place and couldn't find a
good reason from the code :-)
But that explains it.

Cheers,
 Nik

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Tue, 05 Aug 2014 07:50:07 +0200

> [PATCH net-next] netlink: fix lockdep splats
> 
> With netlink_lookup() conversion to RCU, we need to use appropriate
> rcu dereference in netlink_seq_socket_idx() & netlink_seq_next()
> 
> Reported-by: Sasha Levin <sasha.levin@oracle.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Fixes: e341694e3eb57fc ("netlink: Convert netlink_lookup() to use RCU protected hash table")

Applied, thanks Eric.

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[David Miller]

From: Eric Dumazet <eric.dumazet-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Date: Tue, 05 Aug 2014 07:50:07 +0200

> [PATCH net-next] netlink: fix lockdep splats
> 
> With netlink_lookup() conversion to RCU, we need to use appropriate
> rcu dereference in netlink_seq_socket_idx() & netlink_seq_next()
> 
> Reported-by: Sasha Levin <sasha.levin-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> Signed-off-by: Eric Dumazet <edumazet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> Fixes: e341694e3eb57fc ("netlink: Convert netlink_lookup() to use RCU protected hash table")

Applied, thanks Eric.

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Eric Dumazet]

On Mon, 2014-08-04 at 19:58 -0700, David Miller wrote:
> From: Sasha Levin <sasha.levin@oracle.com>
> Date: Mon, 04 Aug 2014 22:10:19 -0400
> 
> > On 08/02/2014 05:47 AM, Thomas Graf wrote:
> >>  static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
> >> -	__acquires(nl_table_lock)
> >>  {
> >> -	read_lock(&nl_table_lock);
> >> +	rcu_read_lock();
> >>  	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
> >>  }
> > 
> > I'm not sure how you expect this code to work. You're replacing a local lock
> > with a RCU critical section. Imagine you're doing spin_lock() and just going
> > back to userspace.
> > 
> > It's quite easy to trigger this issue:
> 
> I think he expected the end of the seq sequence to drop the RCU lock,
> via netlink_seq_stop().
> --

Yes, two places use rht_dereference() instead of rht_dereference_rcu()

[PATCH net-next] netlink: fix lockdep splats

With netlink_lookup() conversion to RCU, we need to use appropriate
rcu dereference in netlink_seq_socket_idx() & netlink_seq_next()

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: 
Fixes: e341694e3eb57fc ("netlink: Convert netlink_lookup() to use RCU protected hash table")
---
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0b89ca51a3af..479a344563d8 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2899,7 +2899,7 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 
 	for (i = 0; i < MAX_LINKS; i++) {
 		struct rhashtable *ht = &nl_table[i].hash;
-		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+		const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
 
 		for (j = 0; j < tbl->size; j++) {
 			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
@@ -2950,7 +2950,7 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	do {
 		struct rhashtable *ht = &nl_table[i].hash;
-		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+		const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
 
 		for (; j < tbl->size; j++) {
 			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Eric Dumazet]

On Mon, 2014-08-04 at 19:58 -0700, David Miller wrote:
> From: Sasha Levin <sasha.levin-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> Date: Mon, 04 Aug 2014 22:10:19 -0400
> 
> > On 08/02/2014 05:47 AM, Thomas Graf wrote:
> >>  static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
> >> -	__acquires(nl_table_lock)
> >>  {
> >> -	read_lock(&nl_table_lock);
> >> +	rcu_read_lock();
> >>  	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
> >>  }
> > 
> > I'm not sure how you expect this code to work. You're replacing a local lock
> > with a RCU critical section. Imagine you're doing spin_lock() and just going
> > back to userspace.
> > 
> > It's quite easy to trigger this issue:
> 
> I think he expected the end of the seq sequence to drop the RCU lock,
> via netlink_seq_stop().
> --

Yes, two places use rht_dereference() instead of rht_dereference_rcu()

[PATCH net-next] netlink: fix lockdep splats

With netlink_lookup() conversion to RCU, we need to use appropriate
rcu dereference in netlink_seq_socket_idx() & netlink_seq_next()

Reported-by: Sasha Levin <sasha.levin-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
Signed-off-by: Eric Dumazet <edumazet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: 
Fixes: e341694e3eb57fc ("netlink: Convert netlink_lookup() to use RCU protected hash table")
---
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0b89ca51a3af..479a344563d8 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2899,7 +2899,7 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 
 	for (i = 0; i < MAX_LINKS; i++) {
 		struct rhashtable *ht = &nl_table[i].hash;
-		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+		const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
 
 		for (j = 0; j < tbl->size; j++) {
 			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
@@ -2950,7 +2950,7 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	do {
 		struct rhashtable *ht = &nl_table[i].hash;
-		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+		const struct bucket_table *tbl = rht_dereference_rcu(ht->tbl, ht);
 
 		for (; j < tbl->size; j++) {
 			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[David Miller]

From: Sasha Levin <sasha.levin@oracle.com>
Date: Mon, 04 Aug 2014 22:10:19 -0400

> On 08/02/2014 05:47 AM, Thomas Graf wrote:
>>  static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
>> -	__acquires(nl_table_lock)
>>  {
>> -	read_lock(&nl_table_lock);
>> +	rcu_read_lock();
>>  	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
>>  }
> 
> I'm not sure how you expect this code to work. You're replacing a local lock
> with a RCU critical section. Imagine you're doing spin_lock() and just going
> back to userspace.
> 
> It's quite easy to trigger this issue:

I think he expected the end of the seq sequence to drop the RCU lock,
via netlink_seq_stop().

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[David Miller]

From: Sasha Levin <sasha.levin-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
Date: Mon, 04 Aug 2014 22:10:19 -0400

> On 08/02/2014 05:47 AM, Thomas Graf wrote:
>>  static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
>> -	__acquires(nl_table_lock)
>>  {
>> -	read_lock(&nl_table_lock);
>> +	rcu_read_lock();
>>  	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
>>  }
> 
> I'm not sure how you expect this code to work. You're replacing a local lock
> with a RCU critical section. Imagine you're doing spin_lock() and just going
> back to userspace.
> 
> It's quite easy to trigger this issue:

I think he expected the end of the seq sequence to drop the RCU lock,
via netlink_seq_stop().

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Sasha Levin]

On 08/02/2014 05:47 AM, Thomas Graf wrote:
>  static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
> -	__acquires(nl_table_lock)
>  {
> -	read_lock(&nl_table_lock);
> +	rcu_read_lock();
>  	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
>  }

I'm not sure how you expect this code to work. You're replacing a local lock
with a RCU critical section. Imagine you're doing spin_lock() and just going
back to userspace.

It's quite easy to trigger this issue:

[  531.479773] ===============================
[  531.482951] [ INFO: suspicious RCU usage. ]
[  531.485512] 3.16.0-next-20140804-sasha-00029-gcb12d07 #995 Not tainted
[  531.489198] -------------------------------
[  531.491518] net/netlink/af_netlink.c:2953 suspicious rcu_dereference_protected() usage!
[  531.495781]
[  531.495781] other info that might help us debug this:
[  531.495781]
[  531.499094]
[  531.499094] rcu_scheduler_active = 1, debug_locks = 1
[  531.502685] 3 locks held by trinity-c490/9673:
[  531.505179] #0: (&f->f_pos_lock){+.+.+.}, at: __fdget_pos (fs/file.c:714)
[  531.510057] #1: (&p->lock){+.+.+.}, at: seq_lseek (fs/seq_file.c:322)
[  531.514819] #2: (rcu_read_lock){......}, at: netlink_seq_start (net/netlink/af_netlink.c:2923)
[  531.517956]
[  531.517956] stack backtrace:
[  531.519054] CPU: 7 PID: 9673 Comm: cat Not tainted 3.16.0-next-20140804-sasha-00029-gcb12d07 #995
[  531.521526]  0000000000000000 00000000917b9e45 ffff881efe493e20 ffffffffa55825a1
[  531.523616]  ffff881efebeb000 ffff881efe493e50 ffffffffa21d3a75 ffffffffa81ce2c0
[  531.527426]  0000000000000002 ffff8807cb581d90 ffff880fa3da8000 ffff881efe493ea0
[  531.532068] Call Trace:
[  531.533595] dump_stack (lib/dump_stack.c:52)
[  531.536398] lockdep_rcu_suspicious (kernel/locking/lockdep.c:4259)
[  531.537934] netlink_seq_next (net/netlink/af_netlink.c:2953 (discriminator 5))
[  531.539355] traverse (fs/seq_file.c:142)
[  531.541241] ? mutex_lock_nested (./arch/x86/include/asm/preempt.h:98 kernel/locking/mutex.c:567 kernel/locking/mutex.c:584)
[  531.544797] seq_lseek (fs/seq_file.c:331 (discriminator 1))
[  531.547485] proc_reg_llseek (fs/proc/inode.c:197)
[  531.549904] SyS_lseek (fs/read_write.c:264 fs/read_write.c:289 fs/read_write.c:280)
[  531.552190] tracesys (arch/x86/kernel/entry_64.S:541)

I'd suggest testing any RCU related patches with CONFIG_PROVE_RCU in the future.


Thanks,
Sasha

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Sasha Levin]

On 08/02/2014 05:47 AM, Thomas Graf wrote:
>  static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
> -	__acquires(nl_table_lock)
>  {
> -	read_lock(&nl_table_lock);
> +	rcu_read_lock();
>  	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
>  }

I'm not sure how you expect this code to work. You're replacing a local lock
with a RCU critical section. Imagine you're doing spin_lock() and just going
back to userspace.

It's quite easy to trigger this issue:

[  531.479773] ===============================
[  531.482951] [ INFO: suspicious RCU usage. ]
[  531.485512] 3.16.0-next-20140804-sasha-00029-gcb12d07 #995 Not tainted
[  531.489198] -------------------------------
[  531.491518] net/netlink/af_netlink.c:2953 suspicious rcu_dereference_protected() usage!
[  531.495781]
[  531.495781] other info that might help us debug this:
[  531.495781]
[  531.499094]
[  531.499094] rcu_scheduler_active = 1, debug_locks = 1
[  531.502685] 3 locks held by trinity-c490/9673:
[  531.505179] #0: (&f->f_pos_lock){+.+.+.}, at: __fdget_pos (fs/file.c:714)
[  531.510057] #1: (&p->lock){+.+.+.}, at: seq_lseek (fs/seq_file.c:322)
[  531.514819] #2: (rcu_read_lock){......}, at: netlink_seq_start (net/netlink/af_netlink.c:2923)
[  531.517956]
[  531.517956] stack backtrace:
[  531.519054] CPU: 7 PID: 9673 Comm: cat Not tainted 3.16.0-next-20140804-sasha-00029-gcb12d07 #995
[  531.521526]  0000000000000000 00000000917b9e45 ffff881efe493e20 ffffffffa55825a1
[  531.523616]  ffff881efebeb000 ffff881efe493e50 ffffffffa21d3a75 ffffffffa81ce2c0
[  531.527426]  0000000000000002 ffff8807cb581d90 ffff880fa3da8000 ffff881efe493ea0
[  531.532068] Call Trace:
[  531.533595] dump_stack (lib/dump_stack.c:52)
[  531.536398] lockdep_rcu_suspicious (kernel/locking/lockdep.c:4259)
[  531.537934] netlink_seq_next (net/netlink/af_netlink.c:2953 (discriminator 5))
[  531.539355] traverse (fs/seq_file.c:142)
[  531.541241] ? mutex_lock_nested (./arch/x86/include/asm/preempt.h:98 kernel/locking/mutex.c:567 kernel/locking/mutex.c:584)
[  531.544797] seq_lseek (fs/seq_file.c:331 (discriminator 1))
[  531.547485] proc_reg_llseek (fs/proc/inode.c:197)
[  531.549904] SyS_lseek (fs/read_write.c:264 fs/read_write.c:289 fs/read_write.c:280)
[  531.552190] tracesys (arch/x86/kernel/entry_64.S:541)

I'd suggest testing any RCU related patches with CONFIG_PROVE_RCU in the future.


Thanks,
Sasha

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Nikolay Aleksandrov]

On 08/02/2014 11:47 AM, Thomas Graf wrote:
> Heavy Netlink users such as Open vSwitch spend a considerable amount of
> time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
> RCU relieves the lock contention.
> 
> Makes use of the new resizable hash table to avoid locking on the
> lookup.
> 
> The hash table will grow if entries exceeds 75% of table size up to a
> total table size of 64K. It will automatically shrink if usage falls
> below 30%.
> 
> Also splits nl_table_lock into a separate mutex to protect hash table
> mutations and allow synchronize_rcu() to sleep while waiting for readers
> during expansion and shrinking.
> 
> Before:
>    9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
>    6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
>    6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
>    6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
>    4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
>    4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
>    3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
>    2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
> 
> After:
>   15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
>    8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
>    7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
>    5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
>    4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
>    4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
>    3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
>    [...]
>    0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
> 
> Signed-off-by: Thomas Graf <tgraf@suug.ch>
> ---
>  net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
>  net/netlink/af_netlink.h |  18 +--
>  net/netlink/diag.c       |  11 +-
>  3 files changed, 119 insertions(+), 195 deletions(-)
> 

Reviewed-by: Nikolay Aleksandrov <nikolay@redhat.com>

Re: [PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Nikolay Aleksandrov]

On 08/02/2014 11:47 AM, Thomas Graf wrote:
> Heavy Netlink users such as Open vSwitch spend a considerable amount of
> time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
> RCU relieves the lock contention.
> 
> Makes use of the new resizable hash table to avoid locking on the
> lookup.
> 
> The hash table will grow if entries exceeds 75% of table size up to a
> total table size of 64K. It will automatically shrink if usage falls
> below 30%.
> 
> Also splits nl_table_lock into a separate mutex to protect hash table
> mutations and allow synchronize_rcu() to sleep while waiting for readers
> during expansion and shrinking.
> 
> Before:
>    9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
>    6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
>    6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
>    6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
>    4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
>    4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
>    3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
>    2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
> 
> After:
>   15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
>    8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
>    7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
>    5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
>    4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
>    4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
>    3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
>    [...]
>    0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
> 
> Signed-off-by: Thomas Graf <tgraf-G/eBtMaohhA@public.gmane.org>
> ---
>  net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
>  net/netlink/af_netlink.h |  18 +--
>  net/netlink/diag.c       |  11 +-
>  3 files changed, 119 insertions(+), 195 deletions(-)
> 

Reviewed-by: Nikolay Aleksandrov <nikolay-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

[PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

Heavy Netlink users such as Open vSwitch spend a considerable amount of
time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
RCU relieves the lock contention.

Makes use of the new resizable hash table to avoid locking on the
lookup.

The hash table will grow if entries exceeds 75% of table size up to a
total table size of 64K. It will automatically shrink if usage falls
below 30%.

Also splits nl_table_lock into a separate mutex to protect hash table
mutations and allow synchronize_rcu() to sleep while waiting for readers
during expansion and shrinking.

Before:
   9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
   4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
   3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2

After:
  15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
   3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
   [...]
   0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup

Signed-off-by: Thomas Graf <tgraf@suug.ch>
---
 net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
 net/netlink/af_netlink.h |  18 +--
 net/netlink/diag.c       |  11 +-
 3 files changed, 119 insertions(+), 195 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index ce82722..0b89ca5 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -58,7 +58,9 @@
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>
 #include <linux/if_arp.h>
+#include <linux/rhashtable.h>
 #include <asm/cacheflush.h>
+#include <linux/hash.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -100,6 +102,18 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 #define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
 
+/* Protects netlink socket hash table mutations */
+DEFINE_MUTEX(nl_sk_hash_lock);
+
+static int lockdep_nl_sk_hash_is_held(void)
+{
+#ifdef CONFIG_LOCKDEP
+	return (debug_locks) ? lockdep_is_held(&nl_sk_hash_lock) : 1;
+#else
+	return 1;
+#endif
+}
+
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static DEFINE_SPINLOCK(netlink_tap_lock);
@@ -110,11 +124,6 @@ static inline u32 netlink_group_mask(u32 group)
 	return group ? 1 << (group - 1) : 0;
 }
 
-static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u32 portid)
-{
-	return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
-}
-
 int netlink_add_tap(struct netlink_tap *nt)
 {
 	if (unlikely(nt->dev->type != ARPHRD_NETLINK))
@@ -983,105 +992,48 @@ netlink_unlock_table(void)
 		wake_up(&nl_table_wait);
 }
 
-static bool netlink_compare(struct net *net, struct sock *sk)
-{
-	return net_eq(sock_net(sk), net);
-}
-
-static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
+struct netlink_compare_arg
 {
-	struct netlink_table *table = &nl_table[protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *sk;
-
-	read_lock(&nl_table_lock);
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(sk, head) {
-		if (table->compare(net, sk) &&
-		    (nlk_sk(sk)->portid == portid)) {
-			sock_hold(sk);
-			goto found;
-		}
-	}
-	sk = NULL;
-found:
-	read_unlock(&nl_table_lock);
-	return sk;
-}
+	struct net *net;
+	u32 portid;
+};
 
-static struct hlist_head *nl_portid_hash_zalloc(size_t size)
+static bool netlink_compare(void *ptr, void *arg)
 {
-	if (size <= PAGE_SIZE)
-		return kzalloc(size, GFP_ATOMIC);
-	else
-		return (struct hlist_head *)
-			__get_free_pages(GFP_ATOMIC | __GFP_ZERO,
-					 get_order(size));
-}
+	struct netlink_compare_arg *x = arg;
+	struct sock *sk = ptr;
 
-static void nl_portid_hash_free(struct hlist_head *table, size_t size)
-{
-	if (size <= PAGE_SIZE)
-		kfree(table);
-	else
-		free_pages((unsigned long)table, get_order(size));
+	return nlk_sk(sk)->portid == x->portid &&
+	       net_eq(sock_net(sk), x->net);
 }
 
-static int nl_portid_hash_rehash(struct nl_portid_hash *hash, int grow)
+static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
+				     struct net *net)
 {
-	unsigned int omask, mask, shift;
-	size_t osize, size;
-	struct hlist_head *otable, *table;
-	int i;
-
-	omask = mask = hash->mask;
-	osize = size = (mask + 1) * sizeof(*table);
-	shift = hash->shift;
-
-	if (grow) {
-		if (++shift > hash->max_shift)
-			return 0;
-		mask = mask * 2 + 1;
-		size *= 2;
-	}
+	struct netlink_compare_arg arg = {
+		.net = net,
+		.portid = portid,
+	};
+	u32 hash;
 
-	table = nl_portid_hash_zalloc(size);
-	if (!table)
-		return 0;
+	hash = rhashtable_hashfn(&table->hash, &portid, sizeof(portid));
 
-	otable = hash->table;
-	hash->table = table;
-	hash->mask = mask;
-	hash->shift = shift;
-	get_random_bytes(&hash->rnd, sizeof(hash->rnd));
-
-	for (i = 0; i <= omask; i++) {
-		struct sock *sk;
-		struct hlist_node *tmp;
-
-		sk_for_each_safe(sk, tmp, &otable[i])
-			__sk_add_node(sk, nl_portid_hashfn(hash, nlk_sk(sk)->portid));
-	}
-
-	nl_portid_hash_free(otable, osize);
-	hash->rehash_time = jiffies + 10 * 60 * HZ;
-	return 1;
+	return rhashtable_lookup_compare(&table->hash, hash,
+					 &netlink_compare, &arg);
 }
 
-static inline int nl_portid_hash_dilute(struct nl_portid_hash *hash, int len)
+static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
 {
-	int avg = hash->entries >> hash->shift;
-
-	if (unlikely(avg > 1) && nl_portid_hash_rehash(hash, 1))
-		return 1;
+	struct netlink_table *table = &nl_table[protocol];
+	struct sock *sk;
 
-	if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
-		nl_portid_hash_rehash(hash, 0);
-		return 1;
-	}
+	rcu_read_lock();
+	sk = __netlink_lookup(table, portid, net);
+	if (sk)
+		sock_hold(sk);
+	rcu_read_unlock();
 
-	return 0;
+	return sk;
 }
 
 static const struct proto_ops netlink_ops;
@@ -1113,22 +1065,10 @@ netlink_update_listeners(struct sock *sk)
 static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 {
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
 	int err = -EADDRINUSE;
-	struct sock *osk;
-	int len;
 
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	len = 0;
-	sk_for_each(osk, head) {
-		if (table->compare(net, osk) &&
-		    (nlk_sk(osk)->portid == portid))
-			break;
-		len++;
-	}
-	if (osk)
+	mutex_lock(&nl_sk_hash_lock);
+	if (__netlink_lookup(table, portid, net))
 		goto err;
 
 	err = -EBUSY;
@@ -1136,26 +1076,31 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 		goto err;
 
 	err = -ENOMEM;
-	if (BITS_PER_LONG > 32 && unlikely(hash->entries >= UINT_MAX))
+	if (BITS_PER_LONG > 32 && unlikely(table->hash.nelems >= UINT_MAX))
 		goto err;
 
-	if (len && nl_portid_hash_dilute(hash, len))
-		head = nl_portid_hashfn(hash, portid);
-	hash->entries++;
 	nlk_sk(sk)->portid = portid;
-	sk_add_node(sk, head);
+	sock_hold(sk);
+	rhashtable_insert(&table->hash, &nlk_sk(sk)->node, GFP_KERNEL);
 	err = 0;
-
 err:
-	netlink_table_ungrab();
+	mutex_unlock(&nl_sk_hash_lock);
 	return err;
 }
 
 static void netlink_remove(struct sock *sk)
 {
+	struct netlink_table *table;
+
+	mutex_lock(&nl_sk_hash_lock);
+	table = &nl_table[sk->sk_protocol];
+	if (rhashtable_remove(&table->hash, &nlk_sk(sk)->node, GFP_KERNEL)) {
+		WARN_ON(atomic_read(&sk->sk_refcnt) == 1);
+		__sock_put(sk);
+	}
+	mutex_unlock(&nl_sk_hash_lock);
+
 	netlink_table_grab();
-	if (sk_del_node_init(sk))
-		nl_table[sk->sk_protocol].hash.entries--;
 	if (nlk_sk(sk)->subscriptions)
 		__sk_del_bind_node(sk);
 	netlink_table_ungrab();
@@ -1311,6 +1256,9 @@ static int netlink_release(struct socket *sock)
 	}
 	netlink_table_ungrab();
 
+	/* Wait for readers to complete */
+	synchronize_net();
+
 	kfree(nlk->groups);
 	nlk->groups = NULL;
 
@@ -1326,30 +1274,22 @@ static int netlink_autobind(struct socket *sock)
 	struct sock *sk = sock->sk;
 	struct net *net = sock_net(sk);
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *osk;
 	s32 portid = task_tgid_vnr(current);
 	int err;
 	static s32 rover = -4097;
 
 retry:
 	cond_resched();
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(osk, head) {
-		if (!table->compare(net, osk))
-			continue;
-		if (nlk_sk(osk)->portid == portid) {
-			/* Bind collision, search negative portid values. */
-			portid = rover--;
-			if (rover > -4097)
-				rover = -4097;
-			netlink_table_ungrab();
-			goto retry;
-		}
+	rcu_read_lock();
+	if (__netlink_lookup(table, portid, net)) {
+		/* Bind collision, search negative portid values. */
+		portid = rover--;
+		if (rover > -4097)
+			rover = -4097;
+		rcu_read_unlock();
+		goto retry;
 	}
-	netlink_table_ungrab();
+	rcu_read_unlock();
 
 	err = netlink_insert(sk, net, portid);
 	if (err == -EADDRINUSE)
@@ -2953,14 +2893,18 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 {
 	struct nl_seq_iter *iter = seq->private;
 	int i, j;
+	struct netlink_sock *nlk;
 	struct sock *s;
 	loff_t off = 0;
 
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+		for (j = 0; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				s = (struct sock *)nlk;
 
-		for (j = 0; j <= hash->mask; j++) {
-			sk_for_each(s, &hash->table[j]) {
 				if (sock_net(s) != seq_file_net(seq))
 					continue;
 				if (off == pos) {
@@ -2976,15 +2920,14 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 }
 
 static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(nl_table_lock)
 {
-	read_lock(&nl_table_lock);
+	rcu_read_lock();
 	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
 }
 
 static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct sock *s;
+	struct netlink_sock *nlk;
 	struct nl_seq_iter *iter;
 	struct net *net;
 	int i, j;
@@ -2996,28 +2939,26 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	net = seq_file_net(seq);
 	iter = seq->private;
-	s = v;
-	do {
-		s = sk_next(s);
-	} while (s && !nl_table[s->sk_protocol].compare(net, s));
-	if (s)
-		return s;
+	nlk = v;
+
+	rht_for_each_entry_rcu(nlk, nlk->node.next, node)
+		if (net_eq(sock_net((struct sock *)nlk), net))
+			return nlk;
 
 	i = iter->link;
 	j = iter->hash_idx + 1;
 
 	do {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		for (; j <= hash->mask; j++) {
-			s = sk_head(&hash->table[j]);
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
 
-			while (s && !nl_table[s->sk_protocol].compare(net, s))
-				s = sk_next(s);
-			if (s) {
-				iter->link = i;
-				iter->hash_idx = j;
-				return s;
+		for (; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				if (net_eq(sock_net((struct sock *)nlk), net)) {
+					iter->link = i;
+					iter->hash_idx = j;
+					return nlk;
+				}
 			}
 		}
 
@@ -3028,9 +2969,8 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void netlink_seq_stop(struct seq_file *seq, void *v)
-	__releases(nl_table_lock)
 {
-	read_unlock(&nl_table_lock);
+	rcu_read_unlock();
 }
 
 
@@ -3168,9 +3108,17 @@ static struct pernet_operations __net_initdata netlink_net_ops = {
 static int __init netlink_proto_init(void)
 {
 	int i;
-	unsigned long limit;
-	unsigned int order;
 	int err = proto_register(&netlink_proto, 0);
+	struct rhashtable_params ht_params = {
+		.head_offset = offsetof(struct netlink_sock, node),
+		.key_offset = offsetof(struct netlink_sock, portid),
+		.key_len = sizeof(u32), /* portid */
+		.hashfn = arch_fast_hash,
+		.max_shift = 16, /* 64K */
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+		.mutex_is_held = lockdep_nl_sk_hash_is_held,
+	};
 
 	if (err != 0)
 		goto out;
@@ -3181,32 +3129,13 @@ static int __init netlink_proto_init(void)
 	if (!nl_table)
 		goto panic;
 
-	if (totalram_pages >= (128 * 1024))
-		limit = totalram_pages >> (21 - PAGE_SHIFT);
-	else
-		limit = totalram_pages >> (23 - PAGE_SHIFT);
-
-	order = get_bitmask_order(limit) - 1 + PAGE_SHIFT;
-	limit = (1UL << order) / sizeof(struct hlist_head);
-	order = get_bitmask_order(min(limit, (unsigned long)UINT_MAX)) - 1;
-
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		hash->table = nl_portid_hash_zalloc(1 * sizeof(*hash->table));
-		if (!hash->table) {
-			while (i-- > 0)
-				nl_portid_hash_free(nl_table[i].hash.table,
-						 1 * sizeof(*hash->table));
+		if (rhashtable_init(&nl_table[i].hash, &ht_params) < 0) {
+			while (--i > 0)
+				rhashtable_destroy(&nl_table[i].hash);
 			kfree(nl_table);
 			goto panic;
 		}
-		hash->max_shift = order;
-		hash->shift = 0;
-		hash->mask = 0;
-		hash->rehash_time = jiffies;
-
-		nl_table[i].compare = netlink_compare;
 	}
 
 	INIT_LIST_HEAD(&netlink_tap_all);
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d44..60f631f 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -1,6 +1,7 @@
 #ifndef _AF_NETLINK_H
 #define _AF_NETLINK_H
 
+#include <linux/rhashtable.h>
 #include <net/sock.h>
 
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -47,6 +48,8 @@ struct netlink_sock {
 	struct netlink_ring	tx_ring;
 	atomic_t		mapped;
 #endif /* CONFIG_NETLINK_MMAP */
+
+	struct rhash_head	node;
 };
 
 static inline struct netlink_sock *nlk_sk(struct sock *sk)
@@ -54,21 +57,8 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
 	return container_of(sk, struct netlink_sock, sk);
 }
 
-struct nl_portid_hash {
-	struct hlist_head	*table;
-	unsigned long		rehash_time;
-
-	unsigned int		mask;
-	unsigned int		shift;
-
-	unsigned int		entries;
-	unsigned int		max_shift;
-
-	u32			rnd;
-};
-
 struct netlink_table {
-	struct nl_portid_hash	hash;
+	struct rhashtable	hash;
 	struct hlist_head	mc_list;
 	struct listeners __rcu	*listeners;
 	unsigned int		flags;
diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index 1af29624..7301850 100644
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -4,6 +4,7 @@
 #include <linux/netlink.h>
 #include <linux/sock_diag.h>
 #include <linux/netlink_diag.h>
+#include <linux/rhashtable.h>
 
 #include "af_netlink.h"
 
@@ -101,16 +102,20 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 				int protocol, int s_num)
 {
 	struct netlink_table *tbl = &nl_table[protocol];
-	struct nl_portid_hash *hash = &tbl->hash;
+	struct rhashtable *ht = &tbl->hash;
+	const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
 	struct net *net = sock_net(skb->sk);
 	struct netlink_diag_req *req;
+	struct netlink_sock *nlsk;
 	struct sock *sk;
 	int ret = 0, num = 0, i;
 
 	req = nlmsg_data(cb->nlh);
 
-	for (i = 0; i <= hash->mask; i++) {
-		sk_for_each(sk, &hash->table[i]) {
+	for (i = 0; i < htbl->size; i++) {
+		rht_for_each_entry(nlsk, htbl->buckets[i], ht, node) {
+			sk = (struct sock *)nlsk;
+
 			if (!net_eq(sock_net(sk), net))
 				continue;
 			if (num < s_num) {
-- 
1.9.3

[PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

Heavy Netlink users such as Open vSwitch spend a considerable amount of
time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
RCU relieves the lock contention.

Makes use of the new resizable hash table to avoid locking on the
lookup.

The hash table will grow if entries exceeds 75% of table size up to a
total table size of 64K. It will automatically shrink if usage falls
below 30%.

Also splits nl_table_lock into a separate mutex to protect hash table
mutations and allow synchronize_rcu() to sleep while waiting for readers
during expansion and shrinking.

Before:
   9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
   4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
   3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2

After:
  15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
   3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
   [...]
   0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup

Signed-off-by: Thomas Graf <tgraf-G/eBtMaohhA@public.gmane.org>
---
 net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
 net/netlink/af_netlink.h |  18 +--
 net/netlink/diag.c       |  11 +-
 3 files changed, 119 insertions(+), 195 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index ce82722..0b89ca5 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -58,7 +58,9 @@
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>
 #include <linux/if_arp.h>
+#include <linux/rhashtable.h>
 #include <asm/cacheflush.h>
+#include <linux/hash.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -100,6 +102,18 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 #define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
 
+/* Protects netlink socket hash table mutations */
+DEFINE_MUTEX(nl_sk_hash_lock);
+
+static int lockdep_nl_sk_hash_is_held(void)
+{
+#ifdef CONFIG_LOCKDEP
+	return (debug_locks) ? lockdep_is_held(&nl_sk_hash_lock) : 1;
+#else
+	return 1;
+#endif
+}
+
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static DEFINE_SPINLOCK(netlink_tap_lock);
@@ -110,11 +124,6 @@ static inline u32 netlink_group_mask(u32 group)
 	return group ? 1 << (group - 1) : 0;
 }
 
-static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u32 portid)
-{
-	return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
-}
-
 int netlink_add_tap(struct netlink_tap *nt)
 {
 	if (unlikely(nt->dev->type != ARPHRD_NETLINK))
@@ -983,105 +992,48 @@ netlink_unlock_table(void)
 		wake_up(&nl_table_wait);
 }
 
-static bool netlink_compare(struct net *net, struct sock *sk)
-{
-	return net_eq(sock_net(sk), net);
-}
-
-static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
+struct netlink_compare_arg
 {
-	struct netlink_table *table = &nl_table[protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *sk;
-
-	read_lock(&nl_table_lock);
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(sk, head) {
-		if (table->compare(net, sk) &&
-		    (nlk_sk(sk)->portid == portid)) {
-			sock_hold(sk);
-			goto found;
-		}
-	}
-	sk = NULL;
-found:
-	read_unlock(&nl_table_lock);
-	return sk;
-}
+	struct net *net;
+	u32 portid;
+};
 
-static struct hlist_head *nl_portid_hash_zalloc(size_t size)
+static bool netlink_compare(void *ptr, void *arg)
 {
-	if (size <= PAGE_SIZE)
-		return kzalloc(size, GFP_ATOMIC);
-	else
-		return (struct hlist_head *)
-			__get_free_pages(GFP_ATOMIC | __GFP_ZERO,
-					 get_order(size));
-}
+	struct netlink_compare_arg *x = arg;
+	struct sock *sk = ptr;
 
-static void nl_portid_hash_free(struct hlist_head *table, size_t size)
-{
-	if (size <= PAGE_SIZE)
-		kfree(table);
-	else
-		free_pages((unsigned long)table, get_order(size));
+	return nlk_sk(sk)->portid == x->portid &&
+	       net_eq(sock_net(sk), x->net);
 }
 
-static int nl_portid_hash_rehash(struct nl_portid_hash *hash, int grow)
+static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
+				     struct net *net)
 {
-	unsigned int omask, mask, shift;
-	size_t osize, size;
-	struct hlist_head *otable, *table;
-	int i;
-
-	omask = mask = hash->mask;
-	osize = size = (mask + 1) * sizeof(*table);
-	shift = hash->shift;
-
-	if (grow) {
-		if (++shift > hash->max_shift)
-			return 0;
-		mask = mask * 2 + 1;
-		size *= 2;
-	}
+	struct netlink_compare_arg arg = {
+		.net = net,
+		.portid = portid,
+	};
+	u32 hash;
 
-	table = nl_portid_hash_zalloc(size);
-	if (!table)
-		return 0;
+	hash = rhashtable_hashfn(&table->hash, &portid, sizeof(portid));
 
-	otable = hash->table;
-	hash->table = table;
-	hash->mask = mask;
-	hash->shift = shift;
-	get_random_bytes(&hash->rnd, sizeof(hash->rnd));
-
-	for (i = 0; i <= omask; i++) {
-		struct sock *sk;
-		struct hlist_node *tmp;
-
-		sk_for_each_safe(sk, tmp, &otable[i])
-			__sk_add_node(sk, nl_portid_hashfn(hash, nlk_sk(sk)->portid));
-	}
-
-	nl_portid_hash_free(otable, osize);
-	hash->rehash_time = jiffies + 10 * 60 * HZ;
-	return 1;
+	return rhashtable_lookup_compare(&table->hash, hash,
+					 &netlink_compare, &arg);
 }
 
-static inline int nl_portid_hash_dilute(struct nl_portid_hash *hash, int len)
+static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
 {
-	int avg = hash->entries >> hash->shift;
-
-	if (unlikely(avg > 1) && nl_portid_hash_rehash(hash, 1))
-		return 1;
+	struct netlink_table *table = &nl_table[protocol];
+	struct sock *sk;
 
-	if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
-		nl_portid_hash_rehash(hash, 0);
-		return 1;
-	}
+	rcu_read_lock();
+	sk = __netlink_lookup(table, portid, net);
+	if (sk)
+		sock_hold(sk);
+	rcu_read_unlock();
 
-	return 0;
+	return sk;
 }
 
 static const struct proto_ops netlink_ops;
@@ -1113,22 +1065,10 @@ netlink_update_listeners(struct sock *sk)
 static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 {
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
 	int err = -EADDRINUSE;
-	struct sock *osk;
-	int len;
 
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	len = 0;
-	sk_for_each(osk, head) {
-		if (table->compare(net, osk) &&
-		    (nlk_sk(osk)->portid == portid))
-			break;
-		len++;
-	}
-	if (osk)
+	mutex_lock(&nl_sk_hash_lock);
+	if (__netlink_lookup(table, portid, net))
 		goto err;
 
 	err = -EBUSY;
@@ -1136,26 +1076,31 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 		goto err;
 
 	err = -ENOMEM;
-	if (BITS_PER_LONG > 32 && unlikely(hash->entries >= UINT_MAX))
+	if (BITS_PER_LONG > 32 && unlikely(table->hash.nelems >= UINT_MAX))
 		goto err;
 
-	if (len && nl_portid_hash_dilute(hash, len))
-		head = nl_portid_hashfn(hash, portid);
-	hash->entries++;
 	nlk_sk(sk)->portid = portid;
-	sk_add_node(sk, head);
+	sock_hold(sk);
+	rhashtable_insert(&table->hash, &nlk_sk(sk)->node, GFP_KERNEL);
 	err = 0;
-
 err:
-	netlink_table_ungrab();
+	mutex_unlock(&nl_sk_hash_lock);
 	return err;
 }
 
 static void netlink_remove(struct sock *sk)
 {
+	struct netlink_table *table;
+
+	mutex_lock(&nl_sk_hash_lock);
+	table = &nl_table[sk->sk_protocol];
+	if (rhashtable_remove(&table->hash, &nlk_sk(sk)->node, GFP_KERNEL)) {
+		WARN_ON(atomic_read(&sk->sk_refcnt) == 1);
+		__sock_put(sk);
+	}
+	mutex_unlock(&nl_sk_hash_lock);
+
 	netlink_table_grab();
-	if (sk_del_node_init(sk))
-		nl_table[sk->sk_protocol].hash.entries--;
 	if (nlk_sk(sk)->subscriptions)
 		__sk_del_bind_node(sk);
 	netlink_table_ungrab();
@@ -1311,6 +1256,9 @@ static int netlink_release(struct socket *sock)
 	}
 	netlink_table_ungrab();
 
+	/* Wait for readers to complete */
+	synchronize_net();
+
 	kfree(nlk->groups);
 	nlk->groups = NULL;
 
@@ -1326,30 +1274,22 @@ static int netlink_autobind(struct socket *sock)
 	struct sock *sk = sock->sk;
 	struct net *net = sock_net(sk);
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *osk;
 	s32 portid = task_tgid_vnr(current);
 	int err;
 	static s32 rover = -4097;
 
 retry:
 	cond_resched();
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(osk, head) {
-		if (!table->compare(net, osk))
-			continue;
-		if (nlk_sk(osk)->portid == portid) {
-			/* Bind collision, search negative portid values. */
-			portid = rover--;
-			if (rover > -4097)
-				rover = -4097;
-			netlink_table_ungrab();
-			goto retry;
-		}
+	rcu_read_lock();
+	if (__netlink_lookup(table, portid, net)) {
+		/* Bind collision, search negative portid values. */
+		portid = rover--;
+		if (rover > -4097)
+			rover = -4097;
+		rcu_read_unlock();
+		goto retry;
 	}
-	netlink_table_ungrab();
+	rcu_read_unlock();
 
 	err = netlink_insert(sk, net, portid);
 	if (err == -EADDRINUSE)
@@ -2953,14 +2893,18 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 {
 	struct nl_seq_iter *iter = seq->private;
 	int i, j;
+	struct netlink_sock *nlk;
 	struct sock *s;
 	loff_t off = 0;
 
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+		for (j = 0; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				s = (struct sock *)nlk;
 
-		for (j = 0; j <= hash->mask; j++) {
-			sk_for_each(s, &hash->table[j]) {
 				if (sock_net(s) != seq_file_net(seq))
 					continue;
 				if (off == pos) {
@@ -2976,15 +2920,14 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 }
 
 static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(nl_table_lock)
 {
-	read_lock(&nl_table_lock);
+	rcu_read_lock();
 	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
 }
 
 static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct sock *s;
+	struct netlink_sock *nlk;
 	struct nl_seq_iter *iter;
 	struct net *net;
 	int i, j;
@@ -2996,28 +2939,26 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	net = seq_file_net(seq);
 	iter = seq->private;
-	s = v;
-	do {
-		s = sk_next(s);
-	} while (s && !nl_table[s->sk_protocol].compare(net, s));
-	if (s)
-		return s;
+	nlk = v;
+
+	rht_for_each_entry_rcu(nlk, nlk->node.next, node)
+		if (net_eq(sock_net((struct sock *)nlk), net))
+			return nlk;
 
 	i = iter->link;
 	j = iter->hash_idx + 1;
 
 	do {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		for (; j <= hash->mask; j++) {
-			s = sk_head(&hash->table[j]);
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
 
-			while (s && !nl_table[s->sk_protocol].compare(net, s))
-				s = sk_next(s);
-			if (s) {
-				iter->link = i;
-				iter->hash_idx = j;
-				return s;
+		for (; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				if (net_eq(sock_net((struct sock *)nlk), net)) {
+					iter->link = i;
+					iter->hash_idx = j;
+					return nlk;
+				}
 			}
 		}
 
@@ -3028,9 +2969,8 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void netlink_seq_stop(struct seq_file *seq, void *v)
-	__releases(nl_table_lock)
 {
-	read_unlock(&nl_table_lock);
+	rcu_read_unlock();
 }
 
 
@@ -3168,9 +3108,17 @@ static struct pernet_operations __net_initdata netlink_net_ops = {
 static int __init netlink_proto_init(void)
 {
 	int i;
-	unsigned long limit;
-	unsigned int order;
 	int err = proto_register(&netlink_proto, 0);
+	struct rhashtable_params ht_params = {
+		.head_offset = offsetof(struct netlink_sock, node),
+		.key_offset = offsetof(struct netlink_sock, portid),
+		.key_len = sizeof(u32), /* portid */
+		.hashfn = arch_fast_hash,
+		.max_shift = 16, /* 64K */
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+		.mutex_is_held = lockdep_nl_sk_hash_is_held,
+	};
 
 	if (err != 0)
 		goto out;
@@ -3181,32 +3129,13 @@ static int __init netlink_proto_init(void)
 	if (!nl_table)
 		goto panic;
 
-	if (totalram_pages >= (128 * 1024))
-		limit = totalram_pages >> (21 - PAGE_SHIFT);
-	else
-		limit = totalram_pages >> (23 - PAGE_SHIFT);
-
-	order = get_bitmask_order(limit) - 1 + PAGE_SHIFT;
-	limit = (1UL << order) / sizeof(struct hlist_head);
-	order = get_bitmask_order(min(limit, (unsigned long)UINT_MAX)) - 1;
-
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		hash->table = nl_portid_hash_zalloc(1 * sizeof(*hash->table));
-		if (!hash->table) {
-			while (i-- > 0)
-				nl_portid_hash_free(nl_table[i].hash.table,
-						 1 * sizeof(*hash->table));
+		if (rhashtable_init(&nl_table[i].hash, &ht_params) < 0) {
+			while (--i > 0)
+				rhashtable_destroy(&nl_table[i].hash);
 			kfree(nl_table);
 			goto panic;
 		}
-		hash->max_shift = order;
-		hash->shift = 0;
-		hash->mask = 0;
-		hash->rehash_time = jiffies;
-
-		nl_table[i].compare = netlink_compare;
 	}
 
 	INIT_LIST_HEAD(&netlink_tap_all);
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d44..60f631f 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -1,6 +1,7 @@
 #ifndef _AF_NETLINK_H
 #define _AF_NETLINK_H
 
+#include <linux/rhashtable.h>
 #include <net/sock.h>
 
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -47,6 +48,8 @@ struct netlink_sock {
 	struct netlink_ring	tx_ring;
 	atomic_t		mapped;
 #endif /* CONFIG_NETLINK_MMAP */
+
+	struct rhash_head	node;
 };
 
 static inline struct netlink_sock *nlk_sk(struct sock *sk)
@@ -54,21 +57,8 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
 	return container_of(sk, struct netlink_sock, sk);
 }
 
-struct nl_portid_hash {
-	struct hlist_head	*table;
-	unsigned long		rehash_time;
-
-	unsigned int		mask;
-	unsigned int		shift;
-
-	unsigned int		entries;
-	unsigned int		max_shift;
-
-	u32			rnd;
-};
-
 struct netlink_table {
-	struct nl_portid_hash	hash;
+	struct rhashtable	hash;
 	struct hlist_head	mc_list;
 	struct listeners __rcu	*listeners;
 	unsigned int		flags;
diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index 1af29624..7301850 100644
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -4,6 +4,7 @@
 #include <linux/netlink.h>
 #include <linux/sock_diag.h>
 #include <linux/netlink_diag.h>
+#include <linux/rhashtable.h>
 
 #include "af_netlink.h"
 
@@ -101,16 +102,20 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 				int protocol, int s_num)
 {
 	struct netlink_table *tbl = &nl_table[protocol];
-	struct nl_portid_hash *hash = &tbl->hash;
+	struct rhashtable *ht = &tbl->hash;
+	const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
 	struct net *net = sock_net(skb->sk);
 	struct netlink_diag_req *req;
+	struct netlink_sock *nlsk;
 	struct sock *sk;
 	int ret = 0, num = 0, i;
 
 	req = nlmsg_data(cb->nlh);
 
-	for (i = 0; i <= hash->mask; i++) {
-		sk_for_each(sk, &hash->table[i]) {
+	for (i = 0; i < htbl->size; i++) {
+		rht_for_each_entry(nlsk, htbl->buckets[i], ht, node) {
+			sk = (struct sock *)nlsk;
+
 			if (!net_eq(sock_net(sk), net))
 				continue;
 			if (num < s_num) {
-- 
1.9.3

[PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

Heavy Netlink users such as Open vSwitch spend a considerable amount of
time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
RCU relieves the lock contention.

Makes use of the new resizable hash table to avoid locking on the
lookup.

The hash table will grow if entries exceeds 75% of table size up to a
total table size of 64K. It will automatically shrink if usage falls
below 50%.

Also splits nl_table_lock into a separate spinlock to protect hash table
mutations. This avoids a possible deadlock when the hash table growing
waits on RCU readers to complete via synchronize_rcu() while readers
holding RCU read lock are waiting on the nl_table_lock() to be released
to lock the table for broadcasting.

Before:
   9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
   4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
   3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2

After:
  15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
   3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
   [...]
   0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup

Signed-off-by: Thomas Graf <tgraf@suug.ch>
---
 net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
 net/netlink/af_netlink.h |  18 +--
 net/netlink/diag.c       |  11 +-
 3 files changed, 119 insertions(+), 195 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index ce82722..05b7e5e 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -58,7 +58,9 @@
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>
 #include <linux/if_arp.h>
+#include <linux/rhashtable.h>
 #include <asm/cacheflush.h>
+#include <linux/hash.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -100,6 +102,18 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 #define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
 
+/* Protects netlink socket hash table mutations */
+DEFINE_MUTEX(nl_sk_hash_lock);
+
+static int lockdep_nl_sk_hash_is_held(void)
+{
+#ifdef CONFIG_LOCKDEP
+	return (debug_locks) ? lockdep_is_held(&nl_sk_hash_lock) : 1;
+#else
+	return 1;
+#endif
+}
+
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static DEFINE_SPINLOCK(netlink_tap_lock);
@@ -110,11 +124,6 @@ static inline u32 netlink_group_mask(u32 group)
 	return group ? 1 << (group - 1) : 0;
 }
 
-static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u32 portid)
-{
-	return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
-}
-
 int netlink_add_tap(struct netlink_tap *nt)
 {
 	if (unlikely(nt->dev->type != ARPHRD_NETLINK))
@@ -983,105 +992,48 @@ netlink_unlock_table(void)
 		wake_up(&nl_table_wait);
 }
 
-static bool netlink_compare(struct net *net, struct sock *sk)
-{
-	return net_eq(sock_net(sk), net);
-}
-
-static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
+struct netlink_compare_arg
 {
-	struct netlink_table *table = &nl_table[protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *sk;
-
-	read_lock(&nl_table_lock);
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(sk, head) {
-		if (table->compare(net, sk) &&
-		    (nlk_sk(sk)->portid == portid)) {
-			sock_hold(sk);
-			goto found;
-		}
-	}
-	sk = NULL;
-found:
-	read_unlock(&nl_table_lock);
-	return sk;
-}
+	struct net *net;
+	u32 portid;
+};
 
-static struct hlist_head *nl_portid_hash_zalloc(size_t size)
+static bool netlink_compare(void *ptr, void *arg)
 {
-	if (size <= PAGE_SIZE)
-		return kzalloc(size, GFP_ATOMIC);
-	else
-		return (struct hlist_head *)
-			__get_free_pages(GFP_ATOMIC | __GFP_ZERO,
-					 get_order(size));
-}
+	struct netlink_compare_arg *x = arg;
+	struct sock *sk = ptr;
 
-static void nl_portid_hash_free(struct hlist_head *table, size_t size)
-{
-	if (size <= PAGE_SIZE)
-		kfree(table);
-	else
-		free_pages((unsigned long)table, get_order(size));
+	return nlk_sk(sk)->portid == x->portid &&
+	       net_eq(sock_net(sk), x->net);
 }
 
-static int nl_portid_hash_rehash(struct nl_portid_hash *hash, int grow)
+static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
+				     struct net *net)
 {
-	unsigned int omask, mask, shift;
-	size_t osize, size;
-	struct hlist_head *otable, *table;
-	int i;
-
-	omask = mask = hash->mask;
-	osize = size = (mask + 1) * sizeof(*table);
-	shift = hash->shift;
-
-	if (grow) {
-		if (++shift > hash->max_shift)
-			return 0;
-		mask = mask * 2 + 1;
-		size *= 2;
-	}
+	struct netlink_compare_arg arg = {
+		.net = net,
+		.portid = portid,
+	};
+	u32 hash;
 
-	table = nl_portid_hash_zalloc(size);
-	if (!table)
-		return 0;
+	hash = rhashtable_hashfn(&table->hash, &portid, sizeof(portid));
 
-	otable = hash->table;
-	hash->table = table;
-	hash->mask = mask;
-	hash->shift = shift;
-	get_random_bytes(&hash->rnd, sizeof(hash->rnd));
-
-	for (i = 0; i <= omask; i++) {
-		struct sock *sk;
-		struct hlist_node *tmp;
-
-		sk_for_each_safe(sk, tmp, &otable[i])
-			__sk_add_node(sk, nl_portid_hashfn(hash, nlk_sk(sk)->portid));
-	}
-
-	nl_portid_hash_free(otable, osize);
-	hash->rehash_time = jiffies + 10 * 60 * HZ;
-	return 1;
+	return rhashtable_lookup_compare(&table->hash, hash,
+					 &netlink_compare, &arg);
 }
 
-static inline int nl_portid_hash_dilute(struct nl_portid_hash *hash, int len)
+static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
 {
-	int avg = hash->entries >> hash->shift;
-
-	if (unlikely(avg > 1) && nl_portid_hash_rehash(hash, 1))
-		return 1;
+	struct netlink_table *table = &nl_table[protocol];
+	struct sock *sk;
 
-	if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
-		nl_portid_hash_rehash(hash, 0);
-		return 1;
-	}
+	rcu_read_lock();
+	sk = __netlink_lookup(table, portid, net);
+	if (sk)
+		sock_hold(sk);
+	rcu_read_unlock();
 
-	return 0;
+	return sk;
 }
 
 static const struct proto_ops netlink_ops;
@@ -1113,22 +1065,10 @@ netlink_update_listeners(struct sock *sk)
 static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 {
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
 	int err = -EADDRINUSE;
-	struct sock *osk;
-	int len;
 
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	len = 0;
-	sk_for_each(osk, head) {
-		if (table->compare(net, osk) &&
-		    (nlk_sk(osk)->portid == portid))
-			break;
-		len++;
-	}
-	if (osk)
+	mutex_lock(&nl_sk_hash_lock);
+	if (__netlink_lookup(table, portid, net))
 		goto err;
 
 	err = -EBUSY;
@@ -1136,26 +1076,31 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 		goto err;
 
 	err = -ENOMEM;
-	if (BITS_PER_LONG > 32 && unlikely(hash->entries >= UINT_MAX))
+	if (BITS_PER_LONG > 32 && unlikely(table->hash.nelems >= UINT_MAX))
 		goto err;
 
-	if (len && nl_portid_hash_dilute(hash, len))
-		head = nl_portid_hashfn(hash, portid);
-	hash->entries++;
 	nlk_sk(sk)->portid = portid;
-	sk_add_node(sk, head);
+	sock_hold(sk);
+	rhashtable_insert(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC);
 	err = 0;
-
 err:
-	netlink_table_ungrab();
+	mutex_unlock(&nl_sk_hash_lock);
 	return err;
 }
 
 static void netlink_remove(struct sock *sk)
 {
+	struct netlink_table *table;
+
+	mutex_lock(&nl_sk_hash_lock);
+	table = &nl_table[sk->sk_protocol];
+	if (rhashtable_remove(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC)) {
+		WARN_ON(atomic_read(&sk->sk_refcnt) == 1);
+		__sock_put(sk);
+	}
+	mutex_unlock(&nl_sk_hash_lock);
+
 	netlink_table_grab();
-	if (sk_del_node_init(sk))
-		nl_table[sk->sk_protocol].hash.entries--;
 	if (nlk_sk(sk)->subscriptions)
 		__sk_del_bind_node(sk);
 	netlink_table_ungrab();
@@ -1311,6 +1256,9 @@ static int netlink_release(struct socket *sock)
 	}
 	netlink_table_ungrab();
 
+	/* Wait for readers to complete */
+	synchronize_net();
+
 	kfree(nlk->groups);
 	nlk->groups = NULL;
 
@@ -1326,30 +1274,22 @@ static int netlink_autobind(struct socket *sock)
 	struct sock *sk = sock->sk;
 	struct net *net = sock_net(sk);
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *osk;
 	s32 portid = task_tgid_vnr(current);
 	int err;
 	static s32 rover = -4097;
 
 retry:
 	cond_resched();
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(osk, head) {
-		if (!table->compare(net, osk))
-			continue;
-		if (nlk_sk(osk)->portid == portid) {
-			/* Bind collision, search negative portid values. */
-			portid = rover--;
-			if (rover > -4097)
-				rover = -4097;
-			netlink_table_ungrab();
-			goto retry;
-		}
+	rcu_read_lock();
+	if (__netlink_lookup(table, portid, net)) {
+		/* Bind collision, search negative portid values. */
+		portid = rover--;
+		if (rover > -4097)
+			rover = -4097;
+		rcu_read_unlock();
+		goto retry;
 	}
-	netlink_table_ungrab();
+	rcu_read_unlock();
 
 	err = netlink_insert(sk, net, portid);
 	if (err == -EADDRINUSE)
@@ -2953,14 +2893,18 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 {
 	struct nl_seq_iter *iter = seq->private;
 	int i, j;
+	struct netlink_sock *nlk;
 	struct sock *s;
 	loff_t off = 0;
 
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+		for (j = 0; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				s = (struct sock *)nlk;
 
-		for (j = 0; j <= hash->mask; j++) {
-			sk_for_each(s, &hash->table[j]) {
 				if (sock_net(s) != seq_file_net(seq))
 					continue;
 				if (off == pos) {
@@ -2976,15 +2920,14 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 }
 
 static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(nl_table_lock)
 {
-	read_lock(&nl_table_lock);
+	rcu_read_lock();
 	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
 }
 
 static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct sock *s;
+	struct netlink_sock *nlk;
 	struct nl_seq_iter *iter;
 	struct net *net;
 	int i, j;
@@ -2996,28 +2939,26 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	net = seq_file_net(seq);
 	iter = seq->private;
-	s = v;
-	do {
-		s = sk_next(s);
-	} while (s && !nl_table[s->sk_protocol].compare(net, s));
-	if (s)
-		return s;
+	nlk = v;
+
+	rht_for_each_entry_rcu(nlk, nlk->node.next, node)
+		if (net_eq(sock_net((struct sock *)nlk), net))
+			return nlk;
 
 	i = iter->link;
 	j = iter->hash_idx + 1;
 
 	do {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		for (; j <= hash->mask; j++) {
-			s = sk_head(&hash->table[j]);
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
 
-			while (s && !nl_table[s->sk_protocol].compare(net, s))
-				s = sk_next(s);
-			if (s) {
-				iter->link = i;
-				iter->hash_idx = j;
-				return s;
+		for (; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				if (net_eq(sock_net((struct sock *)nlk), net)) {
+					iter->link = i;
+					iter->hash_idx = j;
+					return nlk;
+				}
 			}
 		}
 
@@ -3028,9 +2969,8 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void netlink_seq_stop(struct seq_file *seq, void *v)
-	__releases(nl_table_lock)
 {
-	read_unlock(&nl_table_lock);
+	rcu_read_unlock();
 }
 
 
@@ -3168,9 +3108,17 @@ static struct pernet_operations __net_initdata netlink_net_ops = {
 static int __init netlink_proto_init(void)
 {
 	int i;
-	unsigned long limit;
-	unsigned int order;
 	int err = proto_register(&netlink_proto, 0);
+	struct rhashtable_params ht_params = {
+		.head_offset = offsetof(struct netlink_sock, node),
+		.key_offset = offsetof(struct netlink_sock, portid),
+		.key_len = sizeof(u32), /* portid */
+		.hashfn = arch_fast_hash,
+		.max_shift = 16, /* 64K */
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+		.mutex_is_held = lockdep_nl_sk_hash_is_held,
+	};
 
 	if (err != 0)
 		goto out;
@@ -3181,32 +3129,13 @@ static int __init netlink_proto_init(void)
 	if (!nl_table)
 		goto panic;
 
-	if (totalram_pages >= (128 * 1024))
-		limit = totalram_pages >> (21 - PAGE_SHIFT);
-	else
-		limit = totalram_pages >> (23 - PAGE_SHIFT);
-
-	order = get_bitmask_order(limit) - 1 + PAGE_SHIFT;
-	limit = (1UL << order) / sizeof(struct hlist_head);
-	order = get_bitmask_order(min(limit, (unsigned long)UINT_MAX)) - 1;
-
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		hash->table = nl_portid_hash_zalloc(1 * sizeof(*hash->table));
-		if (!hash->table) {
-			while (i-- > 0)
-				nl_portid_hash_free(nl_table[i].hash.table,
-						 1 * sizeof(*hash->table));
+		if (rhashtable_init(&nl_table[i].hash, &ht_params) < 0) {
+			while (--i > 0)
+				rhashtable_destroy(&nl_table[i].hash);
 			kfree(nl_table);
 			goto panic;
 		}
-		hash->max_shift = order;
-		hash->shift = 0;
-		hash->mask = 0;
-		hash->rehash_time = jiffies;
-
-		nl_table[i].compare = netlink_compare;
 	}
 
 	INIT_LIST_HEAD(&netlink_tap_all);
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d44..60f631f 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -1,6 +1,7 @@
 #ifndef _AF_NETLINK_H
 #define _AF_NETLINK_H
 
+#include <linux/rhashtable.h>
 #include <net/sock.h>
 
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -47,6 +48,8 @@ struct netlink_sock {
 	struct netlink_ring	tx_ring;
 	atomic_t		mapped;
 #endif /* CONFIG_NETLINK_MMAP */
+
+	struct rhash_head	node;
 };
 
 static inline struct netlink_sock *nlk_sk(struct sock *sk)
@@ -54,21 +57,8 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
 	return container_of(sk, struct netlink_sock, sk);
 }
 
-struct nl_portid_hash {
-	struct hlist_head	*table;
-	unsigned long		rehash_time;
-
-	unsigned int		mask;
-	unsigned int		shift;
-
-	unsigned int		entries;
-	unsigned int		max_shift;
-
-	u32			rnd;
-};
-
 struct netlink_table {
-	struct nl_portid_hash	hash;
+	struct rhashtable	hash;
 	struct hlist_head	mc_list;
 	struct listeners __rcu	*listeners;
 	unsigned int		flags;
diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index 1af29624..7301850 100644
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -4,6 +4,7 @@
 #include <linux/netlink.h>
 #include <linux/sock_diag.h>
 #include <linux/netlink_diag.h>
+#include <linux/rhashtable.h>
 
 #include "af_netlink.h"
 
@@ -101,16 +102,20 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 				int protocol, int s_num)
 {
 	struct netlink_table *tbl = &nl_table[protocol];
-	struct nl_portid_hash *hash = &tbl->hash;
+	struct rhashtable *ht = &tbl->hash;
+	const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
 	struct net *net = sock_net(skb->sk);
 	struct netlink_diag_req *req;
+	struct netlink_sock *nlsk;
 	struct sock *sk;
 	int ret = 0, num = 0, i;
 
 	req = nlmsg_data(cb->nlh);
 
-	for (i = 0; i <= hash->mask; i++) {
-		sk_for_each(sk, &hash->table[i]) {
+	for (i = 0; i < htbl->size; i++) {
+		rht_for_each_entry(nlsk, htbl->buckets[i], ht, node) {
+			sk = (struct sock *)nlsk;
+
 			if (!net_eq(sock_net(sk), net))
 				continue;
 			if (num < s_num) {
-- 
1.9.3

[PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

Heavy Netlink users such as Open vSwitch spend a considerable amount of
time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
RCU relieves the lock contention.

Makes use of the new resizable hash table to avoid locking on the
lookup.

The hash table will grow if entries exceeds 75% of table size up to a
total table size of 64K. It will automatically shrink if usage falls
below 50%.

Also splits nl_table_lock into a separate spinlock to protect hash table
mutations. This avoids a possible deadlock when the hash table growing
waits on RCU readers to complete via synchronize_rcu() while readers
holding RCU read lock are waiting on the nl_table_lock() to be released
to lock the table for broadcasting.

Before:
   9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
   4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
   3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2

After:
  15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
   3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
   [...]
   0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup

Signed-off-by: Thomas Graf <tgraf-G/eBtMaohhA@public.gmane.org>
---
 net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
 net/netlink/af_netlink.h |  18 +--
 net/netlink/diag.c       |  11 +-
 3 files changed, 119 insertions(+), 195 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index ce82722..05b7e5e 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -58,7 +58,9 @@
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>
 #include <linux/if_arp.h>
+#include <linux/rhashtable.h>
 #include <asm/cacheflush.h>
+#include <linux/hash.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -100,6 +102,18 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 #define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
 
+/* Protects netlink socket hash table mutations */
+DEFINE_MUTEX(nl_sk_hash_lock);
+
+static int lockdep_nl_sk_hash_is_held(void)
+{
+#ifdef CONFIG_LOCKDEP
+	return (debug_locks) ? lockdep_is_held(&nl_sk_hash_lock) : 1;
+#else
+	return 1;
+#endif
+}
+
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static DEFINE_SPINLOCK(netlink_tap_lock);
@@ -110,11 +124,6 @@ static inline u32 netlink_group_mask(u32 group)
 	return group ? 1 << (group - 1) : 0;
 }
 
-static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u32 portid)
-{
-	return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
-}
-
 int netlink_add_tap(struct netlink_tap *nt)
 {
 	if (unlikely(nt->dev->type != ARPHRD_NETLINK))
@@ -983,105 +992,48 @@ netlink_unlock_table(void)
 		wake_up(&nl_table_wait);
 }
 
-static bool netlink_compare(struct net *net, struct sock *sk)
-{
-	return net_eq(sock_net(sk), net);
-}
-
-static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
+struct netlink_compare_arg
 {
-	struct netlink_table *table = &nl_table[protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *sk;
-
-	read_lock(&nl_table_lock);
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(sk, head) {
-		if (table->compare(net, sk) &&
-		    (nlk_sk(sk)->portid == portid)) {
-			sock_hold(sk);
-			goto found;
-		}
-	}
-	sk = NULL;
-found:
-	read_unlock(&nl_table_lock);
-	return sk;
-}
+	struct net *net;
+	u32 portid;
+};
 
-static struct hlist_head *nl_portid_hash_zalloc(size_t size)
+static bool netlink_compare(void *ptr, void *arg)
 {
-	if (size <= PAGE_SIZE)
-		return kzalloc(size, GFP_ATOMIC);
-	else
-		return (struct hlist_head *)
-			__get_free_pages(GFP_ATOMIC | __GFP_ZERO,
-					 get_order(size));
-}
+	struct netlink_compare_arg *x = arg;
+	struct sock *sk = ptr;
 
-static void nl_portid_hash_free(struct hlist_head *table, size_t size)
-{
-	if (size <= PAGE_SIZE)
-		kfree(table);
-	else
-		free_pages((unsigned long)table, get_order(size));
+	return nlk_sk(sk)->portid == x->portid &&
+	       net_eq(sock_net(sk), x->net);
 }
 
-static int nl_portid_hash_rehash(struct nl_portid_hash *hash, int grow)
+static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
+				     struct net *net)
 {
-	unsigned int omask, mask, shift;
-	size_t osize, size;
-	struct hlist_head *otable, *table;
-	int i;
-
-	omask = mask = hash->mask;
-	osize = size = (mask + 1) * sizeof(*table);
-	shift = hash->shift;
-
-	if (grow) {
-		if (++shift > hash->max_shift)
-			return 0;
-		mask = mask * 2 + 1;
-		size *= 2;
-	}
+	struct netlink_compare_arg arg = {
+		.net = net,
+		.portid = portid,
+	};
+	u32 hash;
 
-	table = nl_portid_hash_zalloc(size);
-	if (!table)
-		return 0;
+	hash = rhashtable_hashfn(&table->hash, &portid, sizeof(portid));
 
-	otable = hash->table;
-	hash->table = table;
-	hash->mask = mask;
-	hash->shift = shift;
-	get_random_bytes(&hash->rnd, sizeof(hash->rnd));
-
-	for (i = 0; i <= omask; i++) {
-		struct sock *sk;
-		struct hlist_node *tmp;
-
-		sk_for_each_safe(sk, tmp, &otable[i])
-			__sk_add_node(sk, nl_portid_hashfn(hash, nlk_sk(sk)->portid));
-	}
-
-	nl_portid_hash_free(otable, osize);
-	hash->rehash_time = jiffies + 10 * 60 * HZ;
-	return 1;
+	return rhashtable_lookup_compare(&table->hash, hash,
+					 &netlink_compare, &arg);
 }
 
-static inline int nl_portid_hash_dilute(struct nl_portid_hash *hash, int len)
+static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
 {
-	int avg = hash->entries >> hash->shift;
-
-	if (unlikely(avg > 1) && nl_portid_hash_rehash(hash, 1))
-		return 1;
+	struct netlink_table *table = &nl_table[protocol];
+	struct sock *sk;
 
-	if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
-		nl_portid_hash_rehash(hash, 0);
-		return 1;
-	}
+	rcu_read_lock();
+	sk = __netlink_lookup(table, portid, net);
+	if (sk)
+		sock_hold(sk);
+	rcu_read_unlock();
 
-	return 0;
+	return sk;
 }
 
 static const struct proto_ops netlink_ops;
@@ -1113,22 +1065,10 @@ netlink_update_listeners(struct sock *sk)
 static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 {
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
 	int err = -EADDRINUSE;
-	struct sock *osk;
-	int len;
 
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	len = 0;
-	sk_for_each(osk, head) {
-		if (table->compare(net, osk) &&
-		    (nlk_sk(osk)->portid == portid))
-			break;
-		len++;
-	}
-	if (osk)
+	mutex_lock(&nl_sk_hash_lock);
+	if (__netlink_lookup(table, portid, net))
 		goto err;
 
 	err = -EBUSY;
@@ -1136,26 +1076,31 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 		goto err;
 
 	err = -ENOMEM;
-	if (BITS_PER_LONG > 32 && unlikely(hash->entries >= UINT_MAX))
+	if (BITS_PER_LONG > 32 && unlikely(table->hash.nelems >= UINT_MAX))
 		goto err;
 
-	if (len && nl_portid_hash_dilute(hash, len))
-		head = nl_portid_hashfn(hash, portid);
-	hash->entries++;
 	nlk_sk(sk)->portid = portid;
-	sk_add_node(sk, head);
+	sock_hold(sk);
+	rhashtable_insert(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC);
 	err = 0;
-
 err:
-	netlink_table_ungrab();
+	mutex_unlock(&nl_sk_hash_lock);
 	return err;
 }
 
 static void netlink_remove(struct sock *sk)
 {
+	struct netlink_table *table;
+
+	mutex_lock(&nl_sk_hash_lock);
+	table = &nl_table[sk->sk_protocol];
+	if (rhashtable_remove(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC)) {
+		WARN_ON(atomic_read(&sk->sk_refcnt) == 1);
+		__sock_put(sk);
+	}
+	mutex_unlock(&nl_sk_hash_lock);
+
 	netlink_table_grab();
-	if (sk_del_node_init(sk))
-		nl_table[sk->sk_protocol].hash.entries--;
 	if (nlk_sk(sk)->subscriptions)
 		__sk_del_bind_node(sk);
 	netlink_table_ungrab();
@@ -1311,6 +1256,9 @@ static int netlink_release(struct socket *sock)
 	}
 	netlink_table_ungrab();
 
+	/* Wait for readers to complete */
+	synchronize_net();
+
 	kfree(nlk->groups);
 	nlk->groups = NULL;
 
@@ -1326,30 +1274,22 @@ static int netlink_autobind(struct socket *sock)
 	struct sock *sk = sock->sk;
 	struct net *net = sock_net(sk);
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *osk;
 	s32 portid = task_tgid_vnr(current);
 	int err;
 	static s32 rover = -4097;
 
 retry:
 	cond_resched();
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(osk, head) {
-		if (!table->compare(net, osk))
-			continue;
-		if (nlk_sk(osk)->portid == portid) {
-			/* Bind collision, search negative portid values. */
-			portid = rover--;
-			if (rover > -4097)
-				rover = -4097;
-			netlink_table_ungrab();
-			goto retry;
-		}
+	rcu_read_lock();
+	if (__netlink_lookup(table, portid, net)) {
+		/* Bind collision, search negative portid values. */
+		portid = rover--;
+		if (rover > -4097)
+			rover = -4097;
+		rcu_read_unlock();
+		goto retry;
 	}
-	netlink_table_ungrab();
+	rcu_read_unlock();
 
 	err = netlink_insert(sk, net, portid);
 	if (err == -EADDRINUSE)
@@ -2953,14 +2893,18 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 {
 	struct nl_seq_iter *iter = seq->private;
 	int i, j;
+	struct netlink_sock *nlk;
 	struct sock *s;
 	loff_t off = 0;
 
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+		for (j = 0; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				s = (struct sock *)nlk;
 
-		for (j = 0; j <= hash->mask; j++) {
-			sk_for_each(s, &hash->table[j]) {
 				if (sock_net(s) != seq_file_net(seq))
 					continue;
 				if (off == pos) {
@@ -2976,15 +2920,14 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 }
 
 static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(nl_table_lock)
 {
-	read_lock(&nl_table_lock);
+	rcu_read_lock();
 	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
 }
 
 static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct sock *s;
+	struct netlink_sock *nlk;
 	struct nl_seq_iter *iter;
 	struct net *net;
 	int i, j;
@@ -2996,28 +2939,26 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	net = seq_file_net(seq);
 	iter = seq->private;
-	s = v;
-	do {
-		s = sk_next(s);
-	} while (s && !nl_table[s->sk_protocol].compare(net, s));
-	if (s)
-		return s;
+	nlk = v;
+
+	rht_for_each_entry_rcu(nlk, nlk->node.next, node)
+		if (net_eq(sock_net((struct sock *)nlk), net))
+			return nlk;
 
 	i = iter->link;
 	j = iter->hash_idx + 1;
 
 	do {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		for (; j <= hash->mask; j++) {
-			s = sk_head(&hash->table[j]);
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
 
-			while (s && !nl_table[s->sk_protocol].compare(net, s))
-				s = sk_next(s);
-			if (s) {
-				iter->link = i;
-				iter->hash_idx = j;
-				return s;
+		for (; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				if (net_eq(sock_net((struct sock *)nlk), net)) {
+					iter->link = i;
+					iter->hash_idx = j;
+					return nlk;
+				}
 			}
 		}
 
@@ -3028,9 +2969,8 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void netlink_seq_stop(struct seq_file *seq, void *v)
-	__releases(nl_table_lock)
 {
-	read_unlock(&nl_table_lock);
+	rcu_read_unlock();
 }
 
 
@@ -3168,9 +3108,17 @@ static struct pernet_operations __net_initdata netlink_net_ops = {
 static int __init netlink_proto_init(void)
 {
 	int i;
-	unsigned long limit;
-	unsigned int order;
 	int err = proto_register(&netlink_proto, 0);
+	struct rhashtable_params ht_params = {
+		.head_offset = offsetof(struct netlink_sock, node),
+		.key_offset = offsetof(struct netlink_sock, portid),
+		.key_len = sizeof(u32), /* portid */
+		.hashfn = arch_fast_hash,
+		.max_shift = 16, /* 64K */
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+		.mutex_is_held = lockdep_nl_sk_hash_is_held,
+	};
 
 	if (err != 0)
 		goto out;
@@ -3181,32 +3129,13 @@ static int __init netlink_proto_init(void)
 	if (!nl_table)
 		goto panic;
 
-	if (totalram_pages >= (128 * 1024))
-		limit = totalram_pages >> (21 - PAGE_SHIFT);
-	else
-		limit = totalram_pages >> (23 - PAGE_SHIFT);
-
-	order = get_bitmask_order(limit) - 1 + PAGE_SHIFT;
-	limit = (1UL << order) / sizeof(struct hlist_head);
-	order = get_bitmask_order(min(limit, (unsigned long)UINT_MAX)) - 1;
-
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		hash->table = nl_portid_hash_zalloc(1 * sizeof(*hash->table));
-		if (!hash->table) {
-			while (i-- > 0)
-				nl_portid_hash_free(nl_table[i].hash.table,
-						 1 * sizeof(*hash->table));
+		if (rhashtable_init(&nl_table[i].hash, &ht_params) < 0) {
+			while (--i > 0)
+				rhashtable_destroy(&nl_table[i].hash);
 			kfree(nl_table);
 			goto panic;
 		}
-		hash->max_shift = order;
-		hash->shift = 0;
-		hash->mask = 0;
-		hash->rehash_time = jiffies;
-
-		nl_table[i].compare = netlink_compare;
 	}
 
 	INIT_LIST_HEAD(&netlink_tap_all);
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d44..60f631f 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -1,6 +1,7 @@
 #ifndef _AF_NETLINK_H
 #define _AF_NETLINK_H
 
+#include <linux/rhashtable.h>
 #include <net/sock.h>
 
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -47,6 +48,8 @@ struct netlink_sock {
 	struct netlink_ring	tx_ring;
 	atomic_t		mapped;
 #endif /* CONFIG_NETLINK_MMAP */
+
+	struct rhash_head	node;
 };
 
 static inline struct netlink_sock *nlk_sk(struct sock *sk)
@@ -54,21 +57,8 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
 	return container_of(sk, struct netlink_sock, sk);
 }
 
-struct nl_portid_hash {
-	struct hlist_head	*table;
-	unsigned long		rehash_time;
-
-	unsigned int		mask;
-	unsigned int		shift;
-
-	unsigned int		entries;
-	unsigned int		max_shift;
-
-	u32			rnd;
-};
-
 struct netlink_table {
-	struct nl_portid_hash	hash;
+	struct rhashtable	hash;
 	struct hlist_head	mc_list;
 	struct listeners __rcu	*listeners;
 	unsigned int		flags;
diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index 1af29624..7301850 100644
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -4,6 +4,7 @@
 #include <linux/netlink.h>
 #include <linux/sock_diag.h>
 #include <linux/netlink_diag.h>
+#include <linux/rhashtable.h>
 
 #include "af_netlink.h"
 
@@ -101,16 +102,20 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 				int protocol, int s_num)
 {
 	struct netlink_table *tbl = &nl_table[protocol];
-	struct nl_portid_hash *hash = &tbl->hash;
+	struct rhashtable *ht = &tbl->hash;
+	const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
 	struct net *net = sock_net(skb->sk);
 	struct netlink_diag_req *req;
+	struct netlink_sock *nlsk;
 	struct sock *sk;
 	int ret = 0, num = 0, i;
 
 	req = nlmsg_data(cb->nlh);
 
-	for (i = 0; i <= hash->mask; i++) {
-		sk_for_each(sk, &hash->table[i]) {
+	for (i = 0; i < htbl->size; i++) {
+		rht_for_each_entry(nlsk, htbl->buckets[i], ht, node) {
+			sk = (struct sock *)nlsk;
+
 			if (!net_eq(sock_net(sk), net))
 				continue;
 			if (num < s_num) {
-- 
1.9.3

[PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

Heavy Netlink users such as Open vSwitch spend a considerable amount of
time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
RCU relieves the lock contention.

Makes use of the new resizable hash table to avoid locking on the
lookup.

The hash table will grow if entries exceeds 75% of table size up to a
total table size of 64K. It will automatically shrink if usage falls
below 50%.

Also splits nl_table_lock into a separate spinlock to protect hash table
mutations. This avoids a possible deadlock when the hash table growing
waits on RCU readers to complete via synchronize_rcu() while readers
holding RCU read lock are waiting on the nl_table_lock() to be released
to lock the table for broadcasting.

Before:
   9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
   4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
   3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2

After:
  15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
   3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
   [...]
   0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup

Signed-off-by: Thomas Graf <tgraf@suug.ch>
---
 net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
 net/netlink/af_netlink.h |  18 +--
 net/netlink/diag.c       |  11 +-
 3 files changed, 119 insertions(+), 195 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 1b38f7f..0ce1429 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -58,7 +58,9 @@
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>
 #include <linux/if_arp.h>
+#include <linux/rhashtable.h>
 #include <asm/cacheflush.h>
+#include <linux/hash.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -100,6 +102,18 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 #define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
 
+/* Protects netlink socket hash table mutations */
+DEFINE_MUTEX(nl_sk_hash_lock);
+
+static int lockdep_nl_sk_hash_is_held(void)
+{
+#ifdef CONFIG_LOCKDEP
+	return (debug_locks) ? lockdep_is_held(&nl_sk_hash_lock) : 1;
+#else
+	return 1;
+#endif
+}
+
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static DEFINE_SPINLOCK(netlink_tap_lock);
@@ -110,11 +124,6 @@ static inline u32 netlink_group_mask(u32 group)
 	return group ? 1 << (group - 1) : 0;
 }
 
-static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u32 portid)
-{
-	return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
-}
-
 int netlink_add_tap(struct netlink_tap *nt)
 {
 	if (unlikely(nt->dev->type != ARPHRD_NETLINK))
@@ -983,105 +992,48 @@ netlink_unlock_table(void)
 		wake_up(&nl_table_wait);
 }
 
-static bool netlink_compare(struct net *net, struct sock *sk)
-{
-	return net_eq(sock_net(sk), net);
-}
-
-static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
+struct netlink_compare_arg
 {
-	struct netlink_table *table = &nl_table[protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *sk;
-
-	read_lock(&nl_table_lock);
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(sk, head) {
-		if (table->compare(net, sk) &&
-		    (nlk_sk(sk)->portid == portid)) {
-			sock_hold(sk);
-			goto found;
-		}
-	}
-	sk = NULL;
-found:
-	read_unlock(&nl_table_lock);
-	return sk;
-}
+	struct net *net;
+	u32 portid;
+};
 
-static struct hlist_head *nl_portid_hash_zalloc(size_t size)
+static bool netlink_compare(void *ptr, void *arg)
 {
-	if (size <= PAGE_SIZE)
-		return kzalloc(size, GFP_ATOMIC);
-	else
-		return (struct hlist_head *)
-			__get_free_pages(GFP_ATOMIC | __GFP_ZERO,
-					 get_order(size));
-}
+	struct netlink_compare_arg *x = arg;
+	struct sock *sk = ptr;
 
-static void nl_portid_hash_free(struct hlist_head *table, size_t size)
-{
-	if (size <= PAGE_SIZE)
-		kfree(table);
-	else
-		free_pages((unsigned long)table, get_order(size));
+	return nlk_sk(sk)->portid == x->portid &&
+	       net_eq(sock_net(sk), x->net);
 }
 
-static int nl_portid_hash_rehash(struct nl_portid_hash *hash, int grow)
+static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
+				     struct net *net)
 {
-	unsigned int omask, mask, shift;
-	size_t osize, size;
-	struct hlist_head *otable, *table;
-	int i;
-
-	omask = mask = hash->mask;
-	osize = size = (mask + 1) * sizeof(*table);
-	shift = hash->shift;
-
-	if (grow) {
-		if (++shift > hash->max_shift)
-			return 0;
-		mask = mask * 2 + 1;
-		size *= 2;
-	}
+	struct netlink_compare_arg arg = {
+		.net = net,
+		.portid = portid,
+	};
+	u32 hash;
 
-	table = nl_portid_hash_zalloc(size);
-	if (!table)
-		return 0;
+	hash = rhashtable_hashfn(&table->hash, &portid, sizeof(portid));
 
-	otable = hash->table;
-	hash->table = table;
-	hash->mask = mask;
-	hash->shift = shift;
-	get_random_bytes(&hash->rnd, sizeof(hash->rnd));
-
-	for (i = 0; i <= omask; i++) {
-		struct sock *sk;
-		struct hlist_node *tmp;
-
-		sk_for_each_safe(sk, tmp, &otable[i])
-			__sk_add_node(sk, nl_portid_hashfn(hash, nlk_sk(sk)->portid));
-	}
-
-	nl_portid_hash_free(otable, osize);
-	hash->rehash_time = jiffies + 10 * 60 * HZ;
-	return 1;
+	return rhashtable_lookup_compare(&table->hash, hash,
+					 &netlink_compare, &arg);
 }
 
-static inline int nl_portid_hash_dilute(struct nl_portid_hash *hash, int len)
+static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
 {
-	int avg = hash->entries >> hash->shift;
-
-	if (unlikely(avg > 1) && nl_portid_hash_rehash(hash, 1))
-		return 1;
+	struct netlink_table *table = &nl_table[protocol];
+	struct sock *sk;
 
-	if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
-		nl_portid_hash_rehash(hash, 0);
-		return 1;
-	}
+	rcu_read_lock();
+	sk = __netlink_lookup(table, portid, net);
+	if (sk)
+		sock_hold(sk);
+	rcu_read_unlock();
 
-	return 0;
+	return sk;
 }
 
 static const struct proto_ops netlink_ops;
@@ -1113,22 +1065,10 @@ netlink_update_listeners(struct sock *sk)
 static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 {
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
 	int err = -EADDRINUSE;
-	struct sock *osk;
-	int len;
 
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	len = 0;
-	sk_for_each(osk, head) {
-		if (table->compare(net, osk) &&
-		    (nlk_sk(osk)->portid == portid))
-			break;
-		len++;
-	}
-	if (osk)
+	mutex_lock(&nl_sk_hash_lock);
+	if (__netlink_lookup(table, portid, net))
 		goto err;
 
 	err = -EBUSY;
@@ -1136,26 +1076,31 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 		goto err;
 
 	err = -ENOMEM;
-	if (BITS_PER_LONG > 32 && unlikely(hash->entries >= UINT_MAX))
+	if (BITS_PER_LONG > 32 && unlikely(table->hash.nelems >= UINT_MAX))
 		goto err;
 
-	if (len && nl_portid_hash_dilute(hash, len))
-		head = nl_portid_hashfn(hash, portid);
-	hash->entries++;
 	nlk_sk(sk)->portid = portid;
-	sk_add_node(sk, head);
+	sock_hold(sk);
+	rhashtable_insert(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC);
 	err = 0;
-
 err:
-	netlink_table_ungrab();
+	mutex_unlock(&nl_sk_hash_lock);
 	return err;
 }
 
 static void netlink_remove(struct sock *sk)
 {
+	struct netlink_table *table;
+
+	mutex_lock(&nl_sk_hash_lock);
+	table = &nl_table[sk->sk_protocol];
+	if (rhashtable_remove(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC)) {
+		WARN_ON(atomic_read(&sk->sk_refcnt) == 1);
+		__sock_put(sk);
+	}
+	mutex_unlock(&nl_sk_hash_lock);
+
 	netlink_table_grab();
-	if (sk_del_node_init(sk))
-		nl_table[sk->sk_protocol].hash.entries--;
 	if (nlk_sk(sk)->subscriptions)
 		__sk_del_bind_node(sk);
 	netlink_table_ungrab();
@@ -1311,6 +1256,9 @@ static int netlink_release(struct socket *sock)
 	}
 	netlink_table_ungrab();
 
+	/* Wait for readers to complete */
+	synchronize_net();
+
 	kfree(nlk->groups);
 	nlk->groups = NULL;
 
@@ -1326,30 +1274,22 @@ static int netlink_autobind(struct socket *sock)
 	struct sock *sk = sock->sk;
 	struct net *net = sock_net(sk);
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *osk;
 	s32 portid = task_tgid_vnr(current);
 	int err;
 	static s32 rover = -4097;
 
 retry:
 	cond_resched();
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(osk, head) {
-		if (!table->compare(net, osk))
-			continue;
-		if (nlk_sk(osk)->portid == portid) {
-			/* Bind collision, search negative portid values. */
-			portid = rover--;
-			if (rover > -4097)
-				rover = -4097;
-			netlink_table_ungrab();
-			goto retry;
-		}
+	rcu_read_lock();
+	if (__netlink_lookup(table, portid, net)) {
+		/* Bind collision, search negative portid values. */
+		portid = rover--;
+		if (rover > -4097)
+			rover = -4097;
+		rcu_read_unlock();
+		goto retry;
 	}
-	netlink_table_ungrab();
+	rcu_read_unlock();
 
 	err = netlink_insert(sk, net, portid);
 	if (err == -EADDRINUSE)
@@ -2953,14 +2893,18 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 {
 	struct nl_seq_iter *iter = seq->private;
 	int i, j;
+	struct netlink_sock *nlk;
 	struct sock *s;
 	loff_t off = 0;
 
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+		for (j = 0; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				s = (struct sock *)nlk;
 
-		for (j = 0; j <= hash->mask; j++) {
-			sk_for_each(s, &hash->table[j]) {
 				if (sock_net(s) != seq_file_net(seq))
 					continue;
 				if (off == pos) {
@@ -2976,15 +2920,14 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 }
 
 static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(nl_table_lock)
 {
-	read_lock(&nl_table_lock);
+	rcu_read_lock();
 	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
 }
 
 static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct sock *s;
+	struct netlink_sock *nlk;
 	struct nl_seq_iter *iter;
 	struct net *net;
 	int i, j;
@@ -2996,28 +2939,26 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	net = seq_file_net(seq);
 	iter = seq->private;
-	s = v;
-	do {
-		s = sk_next(s);
-	} while (s && !nl_table[s->sk_protocol].compare(net, s));
-	if (s)
-		return s;
+	nlk = v;
+
+	rht_for_each_entry_rcu(nlk, nlk->node.next, node)
+		if (net_eq(sock_net((struct sock *)nlk), net))
+			return nlk;
 
 	i = iter->link;
 	j = iter->hash_idx + 1;
 
 	do {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		for (; j <= hash->mask; j++) {
-			s = sk_head(&hash->table[j]);
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
 
-			while (s && !nl_table[s->sk_protocol].compare(net, s))
-				s = sk_next(s);
-			if (s) {
-				iter->link = i;
-				iter->hash_idx = j;
-				return s;
+		for (; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				if (net_eq(sock_net((struct sock *)nlk), net)) {
+					iter->link = i;
+					iter->hash_idx = j;
+					return nlk;
+				}
 			}
 		}
 
@@ -3028,9 +2969,8 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void netlink_seq_stop(struct seq_file *seq, void *v)
-	__releases(nl_table_lock)
 {
-	read_unlock(&nl_table_lock);
+	rcu_read_unlock();
 }
 
 
@@ -3168,9 +3108,17 @@ static struct pernet_operations __net_initdata netlink_net_ops = {
 static int __init netlink_proto_init(void)
 {
 	int i;
-	unsigned long limit;
-	unsigned int order;
 	int err = proto_register(&netlink_proto, 0);
+	struct rhashtable_params ht_params = {
+		.head_offset = offsetof(struct netlink_sock, node),
+		.key_offset = offsetof(struct netlink_sock, portid),
+		.key_len = sizeof(u32), /* portid */
+		.hashfn = arch_fast_hash,
+		.max_shift = 16, /* 64K */
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+		.mutex_is_held = lockdep_nl_sk_hash_is_held,
+	};
 
 	if (err != 0)
 		goto out;
@@ -3181,32 +3129,13 @@ static int __init netlink_proto_init(void)
 	if (!nl_table)
 		goto panic;
 
-	if (totalram_pages >= (128 * 1024))
-		limit = totalram_pages >> (21 - PAGE_SHIFT);
-	else
-		limit = totalram_pages >> (23 - PAGE_SHIFT);
-
-	order = get_bitmask_order(limit) - 1 + PAGE_SHIFT;
-	limit = (1UL << order) / sizeof(struct hlist_head);
-	order = get_bitmask_order(min(limit, (unsigned long)UINT_MAX)) - 1;
-
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		hash->table = nl_portid_hash_zalloc(1 * sizeof(*hash->table));
-		if (!hash->table) {
-			while (i-- > 0)
-				nl_portid_hash_free(nl_table[i].hash.table,
-						 1 * sizeof(*hash->table));
+		if (rhashtable_init(&nl_table[i].hash, &ht_params) < 0) {
+			while (--i > 0)
+				rhashtable_destroy(&nl_table[i].hash);
 			kfree(nl_table);
 			goto panic;
 		}
-		hash->max_shift = order;
-		hash->shift = 0;
-		hash->mask = 0;
-		hash->rehash_time = jiffies;
-
-		nl_table[i].compare = netlink_compare;
 	}
 
 	INIT_LIST_HEAD(&netlink_tap_all);
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d44..60f631f 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -1,6 +1,7 @@
 #ifndef _AF_NETLINK_H
 #define _AF_NETLINK_H
 
+#include <linux/rhashtable.h>
 #include <net/sock.h>
 
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -47,6 +48,8 @@ struct netlink_sock {
 	struct netlink_ring	tx_ring;
 	atomic_t		mapped;
 #endif /* CONFIG_NETLINK_MMAP */
+
+	struct rhash_head	node;
 };
 
 static inline struct netlink_sock *nlk_sk(struct sock *sk)
@@ -54,21 +57,8 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
 	return container_of(sk, struct netlink_sock, sk);
 }
 
-struct nl_portid_hash {
-	struct hlist_head	*table;
-	unsigned long		rehash_time;
-
-	unsigned int		mask;
-	unsigned int		shift;
-
-	unsigned int		entries;
-	unsigned int		max_shift;
-
-	u32			rnd;
-};
-
 struct netlink_table {
-	struct nl_portid_hash	hash;
+	struct rhashtable	hash;
 	struct hlist_head	mc_list;
 	struct listeners __rcu	*listeners;
 	unsigned int		flags;
diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index 1af29624..7301850 100644
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -4,6 +4,7 @@
 #include <linux/netlink.h>
 #include <linux/sock_diag.h>
 #include <linux/netlink_diag.h>
+#include <linux/rhashtable.h>
 
 #include "af_netlink.h"
 
@@ -101,16 +102,20 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 				int protocol, int s_num)
 {
 	struct netlink_table *tbl = &nl_table[protocol];
-	struct nl_portid_hash *hash = &tbl->hash;
+	struct rhashtable *ht = &tbl->hash;
+	const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
 	struct net *net = sock_net(skb->sk);
 	struct netlink_diag_req *req;
+	struct netlink_sock *nlsk;
 	struct sock *sk;
 	int ret = 0, num = 0, i;
 
 	req = nlmsg_data(cb->nlh);
 
-	for (i = 0; i <= hash->mask; i++) {
-		sk_for_each(sk, &hash->table[i]) {
+	for (i = 0; i < htbl->size; i++) {
+		rht_for_each_entry(nlsk, htbl->buckets[i], ht, node) {
+			sk = (struct sock *)nlsk;
+
 			if (!net_eq(sock_net(sk), net))
 				continue;
 			if (num < s_num) {
-- 
1.9.3

[PATCH net-next 2/3] netlink: Convert netlink_lookup() to use RCU protected hash table

[Thomas Graf]

Heavy Netlink users such as Open vSwitch spend a considerable amount of
time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
RCU relieves the lock contention.

Makes use of the new resizable hash table to avoid locking on the
lookup.

The hash table will grow if entries exceeds 75% of table size up to a
total table size of 64K. It will automatically shrink if usage falls
below 50%.

Also splits nl_table_lock into a separate spinlock to protect hash table
mutations. This avoids a possible deadlock when the hash table growing
waits on RCU readers to complete via synchronize_rcu() while readers
holding RCU read lock are waiting on the nl_table_lock() to be released
to lock the table for broadcasting.

Before:
   9.16%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   6.42%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   6.26%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   6.23%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.79%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup
   4.37%  kpktgend_0  [kernel.kallsyms]  [k] memcpy
   3.60%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   2.69%  kpktgend_0  [kernel.kallsyms]  [k] jhash2

After:
  15.26%  kpktgend_0  [openvswitch]      [k] masked_flow_lookup
   8.12%  kpktgend_0  [pktgen]           [k] pktgen_thread_worker
   7.92%  kpktgend_0  [pktgen]           [k] mod_cur_headers
   5.11%  kpktgend_0  [kernel.kallsyms]  [k] memset
   4.11%  kpktgend_0  [openvswitch]      [k] ovs_flow_extract
   4.06%  kpktgend_0  [kernel.kallsyms]  [k] _raw_spin_lock
   3.90%  kpktgend_0  [kernel.kallsyms]  [k] jhash2
   [...]
   0.67%  kpktgend_0  [kernel.kallsyms]  [k] netlink_lookup

Signed-off-by: Thomas Graf <tgraf-G/eBtMaohhA@public.gmane.org>
---
 net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
 net/netlink/af_netlink.h |  18 +--
 net/netlink/diag.c       |  11 +-
 3 files changed, 119 insertions(+), 195 deletions(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 1b38f7f..0ce1429 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -58,7 +58,9 @@
 #include <linux/mutex.h>
 #include <linux/vmalloc.h>
 #include <linux/if_arp.h>
+#include <linux/rhashtable.h>
 #include <asm/cacheflush.h>
+#include <linux/hash.h>
 
 #include <net/net_namespace.h>
 #include <net/sock.h>
@@ -100,6 +102,18 @@ static atomic_t nl_table_users = ATOMIC_INIT(0);
 
 #define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));
 
+/* Protects netlink socket hash table mutations */
+DEFINE_MUTEX(nl_sk_hash_lock);
+
+static int lockdep_nl_sk_hash_is_held(void)
+{
+#ifdef CONFIG_LOCKDEP
+	return (debug_locks) ? lockdep_is_held(&nl_sk_hash_lock) : 1;
+#else
+	return 1;
+#endif
+}
+
 static ATOMIC_NOTIFIER_HEAD(netlink_chain);
 
 static DEFINE_SPINLOCK(netlink_tap_lock);
@@ -110,11 +124,6 @@ static inline u32 netlink_group_mask(u32 group)
 	return group ? 1 << (group - 1) : 0;
 }
 
-static inline struct hlist_head *nl_portid_hashfn(struct nl_portid_hash *hash, u32 portid)
-{
-	return &hash->table[jhash_1word(portid, hash->rnd) & hash->mask];
-}
-
 int netlink_add_tap(struct netlink_tap *nt)
 {
 	if (unlikely(nt->dev->type != ARPHRD_NETLINK))
@@ -983,105 +992,48 @@ netlink_unlock_table(void)
 		wake_up(&nl_table_wait);
 }
 
-static bool netlink_compare(struct net *net, struct sock *sk)
-{
-	return net_eq(sock_net(sk), net);
-}
-
-static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
+struct netlink_compare_arg
 {
-	struct netlink_table *table = &nl_table[protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *sk;
-
-	read_lock(&nl_table_lock);
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(sk, head) {
-		if (table->compare(net, sk) &&
-		    (nlk_sk(sk)->portid == portid)) {
-			sock_hold(sk);
-			goto found;
-		}
-	}
-	sk = NULL;
-found:
-	read_unlock(&nl_table_lock);
-	return sk;
-}
+	struct net *net;
+	u32 portid;
+};
 
-static struct hlist_head *nl_portid_hash_zalloc(size_t size)
+static bool netlink_compare(void *ptr, void *arg)
 {
-	if (size <= PAGE_SIZE)
-		return kzalloc(size, GFP_ATOMIC);
-	else
-		return (struct hlist_head *)
-			__get_free_pages(GFP_ATOMIC | __GFP_ZERO,
-					 get_order(size));
-}
+	struct netlink_compare_arg *x = arg;
+	struct sock *sk = ptr;
 
-static void nl_portid_hash_free(struct hlist_head *table, size_t size)
-{
-	if (size <= PAGE_SIZE)
-		kfree(table);
-	else
-		free_pages((unsigned long)table, get_order(size));
+	return nlk_sk(sk)->portid == x->portid &&
+	       net_eq(sock_net(sk), x->net);
 }
 
-static int nl_portid_hash_rehash(struct nl_portid_hash *hash, int grow)
+static struct sock *__netlink_lookup(struct netlink_table *table, u32 portid,
+				     struct net *net)
 {
-	unsigned int omask, mask, shift;
-	size_t osize, size;
-	struct hlist_head *otable, *table;
-	int i;
-
-	omask = mask = hash->mask;
-	osize = size = (mask + 1) * sizeof(*table);
-	shift = hash->shift;
-
-	if (grow) {
-		if (++shift > hash->max_shift)
-			return 0;
-		mask = mask * 2 + 1;
-		size *= 2;
-	}
+	struct netlink_compare_arg arg = {
+		.net = net,
+		.portid = portid,
+	};
+	u32 hash;
 
-	table = nl_portid_hash_zalloc(size);
-	if (!table)
-		return 0;
+	hash = rhashtable_hashfn(&table->hash, &portid, sizeof(portid));
 
-	otable = hash->table;
-	hash->table = table;
-	hash->mask = mask;
-	hash->shift = shift;
-	get_random_bytes(&hash->rnd, sizeof(hash->rnd));
-
-	for (i = 0; i <= omask; i++) {
-		struct sock *sk;
-		struct hlist_node *tmp;
-
-		sk_for_each_safe(sk, tmp, &otable[i])
-			__sk_add_node(sk, nl_portid_hashfn(hash, nlk_sk(sk)->portid));
-	}
-
-	nl_portid_hash_free(otable, osize);
-	hash->rehash_time = jiffies + 10 * 60 * HZ;
-	return 1;
+	return rhashtable_lookup_compare(&table->hash, hash,
+					 &netlink_compare, &arg);
 }
 
-static inline int nl_portid_hash_dilute(struct nl_portid_hash *hash, int len)
+static struct sock *netlink_lookup(struct net *net, int protocol, u32 portid)
 {
-	int avg = hash->entries >> hash->shift;
-
-	if (unlikely(avg > 1) && nl_portid_hash_rehash(hash, 1))
-		return 1;
+	struct netlink_table *table = &nl_table[protocol];
+	struct sock *sk;
 
-	if (unlikely(len > avg) && time_after(jiffies, hash->rehash_time)) {
-		nl_portid_hash_rehash(hash, 0);
-		return 1;
-	}
+	rcu_read_lock();
+	sk = __netlink_lookup(table, portid, net);
+	if (sk)
+		sock_hold(sk);
+	rcu_read_unlock();
 
-	return 0;
+	return sk;
 }
 
 static const struct proto_ops netlink_ops;
@@ -1113,22 +1065,10 @@ netlink_update_listeners(struct sock *sk)
 static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 {
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
 	int err = -EADDRINUSE;
-	struct sock *osk;
-	int len;
 
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	len = 0;
-	sk_for_each(osk, head) {
-		if (table->compare(net, osk) &&
-		    (nlk_sk(osk)->portid == portid))
-			break;
-		len++;
-	}
-	if (osk)
+	mutex_lock(&nl_sk_hash_lock);
+	if (__netlink_lookup(table, portid, net))
 		goto err;
 
 	err = -EBUSY;
@@ -1136,26 +1076,31 @@ static int netlink_insert(struct sock *sk, struct net *net, u32 portid)
 		goto err;
 
 	err = -ENOMEM;
-	if (BITS_PER_LONG > 32 && unlikely(hash->entries >= UINT_MAX))
+	if (BITS_PER_LONG > 32 && unlikely(table->hash.nelems >= UINT_MAX))
 		goto err;
 
-	if (len && nl_portid_hash_dilute(hash, len))
-		head = nl_portid_hashfn(hash, portid);
-	hash->entries++;
 	nlk_sk(sk)->portid = portid;
-	sk_add_node(sk, head);
+	sock_hold(sk);
+	rhashtable_insert(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC);
 	err = 0;
-
 err:
-	netlink_table_ungrab();
+	mutex_unlock(&nl_sk_hash_lock);
 	return err;
 }
 
 static void netlink_remove(struct sock *sk)
 {
+	struct netlink_table *table;
+
+	mutex_lock(&nl_sk_hash_lock);
+	table = &nl_table[sk->sk_protocol];
+	if (rhashtable_remove(&table->hash, &nlk_sk(sk)->node, GFP_ATOMIC)) {
+		WARN_ON(atomic_read(&sk->sk_refcnt) == 1);
+		__sock_put(sk);
+	}
+	mutex_unlock(&nl_sk_hash_lock);
+
 	netlink_table_grab();
-	if (sk_del_node_init(sk))
-		nl_table[sk->sk_protocol].hash.entries--;
 	if (nlk_sk(sk)->subscriptions)
 		__sk_del_bind_node(sk);
 	netlink_table_ungrab();
@@ -1311,6 +1256,9 @@ static int netlink_release(struct socket *sock)
 	}
 	netlink_table_ungrab();
 
+	/* Wait for readers to complete */
+	synchronize_net();
+
 	kfree(nlk->groups);
 	nlk->groups = NULL;
 
@@ -1326,30 +1274,22 @@ static int netlink_autobind(struct socket *sock)
 	struct sock *sk = sock->sk;
 	struct net *net = sock_net(sk);
 	struct netlink_table *table = &nl_table[sk->sk_protocol];
-	struct nl_portid_hash *hash = &table->hash;
-	struct hlist_head *head;
-	struct sock *osk;
 	s32 portid = task_tgid_vnr(current);
 	int err;
 	static s32 rover = -4097;
 
 retry:
 	cond_resched();
-	netlink_table_grab();
-	head = nl_portid_hashfn(hash, portid);
-	sk_for_each(osk, head) {
-		if (!table->compare(net, osk))
-			continue;
-		if (nlk_sk(osk)->portid == portid) {
-			/* Bind collision, search negative portid values. */
-			portid = rover--;
-			if (rover > -4097)
-				rover = -4097;
-			netlink_table_ungrab();
-			goto retry;
-		}
+	rcu_read_lock();
+	if (__netlink_lookup(table, portid, net)) {
+		/* Bind collision, search negative portid values. */
+		portid = rover--;
+		if (rover > -4097)
+			rover = -4097;
+		rcu_read_unlock();
+		goto retry;
 	}
-	netlink_table_ungrab();
+	rcu_read_unlock();
 
 	err = netlink_insert(sk, net, portid);
 	if (err == -EADDRINUSE)
@@ -2953,14 +2893,18 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 {
 	struct nl_seq_iter *iter = seq->private;
 	int i, j;
+	struct netlink_sock *nlk;
 	struct sock *s;
 	loff_t off = 0;
 
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
+
+		for (j = 0; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				s = (struct sock *)nlk;
 
-		for (j = 0; j <= hash->mask; j++) {
-			sk_for_each(s, &hash->table[j]) {
 				if (sock_net(s) != seq_file_net(seq))
 					continue;
 				if (off == pos) {
@@ -2976,15 +2920,14 @@ static struct sock *netlink_seq_socket_idx(struct seq_file *seq, loff_t pos)
 }
 
 static void *netlink_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(nl_table_lock)
 {
-	read_lock(&nl_table_lock);
+	rcu_read_lock();
 	return *pos ? netlink_seq_socket_idx(seq, *pos - 1) : SEQ_START_TOKEN;
 }
 
 static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct sock *s;
+	struct netlink_sock *nlk;
 	struct nl_seq_iter *iter;
 	struct net *net;
 	int i, j;
@@ -2996,28 +2939,26 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 
 	net = seq_file_net(seq);
 	iter = seq->private;
-	s = v;
-	do {
-		s = sk_next(s);
-	} while (s && !nl_table[s->sk_protocol].compare(net, s));
-	if (s)
-		return s;
+	nlk = v;
+
+	rht_for_each_entry_rcu(nlk, nlk->node.next, node)
+		if (net_eq(sock_net((struct sock *)nlk), net))
+			return nlk;
 
 	i = iter->link;
 	j = iter->hash_idx + 1;
 
 	do {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		for (; j <= hash->mask; j++) {
-			s = sk_head(&hash->table[j]);
+		struct rhashtable *ht = &nl_table[i].hash;
+		const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
 
-			while (s && !nl_table[s->sk_protocol].compare(net, s))
-				s = sk_next(s);
-			if (s) {
-				iter->link = i;
-				iter->hash_idx = j;
-				return s;
+		for (; j < tbl->size; j++) {
+			rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
+				if (net_eq(sock_net((struct sock *)nlk), net)) {
+					iter->link = i;
+					iter->hash_idx = j;
+					return nlk;
+				}
 			}
 		}
 
@@ -3028,9 +2969,8 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void netlink_seq_stop(struct seq_file *seq, void *v)
-	__releases(nl_table_lock)
 {
-	read_unlock(&nl_table_lock);
+	rcu_read_unlock();
 }
 
 
@@ -3168,9 +3108,17 @@ static struct pernet_operations __net_initdata netlink_net_ops = {
 static int __init netlink_proto_init(void)
 {
 	int i;
-	unsigned long limit;
-	unsigned int order;
 	int err = proto_register(&netlink_proto, 0);
+	struct rhashtable_params ht_params = {
+		.head_offset = offsetof(struct netlink_sock, node),
+		.key_offset = offsetof(struct netlink_sock, portid),
+		.key_len = sizeof(u32), /* portid */
+		.hashfn = arch_fast_hash,
+		.max_shift = 16, /* 64K */
+		.grow_decision = rht_grow_above_75,
+		.shrink_decision = rht_shrink_below_30,
+		.mutex_is_held = lockdep_nl_sk_hash_is_held,
+	};
 
 	if (err != 0)
 		goto out;
@@ -3181,32 +3129,13 @@ static int __init netlink_proto_init(void)
 	if (!nl_table)
 		goto panic;
 
-	if (totalram_pages >= (128 * 1024))
-		limit = totalram_pages >> (21 - PAGE_SHIFT);
-	else
-		limit = totalram_pages >> (23 - PAGE_SHIFT);
-
-	order = get_bitmask_order(limit) - 1 + PAGE_SHIFT;
-	limit = (1UL << order) / sizeof(struct hlist_head);
-	order = get_bitmask_order(min(limit, (unsigned long)UINT_MAX)) - 1;
-
 	for (i = 0; i < MAX_LINKS; i++) {
-		struct nl_portid_hash *hash = &nl_table[i].hash;
-
-		hash->table = nl_portid_hash_zalloc(1 * sizeof(*hash->table));
-		if (!hash->table) {
-			while (i-- > 0)
-				nl_portid_hash_free(nl_table[i].hash.table,
-						 1 * sizeof(*hash->table));
+		if (rhashtable_init(&nl_table[i].hash, &ht_params) < 0) {
+			while (--i > 0)
+				rhashtable_destroy(&nl_table[i].hash);
 			kfree(nl_table);
 			goto panic;
 		}
-		hash->max_shift = order;
-		hash->shift = 0;
-		hash->mask = 0;
-		hash->rehash_time = jiffies;
-
-		nl_table[i].compare = netlink_compare;
 	}
 
 	INIT_LIST_HEAD(&netlink_tap_all);
diff --git a/net/netlink/af_netlink.h b/net/netlink/af_netlink.h
index 0b59d44..60f631f 100644
--- a/net/netlink/af_netlink.h
+++ b/net/netlink/af_netlink.h
@@ -1,6 +1,7 @@
 #ifndef _AF_NETLINK_H
 #define _AF_NETLINK_H
 
+#include <linux/rhashtable.h>
 #include <net/sock.h>
 
 #define NLGRPSZ(x)	(ALIGN(x, sizeof(unsigned long) * 8) / 8)
@@ -47,6 +48,8 @@ struct netlink_sock {
 	struct netlink_ring	tx_ring;
 	atomic_t		mapped;
 #endif /* CONFIG_NETLINK_MMAP */
+
+	struct rhash_head	node;
 };
 
 static inline struct netlink_sock *nlk_sk(struct sock *sk)
@@ -54,21 +57,8 @@ static inline struct netlink_sock *nlk_sk(struct sock *sk)
 	return container_of(sk, struct netlink_sock, sk);
 }
 
-struct nl_portid_hash {
-	struct hlist_head	*table;
-	unsigned long		rehash_time;
-
-	unsigned int		mask;
-	unsigned int		shift;
-
-	unsigned int		entries;
-	unsigned int		max_shift;
-
-	u32			rnd;
-};
-
 struct netlink_table {
-	struct nl_portid_hash	hash;
+	struct rhashtable	hash;
 	struct hlist_head	mc_list;
 	struct listeners __rcu	*listeners;
 	unsigned int		flags;
diff --git a/net/netlink/diag.c b/net/netlink/diag.c
index 1af29624..7301850 100644
--- a/net/netlink/diag.c
+++ b/net/netlink/diag.c
@@ -4,6 +4,7 @@
 #include <linux/netlink.h>
 #include <linux/sock_diag.h>
 #include <linux/netlink_diag.h>
+#include <linux/rhashtable.h>
 
 #include "af_netlink.h"
 
@@ -101,16 +102,20 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
 				int protocol, int s_num)
 {
 	struct netlink_table *tbl = &nl_table[protocol];
-	struct nl_portid_hash *hash = &tbl->hash;
+	struct rhashtable *ht = &tbl->hash;
+	const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
 	struct net *net = sock_net(skb->sk);
 	struct netlink_diag_req *req;
+	struct netlink_sock *nlsk;
 	struct sock *sk;
 	int ret = 0, num = 0, i;
 
 	req = nlmsg_data(cb->nlh);
 
-	for (i = 0; i <= hash->mask; i++) {
-		sk_for_each(sk, &hash->table[i]) {
+	for (i = 0; i < htbl->size; i++) {
+		rht_for_each_entry(nlsk, htbl->buckets[i], ht, node) {
+			sk = (struct sock *)nlsk;
+
 			if (!net_eq(sock_net(sk), net))
 				continue;
 			if (num < s_num) {
-- 
1.9.3