From: NeilBrown <neilb@suse.com>
To: Thomas Graf <tgraf@suug.ch>, Herbert Xu <herbert@gondor.apana.org.au>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 08/18] rhashtable: clean up dereference of ->future_tbl.
Date: Fri, 01 Jun 2018 14:44:09 +1000 [thread overview]
Message-ID: <152782824957.30340.14092720576731091742.stgit@noble> (raw)
In-Reply-To: <152782754287.30340.4395718227884933670.stgit@noble>
Using rht_dereference_bucket() to dereference
->future_tbl looks like a type error, and could be confusing.
Using rht_dereference_rcu() to test a pointer for NULL
adds an unnecessary barrier - rcu_access_pointer() is preferred
for NULL tests when no lock is held.
This uses 3 different ways to access ->future_tbl.
- if we know the mutex is held, use rht_dereference()
- if we don't hold the mutex, and are only testing for NULL,
use rcu_access_pointer()
- otherwise (using RCU protection for true dereference),
use rht_dereference_rcu().
Note that this includes a simplification of the call to
rhashtable_last_table() - we don't do an extra dereference
before the call any more.
Signed-off-by: NeilBrown <neilb@suse.com>
---
include/linux/rhashtable.h | 2 +-
lib/rhashtable.c | 9 ++++-----
2 files changed, 5 insertions(+), 6 deletions(-)
diff --git a/include/linux/rhashtable.h b/include/linux/rhashtable.h
index 49f80506d02e..10435a77b156 100644
--- a/include/linux/rhashtable.h
+++ b/include/linux/rhashtable.h
@@ -605,7 +605,7 @@ static inline void *__rhashtable_insert_fast(
lock = rht_bucket_lock(tbl, hash);
spin_lock_bh(lock);
- if (unlikely(rht_dereference_bucket(tbl->future_tbl, tbl, hash))) {
+ if (unlikely(rcu_access_pointer(tbl->future_tbl))) {
slow_path:
spin_unlock_bh(lock);
rcu_read_unlock();
diff --git a/lib/rhashtable.c b/lib/rhashtable.c
index b5d17bce19ff..1737fbd049da 100644
--- a/lib/rhashtable.c
+++ b/lib/rhashtable.c
@@ -226,8 +226,7 @@ static struct bucket_table *rhashtable_last_table(struct rhashtable *ht,
static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)
{
struct bucket_table *old_tbl = rht_dereference(ht->tbl, ht);
- struct bucket_table *new_tbl = rhashtable_last_table(ht,
- rht_dereference_rcu(old_tbl->future_tbl, ht));
+ struct bucket_table *new_tbl = rhashtable_last_table(ht, old_tbl);
struct rhash_head __rcu **pprev = rht_bucket_var(old_tbl, old_hash);
int err = -EAGAIN;
struct rhash_head *head, *next, *entry;
@@ -467,7 +466,7 @@ static int rhashtable_insert_rehash(struct rhashtable *ht,
fail:
/* Do not fail the insert if someone else did a rehash. */
- if (likely(rcu_dereference_raw(tbl->future_tbl)))
+ if (likely(rcu_access_pointer(tbl->future_tbl)))
return 0;
/* Schedule async rehash to retry allocation in process context. */
@@ -540,7 +539,7 @@ static struct bucket_table *rhashtable_insert_one(struct rhashtable *ht,
if (PTR_ERR(data) != -EAGAIN && PTR_ERR(data) != -ENOENT)
return ERR_CAST(data);
- new_tbl = rcu_dereference(tbl->future_tbl);
+ new_tbl = rht_dereference_rcu(tbl->future_tbl, ht);
if (new_tbl)
return new_tbl;
@@ -599,7 +598,7 @@ static void *rhashtable_try_insert(struct rhashtable *ht, const void *key,
break;
spin_unlock_bh(lock);
- tbl = rcu_dereference(tbl->future_tbl);
+ tbl = rht_dereference_rcu(tbl->future_tbl, ht);
}
data = rhashtable_lookup_one(ht, tbl, hash, key, obj);
next prev parent reply other threads:[~2018-06-01 4:46 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-01 4:44 [RFC PATCH 00/18] Assorted rhashtable improvements NeilBrown
2018-06-01 4:44 ` [PATCH 11/18] rhashtable: further improve stability of rhashtable_walk NeilBrown
2018-06-01 4:44 ` [PATCH 17/18] rhashtable: rename rht_for_each*continue as *from NeilBrown
2018-06-01 4:44 ` [PATCH 10/18] rhashtable: remove rhashtable_walk_peek() NeilBrown
2018-06-02 15:48 ` Herbert Xu
2018-06-04 0:30 ` NeilBrown
2018-06-04 1:18 ` Tom Herbert
2018-06-04 2:09 ` NeilBrown
2018-06-04 21:31 ` Tom Herbert
2018-06-04 22:13 ` Tom Herbert
2018-06-05 1:24 ` NeilBrown
2018-06-05 1:00 ` NeilBrown
[not found] ` <CALx6S36Ce-rXQMzmFYZVPGD10Bo6udvRAHiZ5gWwnzVwoTVv0w@mail.gmail.com>
2018-06-06 5:07 ` NeilBrown
2018-06-07 2:45 ` [PATCH - RFC] rhashtable: add rhashtable_walk_last_seen() NeilBrown
2018-06-07 2:46 ` [PATCH - RFC] rhashtable: implement rhashtable_walk_peek() using rhashtable_walk_last_seen() NeilBrown
[not found] ` <CALx6S35GgUOd0dPgv7P96wNNTv5pN7fij0pcAoccqcSWZhvY7Q@mail.gmail.com>
2018-06-12 2:48 ` [PATCH RFC v2] " NeilBrown
2018-06-14 17:41 ` Tom Herbert
2018-06-15 4:23 ` Herbert Xu
2018-06-15 5:31 ` NeilBrown
2018-06-01 4:44 ` [PATCH 18/18] rhashtable: add rhashtable_walk_delay_rehash() NeilBrown
2018-06-01 4:44 ` [PATCH 14/18] rhashtable: allow rht_bucket_var to return NULL NeilBrown
2018-06-01 4:44 ` [PATCH 15/18] rhashtable: use bit_spin_locks to protect hash bucket NeilBrown
2018-06-02 5:03 ` Herbert Xu
2018-06-02 9:53 ` Eric Dumazet
2018-06-04 0:25 ` NeilBrown
2018-06-04 2:52 ` [PATCH 15a/18] rhashtables: add lockdep tracking to bucket bit-spin-locks NeilBrown
2018-06-04 18:16 ` Simon Horman
2018-06-04 21:37 ` NeilBrown
2018-06-01 4:44 ` [PATCH 01/18] rhashtable: silence RCU warning in rhashtable_test NeilBrown
2018-06-01 4:44 ` [PATCH 07/18] rhashtable: use cmpxchg() to protect ->future_tbl NeilBrown
2018-06-01 16:44 ` Herbert Xu
2018-06-01 4:44 ` [PATCH 13/18] rhashtable: don't hold lock on first table throughout insertion NeilBrown
2018-06-01 4:44 ` [PATCH 16/18] rhashtable: allow percpu element counter NeilBrown
2018-06-01 4:44 ` [PATCH 03/18] rhashtable: remove nulls_base and related code NeilBrown
2018-06-07 2:49 ` NeilBrown
2018-06-13 6:25 ` Herbert Xu
2018-06-01 4:44 ` NeilBrown [this message]
2018-06-01 16:54 ` [PATCH 08/18] rhashtable: clean up dereference of ->future_tbl Herbert Xu
2018-06-01 4:44 ` [PATCH 06/18] rhashtable: simplify nested_table_alloc() and rht_bucket_nested_insert() NeilBrown
2018-06-01 16:28 ` Herbert Xu
2018-06-01 4:44 ` [PATCH 09/18] rhashtable: use cmpxchg() in nested_table_alloc() NeilBrown
2018-06-01 4:44 ` [PATCH 05/18] rhashtable: simplify INIT_RHT_NULLS_HEAD() NeilBrown
2018-06-01 16:24 ` Herbert Xu
2018-06-01 4:44 ` [PATCH 12/18] rhashtable: add rhashtable_walk_prev() NeilBrown
2018-06-01 4:44 ` [PATCH 02/18] rhashtable: split rhashtable.h NeilBrown
2018-06-01 10:48 ` Herbert Xu
2018-06-01 4:44 ` [PATCH 04/18] rhashtable: detect when object movement might have invalidated a lookup NeilBrown
2018-06-01 16:06 ` Herbert Xu
2018-06-04 3:38 ` NeilBrown
2018-07-06 7:08 ` [PATCH resend] " NeilBrown
2018-07-12 5:46 ` David Miller
2018-07-12 5:48 ` David Miller
2018-07-15 23:55 ` NeilBrown
2018-07-15 23:57 ` [PATCH - revised] " NeilBrown
2018-07-16 0:51 ` Herbert Xu
2018-07-16 1:23 ` NeilBrown
2018-07-16 2:16 ` Herbert Xu
2018-07-16 3:26 ` NeilBrown
2018-07-17 6:30 ` Herbert Xu
2018-07-20 6:24 ` NeilBrown
2018-07-18 20:14 ` David Miller
2018-07-20 6:30 ` NeilBrown
2018-07-20 6:43 ` David Miller
2018-07-20 7:09 ` NeilBrown
2018-07-23 1:56 ` [PATCH net-next] rhashtable: detect when object movement between tables " NeilBrown
2018-07-26 20:55 ` David Miller
2018-07-26 22:04 ` NeilBrown
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