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From: David Howells <dhowells@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: dhowells@redhat.com, linux-cachefs@redhat.com,
	Trond Myklebust <trondmy@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Dominique Martinet <asmadeus@codewreck.org>,
	Jeff Layton <jlayton@kernel.org>,
	Matthew Wilcox <willy@infradead.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Omar Sandoval <osandov@osandov.com>,
	JeffleXu <jefflexu@linux.alibaba.com>,
	linux-afs@lists.infradead.org, "open list:NFS, SUNRPC,
	AND..." <linux-nfs@vger.kernel.org>,
	CIFS <linux-cifs@vger.kernel.org>,
	ceph-devel@vger.kernel.org, v9fs-developer@lists.sourceforge.net,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 07/67] fscache: Implement a hash function
Date: Fri, 10 Dec 2021 14:35:59 +0000	[thread overview]
Message-ID: <288130.1639146959@warthog.procyon.org.uk> (raw)
In-Reply-To: <CAHk-=whtkzB446+hX0zdLsdcUJsJ=8_-0S1mE_R+YurThfUbLA@mail.gmail.com>

Linus Torvalds <torvalds@linux-foundation.org> wrote:

> > What I'm trying to get at is that the hash needs to be consistent, no matter
> > the endianness of the cpu, for any particular input blob.
> 
> Yeah, if that's the case, then you should probably make that "unsigned
> int *data" argument probably just be "void *" and then:
> 
> >                 a = *data++;   <<<<<<<
> >                 HASH_MIX(x, y, a);
> >         }
> >         return fold_hash(x, y);
> > }
> >
> > The marked line should probably use something like le/be32_to_cpu().
> 
> Yes, it should be using a '__le32 *' inside that function and you
> should use l32_to_cpu(). Obviously, BE would work too, but cause
> unnecessary work on common hardware.

Okay, how about I make the attached change to make the hashing stable?  This
will make fscache_hash() take an opaque buffer and a length (the length must
be a multiple of four).

David
---
diff --git a/fs/fscache/cookie.c b/fs/fscache/cookie.c
index e287952292c5..65cf2ae22a70 100644
--- a/fs/fscache/cookie.c
+++ b/fs/fscache/cookie.c
@@ -269,22 +269,23 @@ EXPORT_SYMBOL(fscache_caching_failed);
 static int fscache_set_key(struct fscache_cookie *cookie,
 			   const void *index_key, size_t index_key_len)
 {
-	u32 *buf;
-	int bufs;
+	void *buf;
+	size_t buf_size;
 
-	bufs = DIV_ROUND_UP(index_key_len, sizeof(*buf));
+	buf_size = round_up(index_key_len, sizeof(__le32));
 
 	if (index_key_len > sizeof(cookie->inline_key)) {
-		buf = kcalloc(bufs, sizeof(*buf), GFP_KERNEL);
+		buf = kzalloc(buf_size, GFP_KERNEL);
 		if (!buf)
 			return -ENOMEM;
 		cookie->key = buf;
 	} else {
-		buf = (u32 *)cookie->inline_key;
+		buf = cookie->inline_key;
 	}
 
 	memcpy(buf, index_key, index_key_len);
-	cookie->key_hash = fscache_hash(cookie->volume->key_hash, buf, bufs);
+	cookie->key_hash = fscache_hash(cookie->volume->key_hash,
+					buf, buf_size);
 	return 0;
 }
 
diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index 87884f4b34fb..f121c21590dc 100644
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -86,7 +86,7 @@ static inline void fscache_end_operation(struct netfs_cache_resources *cres)
  */
 extern unsigned fscache_debug;
 
-extern unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n);
+extern unsigned int fscache_hash(unsigned int salt, const void *data, size_t len);
 
 /*
  * proc.c
diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index 01d57433702c..dad85fd84f6f 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -53,15 +53,16 @@ static inline unsigned int fold_hash(unsigned long x, unsigned long y)
 /*
  * Generate a hash.  This is derived from full_name_hash(), but we want to be
  * sure it is arch independent and that it doesn't change as bits of the
- * computed hash value might appear on disk.  The caller also guarantees that
- * the hashed data will be a series of aligned 32-bit words.
+ * computed hash value might appear on disk.  The caller must guarantee that
+ * the source data is a multiple of four bytes in size.
  */
-unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n)
+unsigned int fscache_hash(unsigned int salt, const void *data, size_t len)
 {
-	unsigned int a, x = 0, y = salt;
+	const __le32 *p = data;
+	unsigned int a, x = 0, y = salt, n = len / sizeof(__le32);
 
 	for (; n; n--) {
-		a = *data++;
+		a = le32_to_cpu(*p++);
 		HASH_MIX(x, y, a);
 	}
 	return fold_hash(x, y);
diff --git a/fs/fscache/volume.c b/fs/fscache/volume.c
index edd3c245010e..26a6b8f315e1 100644
--- a/fs/fscache/volume.c
+++ b/fs/fscache/volume.c
@@ -131,7 +131,7 @@ static long fscache_compare_volume(const struct fscache_volume *a,
 	if (a->key[0] != b->key[0])
 		return (long)a->key[0]   - (long)b->key[0];
 
-	klen = round_up(a->key[0] + 1, sizeof(unsigned int));
+	klen = round_up(a->key[0] + 1, sizeof(__le32));
 	return memcmp(a->key, b->key, klen);
 }
 
@@ -225,7 +225,7 @@ static struct fscache_volume *fscache_alloc_volume(const char *volume_key,
 	 * hashing easier.
 	 */
 	klen = strlen(volume_key);
-	hlen = round_up(1 + klen + 1, sizeof(unsigned int));
+	hlen = round_up(1 + klen + 1, sizeof(__le32));
 	key = kzalloc(hlen, GFP_KERNEL);
 	if (!key)
 		goto err_vol;
@@ -233,8 +233,7 @@ static struct fscache_volume *fscache_alloc_volume(const char *volume_key,
 	memcpy(key + 1, volume_key, klen);
 
 	volume->key = key;
-	volume->key_hash = fscache_hash(0, (unsigned int *)key,
-					hlen / sizeof(unsigned int));
+	volume->key_hash = fscache_hash(0, key, hlen);
 
 	volume->debug_id = atomic_inc_return(&fscache_volume_debug_id);
 	down_write(&fscache_addremove_sem);


  parent reply	other threads:[~2021-12-10 14:36 UTC|newest]

Thread overview: 88+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-09 16:53 [PATCH v2 00/67] fscache, cachefiles: Rewrite David Howells
2021-12-09 16:53 ` [PATCH v2 01/67] fscache, cachefiles: Disable configuration David Howells
2021-12-09 16:53 ` [PATCH v2 02/67] cachefiles: Delete the cachefiles driver pending rewrite David Howells
2021-12-09 16:54 ` [PATCH v2 03/67] fscache: Remove the contents of the fscache driver, " David Howells
2021-12-09 16:54 ` [PATCH v2 04/67] netfs: Display the netfs inode number in the netfs_read tracepoint David Howells
2021-12-09 16:54 ` [PATCH v2 05/67] netfs: Pass a flag to ->prepare_write() to say if there's no alloc'd space David Howells
2021-12-09 16:54 ` [PATCH v2 06/67] fscache: Introduce new driver David Howells
2021-12-09 16:54 ` [PATCH v2 07/67] fscache: Implement a hash function David Howells
2021-12-09 17:12   ` Linus Torvalds
2021-12-09 21:57   ` David Howells
2021-12-09 22:07     ` Linus Torvalds
2021-12-10 14:35     ` David Howells [this message]
2021-12-10 14:41     ` David Howells
2021-12-10 17:33       ` Linus Torvalds
2021-12-09 16:54 ` [PATCH v2 08/67] fscache: Implement cache registration David Howells
2021-12-14 18:36   ` Jeff Layton
2021-12-09 16:55 ` [PATCH v2 09/67] fscache: Implement volume registration David Howells
2021-12-09 17:32   ` Linus Torvalds
2021-12-14 18:52   ` Jeff Layton
2021-12-14 19:57   ` David Howells
2021-12-09 16:55 ` [PATCH v2 10/67] fscache: Implement cookie registration David Howells
2021-12-09 17:21   ` Linus Torvalds
2021-12-09 16:55 ` [PATCH v2 11/67] fscache: Implement cache-level access helpers David Howells
2021-12-09 16:55 ` [PATCH v2 12/67] fscache: Implement volume-level " David Howells
2021-12-09 16:55 ` [PATCH v2 13/67] fscache: Implement cookie-level " David Howells
2021-12-09 16:56 ` [PATCH v2 14/67] fscache: Implement functions add/remove a cache David Howells
2021-12-09 16:56 ` [PATCH v2 15/67] fscache: Provide and use cache methods to lookup/create/free a volume David Howells
2021-12-09 16:56 ` [PATCH v2 16/67] fscache: Add a function for a cache backend to note an I/O error David Howells
2021-12-09 16:57 ` [PATCH v2 17/67] fscache: Implement simple cookie state machine David Howells
2021-12-09 16:57 ` [PATCH v2 18/67] fscache: Implement cookie user counting and resource pinning David Howells
2021-12-09 16:58 ` [PATCH v2 19/67] fscache: Implement cookie invalidation David Howells
2021-12-09 16:58 ` [PATCH v2 20/67] fscache: Provide a means to begin an operation David Howells
2021-12-09 16:58 ` [PATCH v2 21/67] fscache: Count data storage objects in a cache David Howells
2021-12-09 16:58 ` [PATCH v2 22/67] fscache: Provide read/write stat counters for the cache David Howells
2021-12-09 16:58 ` [PATCH v2 23/67] fscache: Provide a function to let the netfs update its coherency data David Howells
2021-12-09 16:59 ` [PATCH v2 24/67] netfs: Pass more information on how to deal with a hole in the cache David Howells
2021-12-09 16:59 ` [PATCH v2 25/67] fscache: Implement raw I/O interface David Howells
2021-12-09 16:59 ` [PATCH v2 26/67] fscache: Implement higher-level write " David Howells
2021-12-09 16:59 ` [PATCH v2 27/67] vfs, fscache: Implement pinning of cache usage for writeback David Howells
2021-12-09 17:00 ` [PATCH v2 28/67] fscache: Provide a function to note the release of a page David Howells
2021-12-09 17:00 ` [PATCH v2 29/67] fscache: Provide a function to resize a cookie David Howells
2021-12-09 17:00 ` [PATCH v2 30/67] cachefiles: Introduce rewritten driver David Howells
2021-12-09 17:00 ` [PATCH v2 31/67] cachefiles: Define structs David Howells
2021-12-09 17:00 ` [PATCH v2 32/67] cachefiles: Add some error injection support David Howells
2021-12-09 17:01 ` [PATCH v2 33/67] cachefiles: Add a couple of tracepoints for logging errors David Howells
2021-12-09 17:01 ` [PATCH v2 34/67] cachefiles: Add cache error reporting macro David Howells
2021-12-09 17:01 ` [PATCH v2 35/67] cachefiles: Add security derivation David Howells
2021-12-09 17:01 ` [PATCH v2 36/67] cachefiles: Register a miscdev and parse commands over it David Howells
2021-12-09 17:01 ` [PATCH v2 37/67] cachefiles: Provide a function to check how much space there is David Howells
2021-12-09 17:01 ` [PATCH v2 38/67] vfs, cachefiles: Mark a backing file in use with an inode flag David Howells
2021-12-09 17:02 ` [PATCH v2 39/67] cachefiles: Implement a function to get/create a directory in the cache David Howells
2021-12-09 17:02 ` [PATCH v2 40/67] cachefiles: Implement cache registration and withdrawal David Howells
2021-12-09 17:02 ` [PATCH v2 41/67] cachefiles: Implement volume support David Howells
2021-12-09 17:03 ` [PATCH v2 42/67] cachefiles: Add tracepoints for calls to the VFS David Howells
2021-12-09 17:03 ` [PATCH v2 43/67] cachefiles: Implement object lifecycle funcs David Howells
2021-12-09 17:03 ` [PATCH v2 44/67] cachefiles: Implement key to filename encoding David Howells
2021-12-09 17:03 ` [PATCH v2 45/67] cachefiles: Implement metadata/coherency data storage in xattrs David Howells
2021-12-09 17:03 ` [PATCH v2 46/67] cachefiles: Mark a backing file in use with an inode flag David Howells
2021-12-09 17:04 ` [PATCH v2 47/67] cachefiles: Implement culling daemon commands David Howells
2021-12-09 17:04 ` [PATCH v2 48/67] cachefiles: Implement backing file wrangling David Howells
2021-12-09 17:05 ` [PATCH v2 49/67] cachefiles: Implement begin and end I/O operation David Howells
2021-12-09 17:05 ` [PATCH v2 50/67] cachefiles: Implement cookie resize for truncate David Howells
2021-12-09 17:05 ` [PATCH v2 51/67] cachefiles: Implement the I/O routines David Howells
2021-12-09 17:06 ` [PATCH v2 52/67] cachefiles: Allow cachefiles to actually function David Howells
2021-12-09 17:06 ` [PATCH v2 53/67] fscache, cachefiles: Display stats of no-space events David Howells
2021-12-09 17:06 ` [PATCH v2 54/67] fscache, cachefiles: Display stat of culling events David Howells
2021-12-09 17:07 ` [PATCH v2 55/67] afs: Handle len being extending over page end in write_begin/write_end David Howells
2021-12-09 17:08 ` [PATCH v2 56/67] afs: Fix afs_write_end() to handle len > page size David Howells
2021-12-09 17:08 ` [PATCH v2 57/67] afs: Convert afs to use the new fscache API David Howells
2021-12-09 17:08 ` [PATCH v2 58/67] afs: Copy local writes to the cache when writing to the server David Howells
2021-12-09 17:08 ` [PATCH v2 59/67] afs: Skip truncation on the server of data we haven't written yet David Howells
2021-12-09 17:09 ` [PATCH v2 60/67] 9p: Use fscache indexing rewrite and reenable caching David Howells
2021-12-09 17:09 ` [PATCH v2 61/67] 9p: Copy local writes to the cache when writing to the server David Howells
2021-12-09 17:09 ` [PATCH v2 62/67] nfs: Convert to new fscache volume/cookie API David Howells
2021-12-11 13:22   ` David Wysochanski
2021-12-11 13:37   ` David Howells
2021-12-09 17:10 ` [PATCH v2 63/67] nfs: Implement cache I/O by accessing the cache directly David Howells
2021-12-09 17:10 ` [PATCH v2 64/67] cifs: Support fscache indexing rewrite (untested) David Howells
2021-12-09 17:10 ` [PATCH v2 65/67] ceph: conversion to new fscache API David Howells
2021-12-09 17:10 ` [PATCH v2 66/67] ceph: add fscache writeback support David Howells
2021-12-09 17:11 ` [PATCH v2 67/67] fscache: Rewrite documentation David Howells
2021-12-10 18:38 ` [PATCH v2 00/67] fscache, cachefiles: Rewrite David Wysochanski
2021-12-11 13:44   ` David Wysochanski
2021-12-13 15:41   ` [PATCH] fscache: Need to go round again after processing LRU_DISCARDING state David Howells
2021-12-13 21:05     ` David Wysochanski
2021-12-13 16:22   ` David Howells
2021-12-13 20:03   ` David Howells
2021-12-13 22:39   ` David Howells

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