From a5c21dcefa1c3d759457a604b3cfc4af29c8713f Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 12 Dec 2013 17:40:21 +0000 Subject: dcache: allow word-at-a-time name hashing with big-endian CPUs When explicitly hashing the end of a string with the word-at-a-time interface, we have to be careful which end of the word we pick up. On big-endian CPUs, the upper-bits will contain the data we're after, so ensure we generate our masks accordingly (and avoid hashing whatever random junk may have been sitting after the string). This patch adds a new dcache helper, bytemask_from_count, which creates a mask appropriate for the CPU endianness. Cc: Al Viro Signed-off-by: Will Deacon Signed-off-by: Linus Torvalds --- fs/dcache.c | 2 +- fs/namei.c | 7 +------ 2 files changed, 2 insertions(+), 7 deletions(-) (limited to 'fs') diff --git a/fs/dcache.c b/fs/dcache.c index 4bdb300b16e..6055d61811d 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -192,7 +192,7 @@ static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char if (!tcount) return 0; } - mask = ~(~0ul << tcount*8); + mask = bytemask_from_count(tcount); return unlikely(!!((a ^ b) & mask)); } diff --git a/fs/namei.c b/fs/namei.c index c53d3a9547f..3531deebad3 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1598,11 +1598,6 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd) * do a "get_unaligned()" if this helps and is sufficiently * fast. * - * - Little-endian machines (so that we can generate the mask - * of low bytes efficiently). Again, we *could* do a byte - * swapping load on big-endian architectures if that is not - * expensive enough to make the optimization worthless. - * * - non-CONFIG_DEBUG_PAGEALLOC configurations (so that we * do not trap on the (extremely unlikely) case of a page * crossing operation. @@ -1646,7 +1641,7 @@ unsigned int full_name_hash(const unsigned char *name, unsigned int len) if (!len) goto done; } - mask = ~(~0ul << len*8); + mask = bytemask_from_count(len); hash += mask & a; done: return fold_hash(hash); -- cgit v1.2.3