3.16.83-rc2 review patch. If anyone has any objections, please let me know.
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From: Thomas Gleixner tglx@linutronix.de
commit 8d67743653dce5a0e7aa500fcccb237cde7ad88e upstream.
The recent futex inode life time fix changed the ordering of the futex key union struct members, but forgot to adjust the hash function accordingly,
As a result the hashing omits the leading 64bit and even hashes beyond the futex key causing a bad hash distribution which led to a ~100% performance regression.
Hand in the futex key pointer instead of a random struct member and make the size calculation based of the struct offset.
Fixes: 8019ad13ef7f ("futex: Fix inode life-time issue") Reported-by: Rong Chen rong.a.chen@intel.com Decoded-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Rong Chen rong.a.chen@intel.com Link: https://lkml.kernel.org/r/87h7yy90ve.fsf@nanos.tec.linutronix.de Signed-off-by: Ben Hutchings ben@decadent.org.uk Cc: Jann Horn jannh@google.com --- kernel/futex.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/kernel/futex.c +++ b/kernel/futex.c @@ -309,9 +309,9 @@ static inline int hb_waiters_pending(str */ static struct futex_hash_bucket *hash_futex(union futex_key *key) { - u32 hash = jhash2((u32*)&key->both.word, - (sizeof(key->both.word)+sizeof(key->both.ptr))/4, + u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4, key->both.offset); + return &futex_queues[hash & (futex_hashsize - 1)]; }