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| author | Thomas Gleixner <tglx@linutronix.de> | 2020-03-08 19:07:17 +0100 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2020-03-09 22:33:09 +0100 |
| commit | 8d67743653dce5a0e7aa500fcccb237cde7ad88e (patch) | |
| tree | 777ab98cc4f98ecf6d7ed407672811a91a57e9d5 /kernel/futex.c | |
| parent | 8019ad13ef7f64be44d4f892af9c840179009254 (diff) | |
| download | lwn-8d67743653dce5a0e7aa500fcccb237cde7ad88e.tar.gz lwn-8d67743653dce5a0e7aa500fcccb237cde7ad88e.zip | |
futex: Unbreak futex hashing
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
Diffstat (limited to 'kernel/futex.c')
| -rw-r--r-- | kernel/futex.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/futex.c b/kernel/futex.c index e14f7cd45dbd..82dfacb3250e 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -385,9 +385,9 @@ static inline int hb_waiters_pending(struct futex_hash_bucket *hb) */ 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)]; } |