| From bea736586da70f39a1e8a511ef2d6c25e956a9c3 Mon Sep 17 00:00:00 2001 |
| From: Thomas Gleixner <tglx@linutronix.de> |
| Date: Sun, 8 Mar 2020 19:07:17 +0100 |
| Subject: [PATCH] futex: Unbreak futex hashing |
| |
| 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: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/kernel/futex.c b/kernel/futex.c |
| index da5155cc51bd..5758f44c994a 100644 |
| --- a/kernel/futex.c |
| +++ b/kernel/futex.c |
| @@ -379,9 +379,9 @@ 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)]; |
| } |
| |
| -- |
| 2.7.4 |
| |
