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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 25963a6606d3180b308425a402075a4bb9d07e01)
Signed-off-by: Gajjala Chakradhar <gajjalac@motorola.com>
Change-Id: I25295391b13ba6e408afccfcd8d35724c94c39e0
Reviewed-on: https://gerrit.mot.com/2085476
SME-Granted: SME Approvals Granted
SLTApproved: Slta Waiver
Tested-by: Jira Key
Reviewed-by: Xiangpo Zhao <zhaoxp3@motorola.com>
Submit-Approved: Jira Key
(cherry picked from commit 1960ccb04d18ca01bac28207884984fd20bf65ea)

diff --git a/kernel/futex.c b/kernel/futex.c
index 1cd0b330b82ec36d87ec92a03927d469ff3e558f..4c172bba0b8a134f70d5186186bc1e7a22435259 100644 (file)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -392,9 +392,9 @@ 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)];
 }