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sched/wait: Fix add_wait_queue() behavioral change
authorOmar Sandoval <osandov@fb.com>
Wed, 6 Dec 2017 07:15:31 +0000 (23:15 -0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Fri, 16 Feb 2018 19:22:43 +0000 (20:22 +0100)
commite94a7de2a3d2da42f0d124c7501195f1cdffa232
tree91b4cce9d6c18aa1b83cab8e90fd7f3efa5d9cb7
parent69373cdc4ae4eacac2eb19da03eb0ad2bb0eda7f
sched/wait: Fix add_wait_queue() behavioral change

commit c6b9d9a33029014446bd9ed84c1688f6d3d4eab9 upstream.

The following cleanup commit:

  50816c48997a ("sched/wait: Standardize internal naming of wait-queue entries")

... unintentionally changed the behavior of add_wait_queue() from
inserting the wait entry at the head of the wait queue to the tail
of the wait queue.

Beyond a negative performance impact this change in behavior
theoretically also breaks wait queues which mix exclusive and
non-exclusive waiters, as non-exclusive waiters will not be
woken up if they are queued behind enough exclusive waiters.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: kernel-team@fb.com
Fixes: ("sched/wait: Standardize internal naming of wait-queue entries")
Link: http://lkml.kernel.org/r/a16c8ccffd39bd08fdaa45a5192294c784b803a7.1512544324.git.osandov@fb.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
kernel/sched/wait.c