Commit c6b9d9a3 authored Dec 05, 2017 by Omar Sandoval Committed by Ingo Molnar Dec 06, 2017

sched/wait: Fix add_wait_queue() behavioral change



The following cleanup commit:

  50816c48 ("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>

parent 328b4ed9

kernel/sched/wait.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -27,7 +27,7 @@ void add_wait_queue(struct wait_queue_head wq_head, struct wait_queue_entry wq

		wq_entry->flags &= ~WQ_FLAG_EXCLUSIVE;
		spin_lock_irqsave(&wq_head->lock, flags);
		__add_wait_queue_entry_tail(wq_head, wq_entry);
		__add_wait_queue(wq_head, wq_entry);
		spin_unlock_irqrestore(&wq_head->lock, flags);
		}
		EXPORT_SYMBOL(add_wait_queue);

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