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Date: Wed, 6 Dec 2017 17:46:09 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: Omar Sandoval <osandov@osandov.com>, linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        kernel-team@fb.com
Subject: Re: [PATCH] sched/wait: fix add_wait_queue() behavior change
Message-ID: <20171206164609.64fmke7mjk2y3of3@gmail.com>
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* Jens Axboe <axboe@kernel.dk> wrote:

> On 12/06/2017 12:15 AM, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@fb.com>
> > 
> > Commit 50816c48997a ("sched/wait: Standardize internal naming of
> > wait-queue entries") 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. That commit was a cleanup and didn't mention any
> > functional changes so it was likely unintentional. This change in
> > behavior theoretically 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.
> 
> Ingo? You've been silent on this issue, which is somewhat odd since
> your cosmetic renaming patch introduced this behavioral change.
> 
> Omar, should probably turn that into a proper Fixes: line as
> well.
> 
> > Signed-off-by: Omar Sandoval <osandov@fb.com>
> 
> Reviewed-by: Jens Axboe <axboe@kernel.dk>

Thanks!

I've applied the fix and will send it to Linus later today.

Thanks,

	Ingo