Subject: Re: [PATCH] sched/wait: fix add_wait_queue() behavior change
To: 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>
Cc: kernel-team@fb.com
References: <CA+55aFwhq-ZyDW2SYhYDg1ytKybwHywiH9jW3UmMu=YAgk694Q@mail.gmail.com>
 <a16c8ccffd39bd08fdaa45a5192294c784b803a7.1512544324.git.osandov@fb.com>
From: Jens Axboe <axboe@kernel.dk>
Message-ID: <5589355c-7b6a-91ff-3916-e60e9ac64d9d@kernel.dk>
Date: Wed, 6 Dec 2017 09:11:03 -0700
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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>

-- 
Jens Axboe