linux-kernel - Re: [PATCH] sched/wait: fix add_wait

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Date:   Wed, 6 Dec 2017 17:46:09 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Omar Sandoval <osandov@...ndov.com>, linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, kernel-team@...com
Subject: Re: [PATCH] sched/wait: fix add_wait_queue() behavior change


* Jens Axboe <axboe@...nel.dk> wrote:

> On 12/06/2017 12:15 AM, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@...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@...com>
> 
> Reviewed-by: Jens Axboe <axboe@...nel.dk>

Thanks!

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

Thanks,

	Ingo