linux-kernel - Re: add_wait_queue() (unintentional?) behavior change in v4.13

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Message-ID: <20171206164344.iy57cvwgbsqhtwwz@gmail.com>
Date:   Wed, 6 Dec 2017 17:43:44 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Omar Sandoval <osandov@...ndov.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jens Axboe <axboe@...com>
Subject: Re: add_wait_queue() (unintentional?) behavior change in v4.13


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, Nov 29, 2017 at 4:58 PM, Omar Sandoval <osandov@...ndov.com> wrote:
> >
> > Note the change from __add_wait_queue() to
> > __add_wait_queue_entry_tail(). I'm assuming this was a typo since the
> > commit message doesn't mention any functional changes. This patch
> > restores the old behavior:
> >   [...]
> > I didn't go through and audit callers of add_wait_queue(), but from a
> > quick code read this makes it so that non-exclusive waiters will not be
> > woken up if they are behind enough exclusive waiters, and I bet that'll
> > cause some bugs.
> 
> This sounds right to me.
> 
> Ingo?

Yeah, it's indeed unintended and it's a bug - I have applied the fix and will get 
it to you ASAP.

Thanks,

	Ingo