linux-kernel - Re: [PATCH] wait: fix false timeouts when using wait_event

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Message-ID: <1367524609.19739.8.camel@ideak-mobl>
Date:	Thu, 02 May 2013 22:56:49 +0300
From:	Imre Deak <imre.deak@...el.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	David Howells <dhowells@...hat.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dave Jones <davej@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] wait: fix false timeouts when using wait_event_timeout()

On Thu, 2013-05-02 at 14:35 +0200, Jens Axboe wrote:
> On Thu, May 02 2013, David Howells wrote:
> > Imre Deak <imre.deak@...el.com> wrote:
> > 
> > > Many callers of the wait_event_timeout() and
> > > wait_event_interruptible_timeout() expect that the return value will be
> > > positive if the specified condition becomes true before the timeout
> > > elapses. However, at the moment this isn't guaranteed. If the wake-up
> > > handler is delayed enough, the time remaining until timeout will be
> > > calculated as 0 - and passed back as a return value - even if the
> > > condition became true before the timeout has passed.
> > > 
> > > Fix this by returning at least 1 if the condition becomes true. This
> > > semantic is in line with what wait_for_condition_timeout() does; see
> > > commit bb10ed09 - "sched: fix wait_for_completion_timeout() spurious
> > > failure under heavy load".
> > > 
> > > Signed-off-by: Imre Deak <imre.deak@...el.com>
> > 
> > Acked-by: David Howells <dhowells@...hat.com>
> 
> You can add mine, too:
> 
> Acked-by: Jens Axboe <axboe@...nel.dk>

Ok, I think we agree that the +1 thing in schedule_timeout() discussed
in this thread should be handled separately, so if there is no other
objection I'd be happy if this patch was merged through someone's tree
as-is.

--Imre


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