linux-kernel - Re: [PATCH] sound: Fix race condition in the pcm

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Message-ID: <20110906200736.785edef3@infradead.org>
Date:	Tue, 6 Sep 2011 20:07:36 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	perex@...ex.cz, tiwai@...e.de
Subject: Re: [PATCH] sound: Fix race condition in the pcm_lib "wait for
 space loop

On Tue, 6 Sep 2011 15:59:54 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> > --- a/sound/core/pcm_lib.c
> > +++ b/sound/core/pcm_lib.c
> > @@ -1761,6 +1761,10 @@ static int wait_for_avail(struct
> > snd_pcm_substream *substream, snd_pcm_uframes_t avail = 0;
> >  	long wait_time, tout;
> >  
> > +	init_waitqueue_entry(&wait, current);
> > +	add_wait_queue(&runtime->tsleep, &wait);
> > +	set_current_state(TASK_INTERRUPTIBLE);
> 
> Well, this isn't very good either.  if a wakeup gets delivered to
> runtime->tsleep before the set_current_state(), this process will go
> ahead and incorrectly set itself into TASK_INTERRUPTIBLE state.

... and then check the condition for exit, and then set it to
TASK_RUNABLE a the end...

> 
> That looks like it will be dont-care/cant-happen in this case, but
> it's setting a bad example.

agreed that your ordering is more clean/better.....



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
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