Subject: Re: Possible locking issue in viotape.c
From: Daniel Walker <dwalker@mvista.com>
To: Kevin Winchester <kjwinchester@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, akpm@linux-foundation.org,
       linux-kernel@vger.kernel.org, linux@bohmer.net, jonathan@jonmasters.org,
       matthias.kaehlcke@gmail.com
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	 <47588610.5010804@gmail.com>
	 <1196989515.1568.131.camel@jnielson-xp.ddns.mvista.com>
	 <4758A216.3030401@gmail.com>
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Date: Thu, 06 Dec 2007 17:40:36 -0800
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On Thu, 2007-12-06 at 21:29 -0400, Kevin Winchester wrote:
> Daniel Walker wrote:
> > 
> > I've posted all the ones I've done so far ..
> > 
> > ftp://source.mvista.com/pub/dwalker/sem2mutex-2.6.24-rc4/
> > 
> > Feel free to review or test them.. I've found it pretty easy to simply
> > grep for certain class of semaphore usage, check if it's conforming to
> > the mutex requirements, then convert it or not.. Checking them is
> > getting to be a habit, so I don't think a list would help me.. However,
> > someone else might be able to use it..
> > 
> 
> Thanks, that helps me not duplicate anything.  One of the first ones I
> was looking at (before your post) was viotape.c, which is in your patch
> set.  However, looking at the uses of the semaphore, I see that on line
> 409-410 the following code:
> 
>         if (noblock)
>                 return count;
> 
> which seems to ignore the fact that the semaphore has been downed (not
> to mention the dma buffer and op struct allocations.  I think it should be:
> 
> 	if (noblock)
> 		ret = count;
> 		goto free_dma;
> 
> instead.  Do you want to make sure I'm right about that and fold it into
> your patch?  Or have you already submitted your patch (or should it be
> in a separate patch?  Alternatively, I can submit the patch if you don't
> want to bother with it.

viotape was one of the first I started converting, but later I noticed
the same thing you found above. I have it commented out of my series for
that reason ..

I think this noblock path is actually doing what the author intended..
There are a few stray up() calls related to event handling and ioctls ,
and I think those are used to release the semaphore..

Daniel


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