linux-kernel - Re: Possible locking issue in viotape.c

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Message-Id: <1197138162.1568.172.camel@jnielson-xp.ddns.mvista.com>
Date:	Sat, 08 Dec 2007 10:22:42 -0800
From:	Daniel Walker <dwalker@...sta.com>
To:	Kevin Winchester <kjwinchester@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Possible locking issue in viotape.c

On Sat, 2007-12-08 at 14:17 -0400, Kevin Winchester wrote:
> Daniel Walker wrote:
> > 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
> > 
> > 
> 
> Yes, you are right, I hadn't finished looking at all of the up() calls
> when I came to my conclusion.  I will try to convert a few that are not
> on your list, but I would like to know how you are generating your
> patches into those files with the diffstat and recipient list.  Is that
> a feature of some git command?

Git may have a similar feature, but I'm using a tool call Quilt. It's
used for managing a list of patches, and it can automatically add a
diffstat to the patch header (part of the quilt refresh command). I also
use it for emailing a list of patches.

Daniel


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