linux-kernel - Re: mcdx -- do_request(): non-read command to cd!!

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Date:	Wed, 4 Apr 2007 09:30:43 +0300
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Rene Herman" <rene.herman@...il.com>
Cc:	linux-kernel@...r.kernel.org, "Jens Axboe" <jens.axboe@...cle.com>
Subject: Re: mcdx -- do_request(): non-read command to cd!!

On 4/4/07, Rene Herman <rene.herman@...il.com> wrote:
> Taking forever to reproduce in as far as getting the oops. The thing is
> now just locking hard each time. Will keep on trying...

Can you get anything out with sysrq-t? The original oops would be
enough to conclude it's a double-free if it weren't for this:

    if (stuffp->toc) {
           kfree(stuffp->toc);
           stuffp->toc = NULL;
    }

While the code is obviously unsafe, we would have to be interrupted
between the read and the assignment, but you don't even have preempt
enabled! So I don't quite yet see where the concurrency is coming
from.

What you can do here is protect the above sequence with a spinlock,
for example, which might paper-over the double-free enough to get you
running again...

                                       Pekka
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