[alsa-devel] [patch 1/2] OSS: soundcard: locking bug in sound_ioctl()

[Arnd Bergmann]

On Sunday 10 October 2010 20:39:34 Arnd Bergmann wrote:
> On Sunday 10 October 2010 19:33:52 Dan Carpenter wrote:
> > We shouldn't return directly here because we're still holding the
> > &soundcard_mutex.
> > 
> > This bug goes all the way back to the start of git.  It's strange that
> > no one has complained about it as a runtime bug.
> > 
> > CC: stable at kernel.org
> > Signed-off-by: Dan Carpenter <error27 at gmail.com>
> 
> It was only recently converted to a mutex from the BKL, which is much
> more friendly to misusage because it is automatically released when
> the kernel sleeps or when the program exits.
> 
> The behavior was already broken with the BKL but the problem was far
> less visible. I fear we might be seeing more of these as fallout from
> the BKL removal. Sparse should be able to detect most of these cases
> though, so maybe we can look more carefully for them.
 
Hmm, actually sparse does *not* warn about sound_ioctl returning in
different lock contexts. Sparse developers: is there a known limitation
in sparse for this? I expected to see context warnings because
sound_ioctl normally releases soundcard_mutex (previously lock_kernel)
in some cases returns while holding the lock.

	Arnd