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SubjectRe: Driver crash on kernel 2.6.32.7. Interaction between cx8800 (DVB-S) and USB HVR Hauppauge 950q
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On Thu, 2010-02-11 at 20:11 -0800, Greg KH wrote:
> On Wed, Feb 10, 2010 at 10:34:56AM -0500, Andy Walls wrote:
> > On Tue, 2010-02-09 at 22:12 -0500, Devin Heitmueller wrote:
> > > On Tue, Feb 9, 2010 at 10:05 PM, Richard Lemieux <rlemieu@cooptel.qc.ca> wrote:
> > > > Andy,
> > > >
> > > > This is a great answer! Thanks very much. When I get into this situation
> > > > again
> > > > I will know what to look for.
> > > >
> > > > A possible reason why I got into this problem in the first place is that I
> > > > tried
> > > > many combinations of parameters with mplayer and azap in order to learn how
> > > > to use the USB tuner in both the ATSC and the NTSC mode. I will look back
> > > > in the terminal history to see if I can find anything.
> > >
> > > I think the key to figuring out the bug at this point is you finding a
> > > sequence where you can reliably reproduce the oops. If we have that,
> > > then I can start giving you some code to try which we can see if it
> > > addresses the problem.
> > >
> > > For example, I would start by giving you a fix which results in us not
> > > calling the firmware release if the request_firmware() call failed,
> > > but it wouldn't be much help if you could not definitively tell me if
> > > the problem is fixed.
> >
> >
> > For the oops analysis here:
> >
> > http://article.gmane.org/gmane.linux.drivers.video-input-infrastructure/15954
> >
> >
> > I will also note that the file scope "fw_lock" mutex is rather
> > inconsistently used in
> > linux/drivers/base/fw_class.c:firmware_loading_store(). (I guess for
> > not wanting to consume the timeout interval with sleeping?)
> >
> > The mutex protects "case 1:", but all other cases appear to be only
> > protected by atomic status bit checks that can fall through to
> > fw_load_abort() which complete()'s the fw_priv->completion.
> >
> > Also not that in the _request_firmware() this sequence is the only place
> > a once good "fw_priv->fw" pointer is set to NULL:
> >
> > mutex_lock(&fw_lock);
> > if (!fw_priv->fw->size || test_bit(FW_STATUS_ABORT, &fw_priv->status)) {
> > retval = -ENOENT;
> > release_firmware(fw_priv->fw);
> > *firmware_p = NULL;
> > }
> > fw_priv->fw = NULL; <--------------- The only place it is set to NULL
> > mutex_unlock(&fw_lock);
> >
> >
> > So if the timeout timer fires at nearly the same time as udev coming in
> > and say "I'm done loading" without holding the mutex, one can run into
> > the Ooops. Not only that, I think the above code can leak memory under
> > some circumstances when the "if" clause is not satisfied.
> >
> > I think this really is a firmware_class.c issue. I think the "just
> > right" firmware loading timeouts and the particular computer system
> > responsiveness, make this Ooops possible. However, I'm amazed that a
> > single person has tripped it more than once.
> >
> > Revising the locking in linux/drivers/base/firmware_class.c should fix
> > the problem.
> >
> > I don't believe this comment in the code now:
> >
> > /* fw_lock could be moved to 'struct firmware_priv' but since it is just
> > * guarding for corner cases a global lock should be OK */
> > static DEFINE_MUTEX(fw_lock);
> >
> > struct firmware_priv {
> > char *fw_id;
> > ...
> >
> > And since "f_priv" is dynamically created and destroyed by
> > request_firmware() I see no harm in
> >
> > 1. moving the mutex into struct firmware_priv
> > 2. just always just grabbing an almost never contended mutex
> > 3. getting rid of the file scope fw_lock.
> >
> > except grabbing a mutex() while the timeout timer is running during
> > loading, means one *could* sleep for a while consuming the timeout
> > interval.
>
> That sounds reasonable to me, care to make up a patch for this?

Yes. But it will take me a while. I don't have a git tree, because I
don't have high bandwidth internet yet. (The cable company's been
delayed in laying cable to my home due to repeated snowstorms.)

I just didn't want the problem to fall through the cracks. I'll submit
something to bugzilla for now. If a user complains of this rare Ooops
when loading firmware, the current workaround is to lengthen the timeout
via sysfs.

Regards,
Andy

> thanks,
>
> greg k-h




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