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@xxxxxxxxxxxxx> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
