On 11/11/2015 05:25 PM, Shuah Khan wrote: > On 11/11/2015 08:49 AM, Shuah Khan wrote: >> On 11/11/2015 08:36 AM, Mauro Carvalho Chehab wrote: >>> Em Wed, 11 Nov 2015 07:22:47 -0700 >>> Shuah Khan <shuahkh@xxxxxxxxxxxxxxx> escreveu: >>> >>>> On 11/11/2015 05:30 AM, Mauro Carvalho Chehab wrote: >>>>> Em Mon, 09 Nov 2015 08:55:06 -0700 >>>>> Shuah Khan <shuahkh@xxxxxxxxxxxxxxx> escreveu: >>>>> >>>>>> On 11/09/2015 08:51 AM, Shuah Khan wrote: >>>>>>> As I mentioned on the IRC, here is the log for the problems I am seeing. >>>>>>> I have to do eject HVR 950Q TV stick to see the problem. >>>>>>> >>>>>>> mc_next_gen.v8.4 branch with no changes. >>>>>>> >>>>>>> I can test and debug this week. >>>>>>> >>>>>>> thanks, >>>>>>> -- Shuah >>>>>>> >>>>>> >>>>>> Forgot to cc linux-media, just in case others are interested >>>>>> and have ideas on debugging. >>>>>> > > snip > >>>>> >>>>> Sorry, but I fail to see how this is related to the V4L2 subsystem. >>>>> >>>>> At least on my eyes, it seems that the bug is somewhere at the Radeon >>>>> driver. >>>>> >>>> >>>> Mauro, >>>> >>>> I think you didn't look down the dmesg far enough. The following is the >>>> problem I am talking about and you will see media_device_unregister() >>>> on the stack. This occurs as soon as the device is removed. >>> >>> Shuah, >>> >>> I saw that, but it is clear, from the above log, that the Radeon >>> driver is broken and it has some bad lock dependencies with the >>> driver_attach locks. Any other bad lock report related to the >>> Radeon driver or driver binding/unbiding code are very likely >>> related to the above bug. >>> >>> You should either fix the bad lock at the Radeon driver or not >>> load it at all, in order to be able to get any reliable results >>> about possible locking troubles with the MC drivers with the Kernel >>> lock tests. >>> >> >> Yeah Radeon driver bug could be making things worse. Did you see >> any problems with device removal during your testing? >> >> ok found the following commit that fixes the problem: >> 7231ed1a813e0a9d249bbbe58e66ca058aee83e1 >> >> This went into 4.2-rc4 or rc5. I will test applying just this >> one patch to mc_next_gen.v8.4 branch and see if device removal >> problem also goes away. >> > > Applied the acpi backlight fix and now kernel hangs solid when > device is removed. I managed to get stack trace enabling sysrq > and that showed media_device_unregister_entity() attempt to hold > spin_lock() -> raw_spin_lock() on the stack trace. It is same as > the one seen in the dmesg I sent. > > I think we have several calls to media_device_unregister_entity() > from various media core drivers (dvb, v4l2, bridge driver) during > device removal from their unregister paths. This adds lot of > contention on the mdev->lock. > > media_device_unregister() calls media_device_unregister_entity() > as well on all the mdev entities. > > I am not testing with my ALSA patches at the moment. When that > gets added, media_devnode_is_registered() check to ensure only > one of them (bridge driver or snd-usb-audio) runs > media_device_unregister() won't work as the MEDIA_FLAG_REGISTERED > flag gets cleared towards the end of media_device_unregister(). > media_device_unregister() needs to be safe to be run by these two > drivers and still do the work only once. media_device_unregister() > does a lot (removes interface links, interfaces, and then then > unregister entities before it removes the media device devnode > file and call media_devnode_unregister() to clear the > MEDIA_FLAG_REGISTERED bit. > > I see two problems to solve: > > - ensure media_device_unregister() is safe to be called by one > or more drivers during device removal (usb disconnect in this > case) > - Reduce contention on mdev->lock during device removal > > I have some ideas on how to do this. I can work on them and send > patches. Sounds like a plan? > Found a two line fix to the problem. Will send patch tomorrow. I was able to do device inserts and removals in a row with the change. It hangs every time device removed without the change. thanks, -- Shuah -- Shuah Khan Sr. Linux Kernel Developer Open Source Innovation Group Samsung Research America (Silicon Valley) shuahkh@xxxxxxxxxxxxxxx | (970) 217-8978 -- 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
