On Tuesday, November 23, 2010 01:21:45 Laurent Pinchart wrote: > Hi Hans, > > On Tuesday 23 November 2010 01:14:28 Hans Verkuil wrote: > > On Monday, November 22, 2010 12:20:25 Hans Verkuil wrote: > > > On Monday, November 22, 2010 11:21:27 Laurent Pinchart wrote: > > > > Removing the mutex_lock/unlock around clear_bit allowed > > > > device_unregister() to race with v4l2_open(). The device can be > > > > unregistered between the video_devdata() and video_get() calls. > > > > > > > > Revert the patch to fix the problem. > > > > > > > > This reverts commit dd0daf2a6fb6bec436a3ef68bd585ea09a2a54b7. > > > > > > > > Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > > > > > > Acked-by: Hans Verkuil <hverkuil@xxxxxxxxx> > > > > Change of mind, I nack this. > > > > I realized that the mutex should be around device_unregister, not around > > the clear_bit. The mutex protects access to vdev->dev and not vdev->flags > > since that's atomic anyway. > > device_unregister() will end up calling v4l2_device_release(), which also > locks videodev_lock. That will result in a deadlock. True. (Note to myself: don't post past midnight...) But a mutex around clear_bit doesn't help either. Unless v4l2_open will test for this bit just before the video_get(). E.g. by replacing 'if (vdev == NULL)' with 'if (vdev == NULL || !video_is_registered(vdev))'. I think that will do the trick. Regards, Hans -- Hans Verkuil - video4linux developer - sponsored by Cisco -- 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
