On 11/04/2013 03:24 PM, Sylwester Nawrocki wrote: > On 04/11/13 15:12, Hans Verkuil wrote: >> On 11/04/2013 02:54 PM, Ricardo Ribalda Delgado wrote: >>>> Hello Hans >>>> >>>> Thanks for your comments. >>>> >>>> Please take a look to v4 of this patch >>>> https://patchwork.linuxtv.org/patch/20529/ >>>> >>>> On Mon, Nov 4, 2013 at 1:37 PM, Hans Verkuil <hverkuil@xxxxxxxxx> wrote: >>>>>> On 11/02/2013 10:53 AM, Ricardo Ribalda Delgado wrote: >>>>>>>> From: Ricardo Ribalda <ricardo.ribalda@xxxxxxxxx> >>>>>>>> >>>>>>>> vb2_fop_relase does not held the lock although it is modifying the >>>>>>>> queue->owner field. >>>>>>>> >>>>>>>> This could lead to race conditions on the vb2_perform_io function >>>>>>>> when multiple applications are accessing the video device via >>>>>>>> read/write API: >>>>>> >>>>>> It's also called directly by drivers/media/usb/em28xx/em28xx-video.c! >>>>>> >>>> >>>> em28xx-video does not hold the lock, therefore it can call the normal >>>> function. On v2 we made a internal function that should be called if >>>> the funciton is called directly by the driver. Please take a look to >>>> the old comments. https://patchwork.linuxtv.org/patch/20460/ >> >> static int em28xx_v4l2_close(struct file *filp) >> { >> struct em28xx_fh *fh = filp->private_data; >> struct em28xx *dev = fh->dev; >> int errCode; >> >> em28xx_videodbg("users=%d\n", dev->users); >> >> mutex_lock(&dev->lock); >> vb2_fop_release(filp); >> ... >> >> vb2_fop_release(filp) will, with your patch, also try to get dev->lock. >> >> Sylwester's comment re em28xx is incorrect. > > dev->lock is not used as the video queue lock: > > $ git grep "lock =" drivers/media/usb/em28xx/ > ... > drivers/media/usb/em28xx/em28xx-video.c: dev->vdev->queue->lock = &dev->vb_queue_lock; > drivers/media/usb/em28xx/em28xx-video.c: dev->vbi_dev->queue->lock = &dev->vb_vbi_queue_lock; > > There is a separate mutex for the video queue which needs to be acquired > independently. Darn, I missed that one. I was looking for it in em28xx_vdev_init(), which is where I expected the queue->lock to be set, if there was any. That said, wouldn't it be a good idea to swap the order: vb2_fop_release(filp); mutex_lock(&dev->lock); I don't believe there is a good reason for nesting mutexes here. Regards, Hans > > -- > Regards, > Sylwester > -- > 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 > -- 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
