Hello Hans and Sywester I have just posted a new patch. I think it fits the suggestions from both of you, please take a look to it and please post any comment. I will also send a patch about the em28xx, to swap the lock order. Thanks for your comments On Mon, Nov 4, 2013 at 4:19 PM, Hans Verkuil <hverkuil@xxxxxxxxx> wrote: > 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 >> > -- Ricardo Ribalda -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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