Hi, On 04/11/13 14:54, 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/ We're discussing v4 actually ;) > 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/ [...] >>> -int vb2_fop_release(struct file *file) >>> +static int _vb2_fop_release(struct file *file, bool lock_is_held) >>> { >>> struct video_device *vdev = video_devdata(file); >>> + struct mutex *lock; >>> >>> if (file->private_data == vdev->queue->owner) { >>> + if (lock_is_held) >>> + lock = NULL; >>> + else >>> + lock = vdev->queue->lock ? >>> + vdev->queue->lock : vdev->lock; >>> + if (lock) >>> + mutex_lock(lock); >>> vb2_queue_release(vdev->queue); >>> vdev->queue->owner = NULL; >>> + if (lock) >>> + mutex_unlock(lock); >>> } >>> return v4l2_fh_release(file); >>> } >>> + >>> +int vb2_fop_release(struct file *file) >>> +{ >>> + return _vb2_fop_release(file, false); >>> +} >>> EXPORT_SYMBOL_GPL(vb2_fop_release); >>> >>> +int __vb2_fop_release(struct file *file) >>> +{ >>> + return _vb2_fop_release(file, true); >>> +} >>> +EXPORT_SYMBOL_GPL(__vb2_fop_release); >> >> Sorry for introducing yet another opinion, but I think this is very confusing. > > It is confusing the lock_held parameter or the __ naming for unlocked versions? > >> >> I would do this: >> >> static int __vb2_fop_release(struct file *file, struct mutex *lock) >> { >> struct video_device *vdev = video_devdata(file); >> >> if (file->private_data == vdev->queue->owner) { >> if (lock) >> mutex_lock(lock); >> vb2_queue_release(vdev->queue); >> vdev->queue->owner = NULL; >> if (lock) >> mutex_unlock(lock); >> } >> return v4l2_fh_release(file); >> } >> >> int vb2_fop_release(struct file *file) >> { >> struct video_device *vdev = video_devdata(file); >> struct mutex *lock = vdev->queue->lock ? >> vdev->queue->lock : vdev->lock; >> >> return __vb2_fop_release(file, lock); >> } >> EXPORT_SYMBOL_GPL(vb2_fop_release); >> >> int vb2_fop_release_unlock(struct file *file) >> { >> return __vb2_fop_release(file, NULL); >> } >> EXPORT_SYMBOL_GPL(vb2_fop_release_unlock); >> >> Optionally, __vb2_fop_release can be exported and then vb2_fop_release_unlock >> isn't necessary. >> > > i dont have any strong opinion in any direction. All I really care is > that the oops is fixed :). > > If your concern about the patch is the is_lock_held function, I can > make a patch with the params on your proposal and the __naming as > Sylvester suggested, so everyone is happy. > > Sylvester, Hanshat do you think? I like Hans' proposal, probably it's better to export __vb2_fop_release(), so it can be also used in cases like em28xx, to make things a bit more clear. But I'm fine with vb2_fop_release_unlock() as well, don't really have strong preference. It's up to you. -- Thanks, 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
