On Tue, Feb 20, 2024 at 12:49 AM Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx> wrote: > > > Le 19/02/2024 à 14:10, syzbot a écrit : > > syzbot has bisected this issue to: > > > > commit c838530d230bc638d79b78737fc4488ffc28c1ee > > Author: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx> > > Date: Thu Nov 9 16:34:59 2023 +0000 > > > > media: media videobuf2: Be more flexible on the number of queue stored buffers > > > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=166dc872180000 > > start commit: b401b621758e Linux 6.8-rc5 > > git tree: upstream > > final oops: https://syzkaller.appspot.com/x/report.txt?x=156dc872180000 > > console output: https://syzkaller.appspot.com/x/log.txt?x=116dc872180000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=eff9f3183d0a20dd > > dashboard link: https://syzkaller.appspot.com/bug?extid=3b1d4b3d5f7a358bf9a9 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13ffaae8180000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13ef909c180000 > > > > Reported-by: syzbot+3b1d4b3d5f7a358bf9a9@xxxxxxxxxxxxxxxxxxxxxxxxx > > Fixes: c838530d230b ("media: media videobuf2: Be more flexible on the number of queue stored buffers") > > > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection > > Hans, > I think the issue occur because of this part of the commit: > @@ -1264,7 +1264,7 @@ void vb2_video_unregister_device(struct video_device *vdev) > */ > get_device(&vdev->dev); > video_unregister_device(vdev); > - if (vdev->queue && vdev->queue->owner) { > + if (vdev->queue) { > struct mutex *lock = vdev->queue->lock ? > vdev->queue->lock : vdev->lock; > > but I wonder if the correction shouldn't be to remove usbtv->vb2q_lock mutex in usbtv_video_free(). > > Any opinion ? That is probably what triggered the failure detected by syzbot, but I don't think we've ever had a guarantee that owner is NULL in that code. Looking at the uvc driver [1], it doesn't seem to need any special locking there (after all the vb2 code acquires them). (It also doesn't have the custom clean-up code that the usbtv driver has in usbtv_stop(), but that's another story). So maybe all we need to fix it is removing the mutex_lock/unlock() calls? [1] https://elixir.bootlin.com/linux/v6.8-rc4/source/drivers/media/usb/uvc/uvc_driver.c#L1906 Best, Tomasz
