[syzbot] [usb?] [media?] possible deadlock in vb2_video_unregister_device

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ed5551279c91 Merge 6.8-rc3 into usb-next
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
console output: https://syzkaller.appspot.com/x/log.txt?x=16940d7be80000
kernel config: https://syzkaller.appspot.com/x/.config?x=28a3704ea90ef255
dashboard link: https://syzkaller.appspot.com/bug?extid=3b1d4b3d5f7a358bf9a9
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14450a38180000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1603629fe80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/10b543a7171a/disk-ed555127.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dc10f27643e8/vmlinux-ed555127.xz
kernel image: https://storage.googleapis.com/syzbot-assets/bb6389e754b9/bzImage-ed555127.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3b1d4b...@syzkaller.appspotmail.com

usb 1-1: SerialNumber: syz
usb 1-1: config 0 descriptor??
usbtv 1-1:0.0: Fushicai USBTV007 Audio-Video Grabber
usb 1-1: USB disconnect, device number 2
============================================
WARNING: possible recursive locking detected
6.8.0-rc3-syzkaller-00047-ged5551279c91 #0 Not tainted
--------------------------------------------
kworker/0:2/694 is trying to acquire lock:
ffff888109f20b70 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: vb2_video_unregister_device drivers/media/common/videobuf2/videobuf2-v4l2.c:1269 [inline]
ffff888109f20b70 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: vb2_video_unregister_device+0x12b/0x2d0 drivers/media/common/videobuf2/videobuf2-v4l2.c:1245

but task is already holding lock:
ffff888109f20b70 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: usbtv_video_free+0x28/0x70 drivers/media/usb/usbtv/usbtv-video.c:966

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&usbtv->vb2q_lock);
lock(&usbtv->vb2q_lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

7 locks held by kworker/0:2/694:
#0: ffff888106ad2138 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_one_work+0x789/0x15d0 kernel/workqueue.c:2608
#1: ffffc90001c0fd80 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_one_work+0x7eb/0x15d0 kernel/workqueue.c:2609
#2: ffff88810af2f190 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:990 [inline]
#2: ffff88810af2f190 (&dev->mutex){....}-{3:3}, at: hub_event+0x1be/0x4f40 drivers/usb/core/hub.c:5840
#3: ffff888107799190 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:990 [inline]
#3: ffff888107799190 (&dev->mutex){....}-{3:3}, at: usb_disconnect+0x10a/0x910 drivers/usb/core/hub.c:2287
#4: ffff88810779a160 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:990 [inline]
#4: ffff88810779a160 (&dev->mutex){....}-{3:3}, at: __device_driver_lock drivers/base/dd.c:1095 [inline]
#4: ffff88810779a160 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0xa4/0x610 drivers/base/dd.c:1292
#5: ffff888109f20b70 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: usbtv_video_free+0x28/0x70 drivers/media/usb/usbtv/usbtv-video.c:966
#6: ffff888109f20ae0 (&usbtv->v4l2_lock){+.+.}-{3:3}, at: usbtv_video_free+0x32/0x70 drivers/media/usb/usbtv/usbtv-video.c:967

stack backtrace:
CPU: 0 PID: 694 Comm: kworker/0:2 Not tainted 6.8.0-rc3-syzkaller-00047-ged5551279c91 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Workqueue: usb_hub_wq hub_event
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
check_deadlock kernel/locking/lockdep.c:3062 [inline]
validate_chain kernel/locking/lockdep.c:3856 [inline]
__lock_acquire+0x210a/0x3b30 kernel/locking/lockdep.c:5137
lock_acquire kernel/locking/lockdep.c:5754 [inline]
lock_acquire+0x1ae/0x520 kernel/locking/lockdep.c:5719
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x175/0x9d0 kernel/locking/mutex.c:752
vb2_video_unregister_device drivers/media/common/videobuf2/videobuf2-v4l2.c:1269 [inline]
vb2_video_unregister_device+0x12b/0x2d0 drivers/media/common/videobuf2/videobuf2-v4l2.c:1245
usbtv_video_free+0x4a/0x70 drivers/media/usb/usbtv/usbtv-video.c:970
usbtv_disconnect+0x5c/0xd0 drivers/media/usb/usbtv/usbtv-core.c:138
usb_unbind_interface+0x1e5/0x960 drivers/usb/core/driver.c:461
device_remove drivers/base/dd.c:569 [inline]
device_remove+0x11f/0x170 drivers/base/dd.c:561
__device_release_driver drivers/base/dd.c:1272 [inline]
device_release_driver_internal+0x44a/0x610 drivers/base/dd.c:1295
bus_remove_device+0x22c/0x420 drivers/base/bus.c:574
device_del+0x39a/0xa50 drivers/base/core.c:3814
usb_disable_device+0x36c/0x7f0 drivers/usb/core/message.c:1416
usb_disconnect+0x2e1/0x910 drivers/usb/core/hub.c:2296
hub_port_connect drivers/usb/core/hub.c:5352 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5652 [inline]
port_event drivers/usb/core/hub.c:5812 [inline]
hub_event+0x1be0/0x4f40 drivers/usb/core/hub.c:5894
process_one_work+0x886/0x15d0 kernel/workqueue.c:2633
process_scheduled_works kernel/workqueue.c:2706 [inline]
worker_thread+0x8b9/0x1290 kernel/workqueue.c:2787
kthread+0x2c6/0x3a0 kernel/kthread.c:388
ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:242
</TASK>


---
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[Hillf Danton]

On Wed, 07 Feb 2024 00:44:22 -0800

> HEAD commit: ed5551279c91 Merge 6.8-rc3 into usb-next
> git tree: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing

> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1603629fe80000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing

--- x/drivers/media/usb/usbtv/usbtv-video.c
+++ y/drivers/media/usb/usbtv/usbtv-video.c
@@ -963,11 +963,11 @@ ctrl_fail:

void usbtv_video_free(struct usbtv *usbtv)
{
+ usbtv_stop(usbtv);
+ vb2_video_unregister_device(&usbtv->vdev);
mutex_lock(&usbtv->vb2q_lock);
mutex_lock(&usbtv->v4l2_lock);

- usbtv_stop(usbtv);
- vb2_video_unregister_device(&usbtv->vdev);
v4l2_device_disconnect(&usbtv->v4l2_dev);

mutex_unlock(&usbtv->v4l2_lock);
--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+3b1d4b...@syzkaller.appspotmail.com

Tested on:

commit: ed555127 Merge 6.8-rc3 into usb-next

git tree: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing

console output: https://syzkaller.appspot.com/x/log.txt?x=13796624180000

kernel config: https://syzkaller.appspot.com/x/.config?x=28a3704ea90ef255
dashboard link: https://syzkaller.appspot.com/bug?extid=3b1d4b3d5f7a358bf9a9
compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=15126718180000

Note: testing is done by a robot and is best-effort only.

[Tomasz Figa]

Looking at usbtv_video_free [1], it calls
vb2_video_unregister_device() with the queue mutex locked, which is
just wrong. I wonder how (and if) it even worked before. Laurent,
Hans, Mauro, any idea who is maintaining this driver? I don't see a
matching entry in the MAINTAINERS file.

[1] https://elixir.bootlin.com/linux/v6.8-rc4/source/drivers/media/usb/usbtv/usbtv-video.c#L964

Best regards,
Tomasz

[syzbot]

syzbot has bisected this issue to:

commit c838530d230bc638d79b78737fc4488ffc28c1ee
Author: Benjamin Gaignard <benjamin...@collabora.com>
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+3b1d4b...@syzkaller.appspotmail.com
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

[Benjamin Gaignard]

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 ?

Regards,
Benjamin

>

[Tomasz Figa]

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