Re: [syzbot] [media?] [usb?] INFO: task hung in vb2_video_unregister_device

syzbot
2024-02-29T07:51:03Z

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in vb2_video_unregister_device

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-rc6-syzkaller-g805d849d7c3c-dirty #0 Not tainted
--------------------------------------------
kworker/0:4/6186 is trying to acquire lock:
ffff0000cd544b90 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: vb2_video_unregister_device+0xe8/0x1ac drivers/media/common/videobuf2/videobuf2-v4l2.c:1268

but task is already holding lock:
ffff0000cd544b90 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: usbtv_video_free+0x2c/0x84 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/0:4/6186:
#0: ffff0000c252f138 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_one_work+0x560/0x1204 kernel/workqueue.c:2606
#1: ffff800097b77c20 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_one_work+0x5a0/0x1204 kernel/workqueue.c:2608
#2: ffff0000ccf38190 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:990 [inline]
#2: ffff0000ccf38190 (&dev->mutex){....}-{3:3}, at: hub_event+0x1b4/0x435c drivers/usb/core/hub.c:5811
#3: ffff0000c73fb190 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:990 [inline]
#3: ffff0000c73fb190 (&dev->mutex){....}-{3:3}, at: usb_disconnect+0xec/0x808 drivers/usb/core/hub.c:2258
#4: ffff0000d811b160 (&dev->mutex){....}-{3:3}, at: device_lock include/linux/device.h:990 [inline]
#4: ffff0000d811b160 (&dev->mutex){....}-{3:3}, at: __device_driver_lock drivers/base/dd.c:1095 [inline]
#4: ffff0000d811b160 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0xbc/0x6a0 drivers/base/dd.c:1292
#5: ffff0000cd544b90 (&usbtv->vb2q_lock){+.+.}-{3:3}, at: usbtv_video_free+0x2c/0x84 drivers/media/usb/usbtv/usbtv-video.c:966
#6: ffff0000cd544b00 (&usbtv->v4l2_lock){+.+.}-{3:3}, at: usbtv_video_free+0x3c/0x84 drivers/media/usb/usbtv/usbtv-video.c:967

stack backtrace:
CPU: 0 PID: 6186 Comm: kworker/0:4 Not tainted 6.8.0-rc6-syzkaller-g805d849d7c3c-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
Workqueue: usb_hub_wq hub_event
Call trace:
dump_backtrace+0x1b8/0x1e4 arch/arm64/kernel/stacktrace.c:291
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:298
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd0/0x124 lib/dump_stack.c:106
dump_stack+0x1c/0x28 lib/dump_stack.c:113
print_deadlock_bug+0x4e4/0x660 kernel/locking/lockdep.c:3012
check_deadlock kernel/locking/lockdep.c:3062 [inline]
validate_chain kernel/locking/lockdep.c:3856 [inline]
__lock_acquire+0x5fe4/0x763c kernel/locking/lockdep.c:5137
lock_acquire+0x23c/0x71c kernel/locking/lockdep.c:5754
__mutex_lock_common+0x190/0x21a0 kernel/locking/mutex.c:608
__mutex_lock kernel/locking/mutex.c:752 [inline]
mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:804
vb2_video_unregister_device+0xe8/0x1ac drivers/media/common/videobuf2/videobuf2-v4l2.c:1268
usbtv_video_free+0x4c/0x84 drivers/media/usb/usbtv/usbtv-video.c:970
usbtv_disconnect+0x6c/0xc4 drivers/media/usb/usbtv/usbtv-core.c:138
usb_unbind_interface+0x1a4/0x758 drivers/usb/core/driver.c:461
device_remove drivers/base/dd.c:569 [inline]
__device_release_driver drivers/base/dd.c:1272 [inline]
device_release_driver_internal+0x440/0x6a0 drivers/base/dd.c:1295
device_release_driver+0x28/0x38 drivers/base/dd.c:1318
bus_remove_device+0x314/0x3b4 drivers/base/bus.c:574
device_del+0x480/0x87c drivers/base/core.c:3828
usb_disable_device+0x354/0x760 drivers/usb/core/message.c:1416
usb_disconnect+0x290/0x808 drivers/usb/core/hub.c:2267
hub_port_connect drivers/usb/core/hub.c:5323 [inline]
hub_port_connect_change drivers/usb/core/hub.c:5623 [inline]
port_event drivers/usb/core/hub.c:5783 [inline]
hub_event+0x18ec/0x435c drivers/usb/core/hub.c:5865
process_one_work+0x694/0x1204 kernel/workqueue.c:2633
process_scheduled_works kernel/workqueue.c:2706 [inline]
worker_thread+0x970/0xef4 kernel/workqueue.c:2787
kthread+0x288/0x310 kernel/kthread.c:388
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860

Tested on:

commit: 805d849d Merge tag 'acpi-6.8-rc7' of git://git.kernel...
git tree: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=12b53522180000
kernel config: https://syzkaller.appspot.com/x/.config?x=e412105d06db24c2
dashboard link: https://syzkaller.appspot.com/bug?extid=2622b51b35f91a00ea18
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
patch: https://syzkaller.appspot.com/x/patch.diff?x=17181132180000