Re: possible deadlock in v4l2_release

From: syzbot
Date: Sat Nov 17 2018 - 03:24:51 EST

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In reply to: syzbot: "possible deadlock in v4l2_release"
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syzbot has found a reproducer for the following crash on:

HEAD commit: 1ce80e0fe98e Merge tag 'fsnotify_for_v4.20-rc3' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=132ee77b400000
kernel config: https://syzkaller.appspot.com/x/.config?x=d86f24333880b605
dashboard link: https://syzkaller.appspot.com/bug?extid=ea05c832a73d0615bf33
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10b8e6a3400000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=14e73e2b400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+ea05c832a73d0615bf33@xxxxxxxxxxxxxxxxxxxxxxxxx

sshd (5890) used greatest stack depth: 15744 bytes left

======================================================
WARNING: possible circular locking dependency detected
4.20.0-rc2+ #338 Not tainted
------------------------------------------------------
kworker/0:2/3421 is trying to acquire lock:
00000000c364a3bd (&mdev->req_queue_mutex){+.+.}, at: v4l2_release+0x1d7/0x3a0 drivers/media/v4l2-core/v4l2-dev.c:455

but task is already holding lock:
000000009258f90c ((delayed_fput_work).work){+.+.}, at: process_one_work+0xb9a/0x1c40 kernel/workqueue.c:2128

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 ((delayed_fput_work).work){+.+.}:
process_one_work+0xc0a/0x1c40 kernel/workqueue.c:2129
worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
kthread+0x35a/0x440 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

-> #2 ((wq_completion)"events"){+.+.}:
flush_workqueue+0x30a/0x1e10 kernel/workqueue.c:2655
flush_scheduled_work include/linux/workqueue.h:599 [inline]
vim2m_stop_streaming+0x7c/0x2c0 drivers/media/platform/vim2m.c:811
__vb2_queue_cancel+0x171/0xd20 drivers/media/common/videobuf2/videobuf2-core.c:1823
vb2_core_queue_release+0x26/0x80 drivers/media/common/videobuf2/videobuf2-core.c:2229
vb2_queue_release+0x15/0x20 drivers/media/common/videobuf2/videobuf2-v4l2.c:837
v4l2_m2m_ctx_release+0x1e/0x35 drivers/media/v4l2-core/v4l2-mem2mem.c:930
vim2m_release+0xe6/0x150 drivers/media/platform/vim2m.c:977
v4l2_release+0x224/0x3a0 drivers/media/v4l2-core/v4l2-dev.c:456
__fput+0x385/0xa30 fs/file_table.c:278
____fput+0x15/0x20 fs/file_table.c:309
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&dev->dev_mutex){+.+.}:
__mutex_lock_common kernel/locking/mutex.c:925 [inline]
__mutex_lock+0x166/0x16f0 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
vim2m_release+0xbc/0x150 drivers/media/platform/vim2m.c:976
v4l2_release+0x224/0x3a0 drivers/media/v4l2-core/v4l2-dev.c:456
__fput+0x385/0xa30 fs/file_table.c:278
____fput+0x15/0x20 fs/file_table.c:309
task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:188 [inline]
exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&mdev->req_queue_mutex){+.+.}:
lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844
__mutex_lock_common kernel/locking/mutex.c:925 [inline]
__mutex_lock+0x166/0x16f0 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
v4l2_release+0x1d7/0x3a0 drivers/media/v4l2-core/v4l2-dev.c:455
__fput+0x385/0xa30 fs/file_table.c:278
delayed_fput+0x55/0x80 fs/file_table.c:304
process_one_work+0xc90/0x1c40 kernel/workqueue.c:2153
worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
kthread+0x35a/0x440 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352

other info that might help us debug this:

Chain exists of:
&mdev->req_queue_mutex --> (wq_completion)"events" --> (delayed_fput_work).work

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock((delayed_fput_work).work);
lock((wq_completion)"events");
lock((delayed_fput_work).work);
lock(&mdev->req_queue_mutex);

*** DEADLOCK ***

2 locks held by kworker/0:2/3421:
#0: 00000000312444b2 ((wq_completion)"events"){+.+.}, at: __write_once_size include/linux/compiler.h:209 [inline]
#0: 00000000312444b2 ((wq_completion)"events"){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 00000000312444b2 ((wq_completion)"events"){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 00000000312444b2 ((wq_completion)"events"){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:59 [inline]
#0: 00000000312444b2 ((wq_completion)"events"){+.+.}, at: set_work_data kernel/workqueue.c:617 [inline]
#0: 00000000312444b2 ((wq_completion)"events"){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 00000000312444b2 ((wq_completion)"events"){+.+.}, at: process_one_work+0xb43/0x1c40 kernel/workqueue.c:2124
#1: 000000009258f90c ((delayed_fput_work).work){+.+.}, at: process_one_work+0xb9a/0x1c40 kernel/workqueue.c:2128
kobject: 'regulatory.0' (0000000078fe9404): kobject_uevent_env

stack backtrace:
CPU: 0 PID: 3421 Comm: kworker/0:2 Not tainted 4.20.0-rc2+ #338
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
kobject: 'regulatory.0' (0000000078fe9404): fill_kobj_path: path = '/devices/platform/regulatory.0'
Workqueue: events delayed_fput
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x244/0x39d lib/dump_stack.c:113
print_circular_bug.isra.35.cold.54+0x1bd/0x27d kernel/locking/lockdep.c:1221
check_prev_add kernel/locking/lockdep.c:1863 [inline]
check_prevs_add kernel/locking/lockdep.c:1976 [inline]
validate_chain kernel/locking/lockdep.c:2347 [inline]
__lock_acquire+0x3399/0x4c20 kernel/locking/lockdep.c:3341
lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3844
__mutex_lock_common kernel/locking/mutex.c:925 [inline]
__mutex_lock+0x166/0x16f0 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
v4l2_release+0x1d7/0x3a0 drivers/media/v4l2-core/v4l2-dev.c:455
__fput+0x385/0xa30 fs/file_table.c:278
delayed_fput+0x55/0x80 fs/file_table.c:304
process_one_work+0xc90/0x1c40 kernel/workqueue.c:2153
worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
kthread+0x35a/0x440 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
kobject: 'regulatory.0' (0000000078fe9404): kobject_uevent_env
kobject: 'regulatory.0' (0000000078fe9404): fill_kobj_path: path = '/devices/platform/regulatory.0'

Next message: Priit Laes: "Re: [PATCH v3 3/3] b43: Use cordic algorithm from kernel library"
Previous message: Joe Perches: "Re: [PATCH] arch/powerpc: Use dma_zalloc_coherent"
In reply to: syzbot: "possible deadlock in v4l2_release"
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