syzbot

audit: type=1800 audit(1542499591.861:30): pid=5853 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="rmnologin" dev="sda1" ino=2423 res=0

======================================================
WARNING: possible circular locking dependency detected
4.20.0-rc2+ #338 Not tainted
------------------------------------------------------
kworker/0:1/12 is trying to acquire lock:
00000000568502c5 (&mdev->req_queue_mutex){+.+.}, at: v4l2_release+0x1d7/0x3a0 drivers/media/v4l2-core/v4l2-dev.c:455

but task is already holding lock:
000000009d901cd4 ((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/0:1/12:
 #0: 00000000809bd6ac ((wq_completion)"events"){+.+.}, at: __write_once_size include/linux/compiler.h:209 [inline]
 #0: 00000000809bd6ac ((wq_completion)"events"){+.+.}, at: arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
 #0: 00000000809bd6ac ((wq_completion)"events"){+.+.}, at: atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline]
 #0: 00000000809bd6ac ((wq_completion)"events"){+.+.}, at: atomic_long_set include/asm-generic/atomic-long.h:59 [inline]
 #0: 00000000809bd6ac ((wq_completion)"events"){+.+.}, at: set_work_data kernel/workqueue.c:617 [inline]
 #0: 00000000809bd6ac ((wq_completion)"events"){+.+.}, at: set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0: 00000000809bd6ac ((wq_completion)"events"){+.+.}, at: process_one_work+0xb43/0x1c40 kernel/workqueue.c:2124
 #1: 000000009d901cd4 ((delayed_fput_work).work){+.+.}, at: process_one_work+0xb9a/0x1c40 kernel/workqueue.c:2128

stack backtrace:
CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 4.20.0-rc2+ #338
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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