[....] Starting enhanced syslogd: rsyslogd[?25l[?1c7[ ok 8[?25h[?0c.
[....] Starting periodic command scheduler: cron[?25l[?1c7[ ok 8[?25h[?0c.
[....] Starting OpenBSD Secure Shell server: sshd[?25l[?1c7[ ok 8[?25h[?0c.
[   28.359194] kauditd_printk_skb: 7 callbacks suppressed
[   28.359216] audit: type=1800 audit(1542499591.861:29): pid=5853 uid=0 auid=4294967295 ses=4294967295 subj==unconfined op=collect_data cause=failed(directio) comm="startpar" name="rc.local" dev="sda1" ino=2432 res=0
[   28.391233] 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

Debian GNU/Linux 7 syzkaller ttyS0

Warning: Permanently added '10.128.0.44' (ECDSA) to the list of known hosts.
executing program
syzkaller login: [   52.137616] 
[   52.139283] ======================================================
[   52.145577] WARNING: possible circular locking dependency detected
[   52.151874] 4.20.0-rc2+ #338 Not tainted
[   52.155941] ------------------------------------------------------
[   52.162239] kworker/0:1/12 is trying to acquire lock:
[   52.167641] 00000000568502c5 (&mdev->req_queue_mutex){+.+.}, at: v4l2_release+0x1d7/0x3a0
[   52.175955] 
[   52.175955] but task is already holding lock:
[   52.181904] 000000009d901cd4 ((delayed_fput_work).work){+.+.}, at: process_one_work+0xb9a/0x1c40
[   52.190817] 
[   52.190817] which lock already depends on the new lock.
[   52.190817] 
[   52.199126] 
[   52.199126] the existing dependency chain (in reverse order) is:
[   52.206738] 
[   52.206738] -> #3 ((delayed_fput_work).work){+.+.}:
[   52.213238]        process_one_work+0xc0a/0x1c40
[   52.217970]        worker_thread+0x17f/0x1390
[   52.222445]        kthread+0x35a/0x440
[   52.226309]        ret_from_fork+0x3a/0x50
[   52.230514] 
[   52.230514] -> #2 ((wq_completion)"events"){+.+.}:
[   52.236909]        flush_workqueue+0x30a/0x1e10
[   52.241558]        vim2m_stop_streaming+0x7c/0x2c0
[   52.246469]        __vb2_queue_cancel+0x171/0xd20
[   52.251292]        vb2_core_queue_release+0x26/0x80
[   52.256292]        vb2_queue_release+0x15/0x20
[   52.260857]        v4l2_m2m_ctx_release+0x1e/0x35
[   52.265679]        vim2m_release+0xe6/0x150
[   52.269980]        v4l2_release+0x224/0x3a0
[   52.274286]        __fput+0x385/0xa30
[   52.278139]        ____fput+0x15/0x20
[   52.281931]        task_work_run+0x1e8/0x2a0
[   52.286320]        exit_to_usermode_loop+0x318/0x380
[   52.291400]        do_syscall_64+0x6be/0x820
[   52.295789]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   52.301473] 
[   52.301473] -> #1 (&dev->dev_mutex){+.+.}:
[   52.307171]        __mutex_lock+0x166/0x16f0
[   52.311555]        mutex_lock_nested+0x16/0x20
[   52.316114]        vim2m_release+0xbc/0x150
[   52.320409]        v4l2_release+0x224/0x3a0
[   52.324716]        __fput+0x385/0xa30
[   52.328506]        ____fput+0x15/0x20
[   52.332284]        task_work_run+0x1e8/0x2a0
[   52.336671]        exit_to_usermode_loop+0x318/0x380
[   52.341751]        do_syscall_64+0x6be/0x820
[   52.346153]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
[   52.351835] 
[   52.351835] -> #0 (&mdev->req_queue_mutex){+.+.}:
[   52.358140]        lock_acquire+0x1ed/0x520
[   52.362437]        __mutex_lock+0x166/0x16f0
[   52.366822]        mutex_lock_nested+0x16/0x20
[   52.371385]        v4l2_release+0x1d7/0x3a0
[   52.375689]        __fput+0x385/0xa30
[   52.379470]        delayed_fput+0x55/0x80
[   52.383598]        process_one_work+0xc90/0x1c40
[   52.388330]        worker_thread+0x17f/0x1390
[   52.392802]        kthread+0x35a/0x440
[   52.396668]        ret_from_fork+0x3a/0x50
[   52.400873] 
[   52.400873] other info that might help us debug this:
[   52.400873] 
[   52.408988] Chain exists of:
[   52.408988]   &mdev->req_queue_mutex --> (wq_completion)"events" --> (delayed_fput_work).work
[   52.408988] 
[   52.421976]  Possible unsafe locking scenario:
[   52.421976] 
[   52.428008]        CPU0                    CPU1
[   52.432645]        ----                    ----
[   52.437300]   lock((delayed_fput_work).work);
[   52.441784]                                lock((wq_completion)"events");
[   52.448686]                                lock((delayed_fput_work).work);
[   52.455681]   lock(&mdev->req_queue_mutex);
[   52.459975] 
[   52.459975]  *** DEADLOCK ***
[   52.459975] 
[   52.466013] 2 locks held by kworker/0:1/12:
[   52.470326]  #0: 00000000809bd6ac ((wq_completion)"events"){+.+.}, at: process_one_work+0xb43/0x1c40
[   52.479598]  #1: 000000009d901cd4 ((delayed_fput_work).work){+.+.}, at: process_one_work+0xb9a/0x1c40
[   52.488939] 
[   52.488939] stack backtrace:
[   52.493417] CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 4.20.0-rc2+ #338
[   52.500319] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
[   52.509659] Workqueue: events delayed_fput
[   52.513871] Call Trace:
[   52.516440]  dump_stack+0x244/0x39d
[   52.520044]  ? dump_stack_print_info.cold.1+0x20/0x20
[   52.525213]  ? vprintk_func+0x85/0x181
[   52.529092]  print_circular_bug.isra.35.cold.54+0x1bd/0x27d
[   52.534784]  ? save_trace+0xe0/0x290
[   52.538477]  __lock_acquire+0x3399/0x4c20
[   52.542610]  ? mark_held_locks+0x130/0x130
[   52.546827]  ? __update_load_avg_blocked_se+0x690/0x690
[   52.552170]  ? __update_load_avg_se+0xae0/0xae0
[   52.556820]  ? print_usage_bug+0xc0/0xc0
[   52.560861]  ? lock_unpin_lock+0x4a0/0x4a0
[   52.565073]  ? update_load_avg+0x387/0x2470
[   52.569390]  ? find_held_lock+0x36/0x1c0
[   52.573432]  ? zap_class+0x640/0x640
[   52.577125]  ? __lock_acquire+0x62f/0x4c20
[   52.581359]  ? zap_class+0x640/0x640
[   52.585052]  ? mark_held_locks+0x130/0x130
[   52.589265]  ? add_timer+0x629/0x15a0
[   52.593047]  lock_acquire+0x1ed/0x520
[   52.596828]  ? v4l2_release+0x1d7/0x3a0
[   52.600797]  ? lock_release+0xa00/0xa00
[   52.604751]  ? perf_trace_sched_process_exec+0x860/0x860
[   52.610194]  ? print_usage_bug+0xc0/0xc0
[   52.614243]  ? v4l2_release+0x1d7/0x3a0
[   52.618197]  __mutex_lock+0x166/0x16f0
[   52.622069]  ? v4l2_release+0x1d7/0x3a0
[   52.626020]  ? v4l2_release+0x1d7/0x3a0
[   52.629976]  ? mutex_trylock+0x2b0/0x2b0
[   52.634015]  ? __lock_acquire+0x62f/0x4c20
[   52.638304]  ? mark_held_locks+0x130/0x130
[   52.642531]  ? mark_held_locks+0x130/0x130
[   52.646747]  ? mark_held_locks+0x130/0x130
[   52.650961]  ? lock_downgrade+0x900/0x900
[   52.655090]  ? check_preemption_disabled+0x48/0x280
[   52.660099]  ? zap_class+0x640/0x640
[   52.663790]  ? trace_event_raw_event_lock+0x340/0x340
[   52.668957]  ? zap_class+0x640/0x640
[   52.672651]  ? zap_class+0x640/0x640
[   52.676363]  ? __sanitizer_cov_trace_const_cmp4+0x16/0x20
[   52.681876]  ? fsnotify+0x50e/0xef0
[   52.685483]  ? __lock_is_held+0xb5/0x140
[   52.689522]  ? __sanitizer_cov_trace_const_cmp8+0x18/0x20
[   52.695038]  ? locks_remove_file+0x3c6/0x5c0
[   52.699425]  ? __sanitizer_cov_trace_const_cmp2+0x18/0x20
[   52.704938]  ? ima_file_free+0x132/0x650
[   52.708976]  ? fsnotify_first_mark+0x350/0x350
[   52.713537]  ? ima_file_check+0x130/0x130
[   52.717683]  ? vivid_remove+0x460/0x460
[   52.721640]  mutex_lock_nested+0x16/0x20
[   52.725684]  ? mutex_lock_nested+0x16/0x20
[   52.729904]  v4l2_release+0x1d7/0x3a0
[   52.733684]  ? dev_debug_store+0x140/0x140
[   52.737996]  __fput+0x385/0xa30
[   52.741269]  ? get_max_files+0x20/0x20
[   52.745141]  delayed_fput+0x55/0x80
[   52.748749]  process_one_work+0xc90/0x1c40
[   52.752965]  ? mark_held_locks+0x130/0x130
[   52.757182]  ? pwq_dec_nr_in_flight+0x4a0/0x4a0
[   52.761844]  ? __switch_to_asm+0x40/0x70
[   52.765882]  ? __switch_to_asm+0x34/0x70
[   52.769936]  ? __switch_to_asm+0x34/0x70
[   52.773972]  ? __switch_to_asm+0x40/0x70
[   52.778010]  ? __switch_to_asm+0x34/0x70
[   52.782047]  ? __switch_to_asm+0x40/0x70
[   52.786085]  ? __switch_to_asm+0x34/0x70
[   52.790137]  ? __switch_to_asm+0x40/0x70
[   52.794179]  ? __schedule+0x8d7/0x21d0
[   52.798047]  ? lock_downgrade+0x900/0x900
[   52.802173]  ? zap_class+0x640/0x640
[   52.805869]  ? find_held_lock+0x36/0x1c0
[   52.809912]  ? lock_acquire+0x1ed/0x520
[   52.813867]  ? worker_thread+0x3e0/0x1390
[   52.817998]  ? kasan_check_read+0x11/0x20
[   52.822125]  ? do_raw_spin_lock+0x14f/0x350
[   52.826424]  ? kasan_check_read+0x11/0x20
[   52.830557]  ? rwlock_bug.part.2+0x90/0x90
[   52.834784]  ? trace_hardirqs_on+0x310/0x310
[   52.839172]  worker_thread+0x17f/0x1390
[   52.843139]  ? __switch_to_asm+0x34/0x70
[   52.847177]  ? __switch_to_asm+0x40/0x70
[   52.851231]  ? __switch_to_asm+0x34/0x70
[   52.855275]  ? process_one_work+0x1c40/0x1c40
[   52.859754]  ? __sched_text_start+0x8/0x8
[   52.863885]  ? __kthread_parkme+0xce/0x1a0
[   52.868096]  ? _raw_spin_unlock_irqrestore+0x82/0xd0
[   52.873176]  ? _raw_spin_unlock_irqrestore+0x82/0xd0
[   52.878260]  ? lockdep_hardirqs_on+0x3bb/0x5b0
[   52.882822]  ? trace_hardirqs_on+0xbd/0x310
executing program
[   52.887138]  ? kasan_check_read+0x11/0x20
[   52.891267]  ? __kthread_parkme+0xce/0x1a0
[   52.895480]  ? trace_hardirqs_off_caller+0x310/0x310
[   52.900561]  ? _raw_spin_unlock_irqrestore+0x6d/0xd0
[   52.905650]  ? __sanitizer_cov_trace_const_cmp8+0x18/0x20
[   52.911184]  ? __kthread_parkme+0xfb/0x1a0
[   52.915399]  ? process_one_work+0x1c40/0x1c40
[   52.919871]  kthread+0x35a/0x440
[   52.923234]  ? kthread_stop+0x900/0x900
[   52.927190]  ret_from_fork+0x3a/0x50
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