[ OK ] Reached target Graphical Interface. Starting Update UTMP about System Runlevel Changes... [ OK ] Started Update UTMP about System Runlevel Changes. Starting Load/Save RF Kill Switch Status... [ OK ] Started Load/Save RF Kill Switch Status. Debian GNU/Linux 9 syzkaller ttyS0 Warning: Permanently added '10.128.0.29' (ECDSA) to the list of known hosts. syzkaller login: [ 40.145759] IPVS: ftp: loaded support on port[0] = 21 executing program [ 40.204335] IPVS: ftp: loaded support on port[0] = 21 [ 40.293380] [ 40.295045] ====================================================== [ 40.301470] WARNING: possible circular locking dependency detected [ 40.307781] 4.19.161-syzkaller #0 Not tainted [ 40.312251] ------------------------------------------------------ [ 40.318557] kworker/u4:3/110 is trying to acquire lock: [ 40.323897] 00000000f710179f ((wq_completion)"events"){+.+.}, at: flush_workqueue+0xe8/0x13e0 [ 40.332565] [ 40.332565] but task is already holding lock: [ 40.338554] 00000000a7c48411 (pernet_ops_rwsem){++++}, at: cleanup_net+0xa8/0x8b0 [ 40.346301] [ 40.346301] which lock already depends on the new lock. [ 40.346301] [ 40.354617] [ 40.354617] the existing dependency chain (in reverse order) is: [ 40.362229] [ 40.362229] -> #3 (pernet_ops_rwsem){++++}: [ 40.368013] unregister_netdevice_notifier+0x7b/0x330 [ 40.374570] raw_release+0x58/0x820 [ 40.378785] __sock_release+0xcd/0x2a0 [ 40.383191] sock_close+0x15/0x20 [ 40.387145] __fput+0x2ce/0x890 [ 40.391282] task_work_run+0x148/0x1c0 [ 40.395676] exit_to_usermode_loop+0x251/0x2a0 [ 40.400768] do_syscall_64+0x538/0x620 [ 40.405152] entry_SYSCALL_64_after_hwframe+0x49/0xbe [ 40.410835] [ 40.410835] -> #2 (&sb->s_type->i_mutex_key#13){+.+.}: [ 40.418095] __sock_release+0x86/0x2a0 [ 40.422513] sock_close+0x15/0x20 [ 40.427421] __fput+0x2ce/0x890 [ 40.431235] delayed_fput+0x56/0x70 [ 40.435402] process_one_work+0x864/0x1570 [ 40.440172] worker_thread+0x64c/0x1130 [ 40.444648] kthread+0x33f/0x460 [ 40.448529] ret_from_fork+0x24/0x30 [ 40.452746] [ 40.452746] -> #1 ((delayed_fput_work).work){+.+.}: [ 40.459243] worker_thread+0x64c/0x1130 [ 40.463846] kthread+0x33f/0x460 [ 40.467709] ret_from_fork+0x24/0x30 [ 40.471915] [ 40.471915] -> #0 ((wq_completion)"events"){+.+.}: [ 40.478306] flush_workqueue+0x117/0x13e0 [ 40.482964] tipc_exit_net+0x38/0x60 [ 40.487193] ops_exit_list+0xa5/0x150 [ 40.491499] cleanup_net+0x3b4/0x8b0 [ 40.495749] process_one_work+0x864/0x1570 [ 40.500499] worker_thread+0x64c/0x1130 [ 40.505076] kthread+0x33f/0x460 [ 40.508947] ret_from_fork+0x24/0x30 [ 40.513676] [ 40.513676] other info that might help us debug this: [ 40.513676] [ 40.521888] Chain exists of: [ 40.521888] (wq_completion)"events" --> &sb->s_type->i_mutex_key#13 --> pernet_ops_rwsem [ 40.521888] [ 40.534642] Possible unsafe locking scenario: [ 40.534642] [ 40.540696] CPU0 CPU1 [ 40.545344] ---- ---- [ 40.550508] lock(pernet_ops_rwsem); [ 40.554287] lock(&sb->s_type->i_mutex_key#13); [ 40.561566] lock(pernet_ops_rwsem); [ 40.567858] lock((wq_completion)"events"); [ 40.572272] [ 40.572272] *** DEADLOCK *** [ 40.572272] [ 40.578332] 3 locks held by kworker/u4:3/110: [ 40.582819] #0: 000000000251fa38 ((wq_completion)"%s""netns"){+.+.}, at: process_one_work+0x767/0x1570 [ 40.592340] #1: 00000000b133b634 (net_cleanup_work){+.+.}, at: process_one_work+0x79c/0x1570 [ 40.601003] #2: 00000000a7c48411 (pernet_ops_rwsem){++++}, at: cleanup_net+0xa8/0x8b0 [ 40.609231] [ 40.609231] stack backtrace: [ 40.613932] CPU: 0 PID: 110 Comm: kworker/u4:3 Not tainted 4.19.161-syzkaller #0 [ 40.621443] Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 [ 40.630788] Workqueue: netns cleanup_net [ 40.634850] Call Trace: [ 40.637440] dump_stack+0x1fc/0x2fe [ 40.641153] print_circular_bug.constprop.0.cold+0x2d7/0x41e [ 40.646947] __lock_acquire+0x30c9/0x3ff0 [ 40.651515] ? lock_downgrade+0x720/0x720 [ 40.658603] ? mark_held_locks+0xf0/0xf0 [ 40.669616] ? check_preemption_disabled+0x41/0x280 [ 40.674627] lock_acquire+0x170/0x3c0 [ 40.678421] ? flush_workqueue+0xe8/0x13e0 [ 40.683589] flush_workqueue+0x117/0x13e0 [ 40.687716] ? flush_workqueue+0xe8/0x13e0 [ 40.692017] ? lock_downgrade+0x720/0x720 [ 40.696143] ? trace_hardirqs_off+0x64/0x200 [ 40.700550] ? check_flush_dependency+0x400/0x400 [ 40.705391] ? tipc_net_stop+0x15e/0x320 [ 40.709445] tipc_exit_net+0x38/0x60 [ 40.713154] ? __tipc_nl_media_set.cold+0x2b/0x2b [ 40.717991] ops_exit_list+0xa5/0x150 [ 40.721784] cleanup_net+0x3b4/0x8b0 [ 40.725502] ? net_drop_ns+0x90/0x90 [ 40.729649] ? check_preemption_disabled+0x10/0x280 [ 40.734648] process_one_work+0x864/0x1570 [ 40.738864] ? pwq_dec_nr_in_flight+0x2d0/0x2d0 [ 40.743515] worke