INFO: task syz.5.585:10751 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.5.585       state:D stack:25128 pid:10751 tgid:10750 ppid:10433  task_flags:0x400140 flags:0x00004004
Call Trace:
 <TASK>
 __schedule+0x1798/0x4cc0
 schedule+0x165/0x360
 schedule_preempt_disabled+0x13/0x30
 rwsem_down_read_slowpath+0x5fd/0x8f0
 down_read+0x98/0x2e0
 super_lock+0x2a9/0x3b0
 __iterate_supers+0x126/0x290
 ksys_sync+0x94/0x150
 __ia32_sys_sync+0xe/0x20
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7efed558ec29
RSP: 002b:00007efed63bb038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a2
RAX: ffffffffffffffda RBX: 00007efed57d5fa0 RCX: 00007efed558ec29
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007efed57d5fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007efed57d6038 R14: 00007efed57d5fa0 R15: 00007ffcfc35af48
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/34:
 #0: ffffffff8e13a0e0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180
5 locks held by kworker/u10:5/1091:
2 locks held by getty/5677:
 #0: ffff888021cef0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70
 #1: ffffc900029062f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x43e/0x1400
3 locks held by kworker/0:5/5898:
 #0: ffff88801a480d48 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0
 #1: ffffc90003a3fbc0 ((work_completion)(&data->fib_event_work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0
 #2: ffff888023e5b240 (&data->fib_lock){+.+.}-{4:4}, at: nsim_fib_event_work+0x26b/0x3180
3 locks held by kworker/u8:5/7280:
 #0: ffff88801b2f7148 ((wq_completion)netns){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0
 #1: ffffc900029cfbc0 (net_cleanup_work){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0
 #2: ffffffff8f52d310 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xf7/0x800
2 locks held by syz-executor/8580:
1 lock held by syz.5.585/10751:
 #0: ffff88811d97a0e0 (&type->s_umount_key#51){++++}-{4:4}, at: super_lock+0x2a9/0x3b0
1 lock held by syz.9.667/11745:
 #0: ffff88811d97a0e0 (&type->s_umount_key#51){++++}-{4:4}, at: super_lock+0x25c/0x3b0
1 lock held by syz-executor/13518:
 #0: ffffffff8e13fb78 (rcu_state.exp_mutex){+.+.}-{4:4}, at: synchronize_rcu_expedited+0x3b9/0x730
2 locks held by syz-executor/13532:
 #0: ffffffff8e88f188 (bio_slab_lock){+.+.}-{4:4}, at: bioset_exit+0x44a/0x690
 #1: ffffffff8e13fa40 (rcu_state.barrier_mutex){+.+.}-{4:4}, at: rcu_barrier+0x4c/0x570
1 lock held by syz-executor/14078:
2 locks held by dhcpcd-run-hook/14081:

=============================================

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 34 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250
 nmi_cpu_backtrace+0x39e/0x3d0
 nmi_trigger_cpumask_backtrace+0x17a/0x300
 watchdog+0xf93/0xfe0
 kthread+0x711/0x8a0
 ret_from_fork+0x439/0x7d0
 ret_from_fork_asm+0x1a/0x30
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 7280 Comm: kworker/u8:5 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: netns cleanup_net
RIP: 0010:io_serial_in+0x77/0xc0
Code: e8 7e ff 6f fc 44 89 f9 d3 e3 49 83 c6 40 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 74 08 4c 89 f7 e8 cf 7c d3 fc 41 03 1e 89 da ec <0f> b6 c0 5b 41 5c 41 5e 41 5f e9 da 8d 2d 06 cc 44 89 f9 80 e1 07
RSP: 0018:ffffc900029ceff8 EFLAGS: 00000006
RAX: 1ffffffff33bf005 RBX: 00000000000003f9 RCX: 0000000000000000
RDX: 00000000000003f9 RSI: 0000000000000000 RDI: 0000000000000020
RBP: ffffc900029cf1d0 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: ffffffff854fadc0 R12: dffffc0000000000
R13: dffffc0000000000 R14: ffffffff99df8460 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881a3c12000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f68765efc18 CR3: 000000012d5d4000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 serial8250_console_write+0x584/0x1ba0
 console_flush_all+0x728/0xc40
 console_unlock+0xc4/0x270
 vprintk_emit+0x5b7/0x7a0
 _printk+0xcf/0x120
 netdev_info+0x10a/0x160
 netif_set_allmulti+0x1b8/0x380
 dev_set_allmulti+0x12b/0x260
 del_nbp+0xae/0xa60
 br_dev_delete+0x6e/0x100
 br_net_exit_rtnl+0xc1/0x140
 ops_undo_list+0x350/0x990
 cleanup_net+0x4c5/0x800
 process_scheduled_works+0xae1/0x17b0
 worker_thread+0x8a0/0xda0
 kthread+0x711/0x8a0
 ret_from_fork+0x439/0x7d0
 ret_from_fork_asm+0x1a/0x30
 </TASK>
