INFO: task hung in _rcu_barrier (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 225970c2 Merge 4.14.124 into android-4.14
git tree: android-4.14
console output: https://syzkaller.appspot.com/x/log.txt?x=13bf6c6aa00000
kernel config: https://syzkaller.appspot.com/x/.config?x=fa49f5528e613545
dashboard link: https://syzkaller.appspot.com/bug?extid=00b61d063344fa29ce09
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+00b61d...@syzkaller.appspotmail.com

INFO: task kworker/u4:0:28365 blocked for more than 140 seconds.
Not tainted 4.14.124+ #3
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:0 D26608 28365 2 0x80000000
Workqueue: netns cleanup_net
Call Trace:
schedule+0x92/0x1c0 kernel/sched/core.c:3498
schedule_timeout+0x736/0xe80 kernel/time/timer.c:1721
do_wait_for_common kernel/sched/completion.c:91 [inline]
__wait_for_common kernel/sched/completion.c:112 [inline]
wait_for_common+0x29c/0x470 kernel/sched/completion.c:123
_rcu_barrier+0x27b/0x3e0 kernel/rcu/tree.c:3611
cleanup_net+0x4a3/0x860 net/core/net_namespace.c:495
process_one_work+0x7c6/0x1510 kernel/workqueue.c:2134
worker_thread+0x5d7/0x1080 kernel/workqueue.c:2271
kthread+0x310/0x420 kernel/kthread.c:232
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:404

Showing all locks held in the system:
1 lock held by khungtaskd/23:
#0: (tasklist_lock){.+.+}, at: [<0000000079e999ba>]
debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4541
2 locks held by getty/1755:
#0: (&tty->ldisc_sem){++++}, at: [<000000005ab3424c>]
tty_ldisc_ref_wait+0x22/0x80 drivers/tty/tty_ldisc.c:284
#1: (&ldata->atomic_read_lock){+.+.}, at: [<00000000091b7bb4>]
n_tty_read+0x1f7/0x1700 drivers/tty/n_tty.c:2156
2 locks held by kworker/1:2/18427:
#0: ("events"){+.+.}, at: [<00000000741b5ea4>]
process_one_work+0x6e5/0x1510 kernel/workqueue.c:2105
#1: (key_gc_work){+.+.}, at: [<00000000aed9c109>]
process_one_work+0x71b/0x1510 kernel/workqueue.c:2109
3 locks held by kworker/u4:0/28365:
#0: ("%s""netns"){+.+.}, at: [<00000000741b5ea4>]
process_one_work+0x6e5/0x1510 kernel/workqueue.c:2105
#1: (net_cleanup_work){+.+.}, at: [<00000000aed9c109>]
process_one_work+0x71b/0x1510 kernel/workqueue.c:2109
#2: (rcu_preempt_state.barrier_mutex){+.+.}, at: [<00000000fce62f53>]
_rcu_barrier+0x56/0x3e0 kernel/rcu/tree.c:3546

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

NMI backtrace for cpu 1
CPU: 1 PID: 23 Comm: khungtaskd Not tainted 4.14.124+ #3
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0xb9/0x10e lib/dump_stack.c:53
nmi_cpu_backtrace.cold+0x47/0x86 lib/nmi_backtrace.c:101
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 19990 Comm: syz-executor.0 Not tainted 4.14.124+ #3
task: 00000000d915f1df task.stack: 0000000025192f41
RIP: 0033:0x4018eb
RSP: 002b:00007f3479863b50 EFLAGS: 00000206
RAX: 0000000023a3559f RBX: 0000000000000fff RCX: 0000000000459279
RDX: 0000000000412ea1 RSI: 0000000000a74ef0 RDI: 0000000000000043
RBP: 00000000004bdc54 R08: 000000000000000e R09: 0000000000000000
R10: 00007f3479864700 R11: 0000000000000246 R12: 0000000000000000
R13: 00000000004c673c R14: 00000000004db5e0 R15: 00000000ffffffff
FS: 00007f3479864700(0000) GS:ffff8881dba00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3479860fec CR3: 0000000190876002 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.