INFO: task hung in tun_chr_close

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c14d30dc Linux 4.19.139
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15095f52900000
kernel config: https://syzkaller.appspot.com/x/.config?x=93b261233af4719e
dashboard link: https://syzkaller.appspot.com/bug?extid=eb210389a4b2417203f1
compiler: gcc (GCC) 10.1.0-syz 20200507

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+eb2103...@syzkaller.appspotmail.com

request_module: kmod_concurrent_max (0) close to 0 (max_modprobes: 50), for module nf-nat-0, throttling...
request_module: kmod_concurrent_max (0) close to 0 (max_modprobes: 50), for module nf-nat-0, throttling...
request_module: kmod_concurrent_max (0) close to 0 (max_modprobes: 50), for module nf-nat-0, throttling...
request_module: kmod_concurrent_max (0) close to 0 (max_modprobes: 50), for module nf-nat-0, throttling...
INFO: task syz-executor.1:3421 blocked for more than 140 seconds.
Not tainted 4.19.139-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.1 D26064 3421 6586 0x80000002
Call Trace:
context_switch kernel/sched/core.c:2828 [inline]
__schedule+0x887/0x2040 kernel/sched/core.c:3517
schedule+0x8d/0x1b0 kernel/sched/core.c:3561
schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:3619
__mutex_lock_common kernel/locking/mutex.c:1002 [inline]
__mutex_lock+0x647/0x1260 kernel/locking/mutex.c:1072
tun_detach drivers/net/tun.c:751 [inline]
tun_chr_close+0x3a/0x180 drivers/net/tun.c:3267
__fput+0x2ce/0x890 fs/file_table.c:278
task_work_run+0x148/0x1c0 kernel/task_work.c:113
exit_task_work include/linux/task_work.h:22 [inline]
do_exit+0xbb2/0x2b70 kernel/exit.c:887
do_group_exit+0x125/0x310 kernel/exit.c:990
get_signal+0x3f2/0x1f70 kernel/signal.c:2588
do_signal+0x8f/0x1670 arch/x86/kernel/signal.c:821
exit_to_usermode_loop+0x204/0x2a0 arch/x86/entry/common.c:163
prepare_exit_to_usermode arch/x86/entry/common.c:198 [inline]
syscall_return_slowpath arch/x86/entry/common.c:271 [inline]
do_syscall_64+0x538/0x620 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45ce69
Code: Bad RIP value.
RSP: 002b:00007fd2d7682c78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: 0000000000000080 RBX: 0000000000028580 RCX: 000000000045ce69
RDX: 0000000000000000 RSI: 0000000020000300 RDI: 0000000000000005
RBP: 000000000118bf60 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118bf2c
R13: 00007ffd0714fb9f R14: 00007fd2d76839c0 R15: 000000000118bf2c
INFO: task kworker/0:1:13693 blocked for more than 140 seconds.
Not tainted 4.19.139-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/0:1 D29632 13693 2 0x80000000
Workqueue: ipv6_addrconf addrconf_verify_work
Call Trace:
context_switch kernel/sched/core.c:2828 [inline]
__schedule+0x887/0x2040 kernel/sched/core.c:3517
schedule+0x8d/0x1b0 kernel/sched/core.c:3561


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[syzbot]

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