INFO: task hung in ext4_put_super

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 84bae26850e3 Linux 4.14.284
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=152651f8080000
kernel config: https://syzkaller.appspot.com/x/.config?x=3f2be884e0c5d592
dashboard link: https://syzkaller.appspot.com/bug?extid=b72286444ed8911555bf
compiler: gcc version 10.2.1 20210110 (Debian 10.2.1-6)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=108454c4080000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15b75c8ff00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b72286...@syzkaller.appspotmail.com

EXT4-fs (loop0): re-mounted. Opts: (null)
EXT4-fs (loop0): re-mounted. Opts: (null)
EXT4-fs (loop0): re-mounted. Opts: (null)
EXT4-fs (loop0): re-mounted. Opts: (null)
INFO: task syz-executor419:7971 blocked for more than 140 seconds.
Not tainted 4.14.284-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor419 D28344 7971 7969 0x00000000
Call Trace:
context_switch kernel/sched/core.c:2811 [inline]
__schedule+0x88b/0x1de0 kernel/sched/core.c:3387
schedule+0x8d/0x1b0 kernel/sched/core.c:3431
schedule_timeout+0x80a/0xe90 kernel/time/timer.c:1724
do_wait_for_common kernel/sched/completion.c:91 [inline]
__wait_for_common kernel/sched/completion.c:112 [inline]
wait_for_common+0x272/0x430 kernel/sched/completion.c:123
kthread_stop+0xce/0x640 kernel/kthread.c:555
ext4_put_super+0x865/0xf00 fs/ext4/super.c:988
generic_shutdown_super+0x144/0x370 fs/super.c:446
kill_block_super+0x95/0xe0 fs/super.c:1161
deactivate_locked_super+0x6c/0xd0 fs/super.c:319
deactivate_super+0x7f/0xa0 fs/super.c:350
cleanup_mnt+0x186/0x2c0 fs/namespace.c:1183
task_work_run+0x11f/0x190 kernel/task_work.c:113
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x1ad/0x200 arch/x86/entry/common.c:164
prepare_exit_to_usermode arch/x86/entry/common.c:199 [inline]
syscall_return_slowpath arch/x86/entry/common.c:270 [inline]
do_syscall_64+0x4a3/0x640 arch/x86/entry/common.c:297
entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x7f242229b3e7
RSP: 002b:00007ffe86c74948 EFLAGS: 00000206 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007f242229b3e7
RDX: 00007ffe86c74a0b RSI: 000000000000000a RDI: 00007ffe86c74a00
RBP: 00007ffe86c74a00 R08: 00000000ffffffff R09: 00007ffe86c747e0
R10: 0000555556100683 R11: 0000000000000206 R12: 00007ffe86c75a70
R13: 00005555561005f0 R14: 00007ffe86c74970 R15: 00000000000000f0

Showing all locks held in the system:
1 lock held by khungtaskd/1532:
#0: (tasklist_lock){.+.+}, at: [<ffffffff87028029>] debug_show_all_locks+0x7c/0x21a kernel/locking/lockdep.c:4548
1 lock held by syz-executor419/7971:
#0: (&type->s_umount_key#36){++++}, at: [<ffffffff81876b17>] deactivate_super+0x77/0xa0 fs/super.c:349

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

NMI backtrace for cpu 0
CPU: 0 PID: 1532 Comm: khungtaskd Not tainted 4.14.284-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x1b2/0x281 lib/dump_stack.c:58
nmi_cpu_backtrace.cold+0x57/0x93 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x13a/0x180 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:140 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
watchdog+0x5b9/0xb40 kernel/hung_task.c:274
kthread+0x30d/0x420 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff872480fe


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