INFO: task hung in SyS_sync_file_range

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
3eb2ce825ea1ad89d20f7a3b5780df850e4be274 (Sun Mar 25 22:44:30 2018 +0000)
Linux 4.16-rc7
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=e19265ff646b0be033eb

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=6378606045429760
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-8440362230543204781
compiler: gcc (GCC) 7.1.1 20170620
CC: [ak...@linux-foundation.org arya...@virtuozzo.com ja...@suse.cz
jla...@redhat.com linux-...@vger.kernel.org linu...@kvack.org
mgo...@techsingularity.net rgol...@suse.com vi...@zeniv.linux.org.uk]

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e19265...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.

Buffer I/O error on dev loop0, logical block 64, async page read
INFO: task syz-executor0:30591 blocked for more than 120 seconds.
Not tainted 4.16.0-rc7+ #368
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor0 D26880 30591 9888 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2862 [inline]
__schedule+0x8fb/0x1ec0 kernel/sched/core.c:3440
schedule+0xf5/0x430 kernel/sched/core.c:3499
io_schedule+0x1c/0x70 kernel/sched/core.c:5115
wait_on_page_bit_common+0x4b3/0x770 mm/filemap.c:1099
wait_on_page_bit mm/filemap.c:1132 [inline]
wait_on_page_writeback include/linux/pagemap.h:546 [inline]
__filemap_fdatawait_range+0x282/0x430 mm/filemap.c:533
file_fdatawait_range+0x47/0x60 mm/filemap.c:581
SYSC_sync_file_range fs/sync.c:341 [inline]
SyS_sync_file_range+0x1e3/0x210 fs/sync.c:283
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x454889
RSP: 002b:00007f4601612c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000115
RAX: ffffffffffffffda RBX: 00007f46016136d4 RCX: 0000000000454889
RDX: 0000000000000000 RSI: 0000000000000002 RDI: 0000000000000014
RBP: 000000000072bf58 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000007 R11: 0000000000000246 R12: 00000000ffffffff
R13: 000000000000064c R14: 00000000006fb7c0 R15: 0000000000000001

Showing all locks held in the system:
3 locks held by kworker/u4:1/21:
#0: ((wq_completion)"writeback"){+.+.}, at: [<000000006e4d2945>]
work_static include/linux/workqueue.h:198 [inline]
#0: ((wq_completion)"writeback"){+.+.}, at: [<000000006e4d2945>]
set_work_data kernel/workqueue.c:619 [inline]
#0: ((wq_completion)"writeback"){+.+.}, at: [<000000006e4d2945>]
set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
#0: ((wq_completion)"writeback"){+.+.}, at: [<000000006e4d2945>]
process_one_work+0xb12/0x1bb0 kernel/workqueue.c:2084
#1: ((work_completion)(&(&wb->dwork)->work)){+.+.}, at:
[<000000001f087839>] process_one_work+0xb89/0x1bb0 kernel/workqueue.c:2088
#2: (&type->s_umount_key#33){.+.+}, at: [<000000002b169a1e>]
trylock_super+0x20/0x100 fs/super.c:395
2 locks held by khungtaskd/870:
#0: (rcu_read_lock){....}, at: [<00000000125c079d>]
check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline]
#0: (rcu_read_lock){....}, at: [<00000000125c079d>] watchdog+0x1c5/0xd60
kernel/hung_task.c:249
#1: (tasklist_lock){.+.+}, at: [<00000000d3177be7>]
debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470
2 locks held by getty/4419:
#0: (&tty->ldisc_sem){++++}, at: [<0000000031c19fd0>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000009442e5b9>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4420:
#0: (&tty->ldisc_sem){++++}, at: [<0000000031c19fd0>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000009442e5b9>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4421:
#0: (&tty->ldisc_sem){++++}, at: [<0000000031c19fd0>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000009442e5b9>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4422:
#0: (&tty->ldisc_sem){++++}, at: [<0000000031c19fd0>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000009442e5b9>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4423:
#0: (&tty->ldisc_sem){++++}, at: [<0000000031c19fd0>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000009442e5b9>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4424:
#0: (&tty->ldisc_sem){++++}, at: [<0000000031c19fd0>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000009442e5b9>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131
2 locks held by getty/4425:
#0: (&tty->ldisc_sem){++++}, at: [<0000000031c19fd0>]
ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365
#1: (&ldata->atomic_read_lock){+.+.}, at: [<000000009442e5b9>]
n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131

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

NMI backtrace for cpu 0
CPU: 0 PID: 870 Comm: khungtaskd Not tainted 4.16.0-rc7+ #368
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+0x194/0x24d lib/dump_stack.c:53
nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x123/0x180 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline]
check_hung_task kernel/hung_task.c:132 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline]
watchdog+0x90c/0xd60 kernel/hung_task.c:249
kthread+0x33c/0x400 kernel/kthread.c:238
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt+0x6/0x10
arch/x86/include/asm/irqflags.h:54


---
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[Dmitry Vyukov]

There were some cgroup-related changes around that time that caused
high rate of cgroup creation. Since cgroups are destroyed
asynchronously, they can cause such hangs. That was changed long time
ago.

#syz invalid

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