INFO: task hung in locks_remove_posix

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syzbot

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May 20, 2020, 4:53:17 PM5/20/20

to andre...@google.com, bfi...@fieldses.org, jla...@kernel.org, linux-...@vger.kernel.org, linux-...@vger.kernel.org, linu...@vger.kernel.org, syzkall...@googlegroups.com, vi...@zeniv.linux.org.uk

Hello,

syzbot found the following crash on:

HEAD commit: 806d8acc USB: dummy-hcd: use configurable endpoint naming ..
git tree: https://github.com/google/kasan.git usb-fuzzer
console output: https://syzkaller.appspot.com/x/log.txt?x=16c9ece2100000
kernel config: https://syzkaller.appspot.com/x/.config?x=d800e9bad158025f
dashboard link: https://syzkaller.appspot.com/bug?extid=f5bc30abd8916982419c
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+f5bc30...@syzkaller.appspotmail.com

INFO: task syz-executor.2:3145 blocked for more than 143 seconds.
Not tainted 5.7.0-rc5-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.2 D28552 3145 370 0x80004006
Call Trace:
context_switch kernel/sched/core.c:3367 [inline]
__schedule+0x892/0x1d80 kernel/sched/core.c:4083
locks_remove_posix+0x277/0x4e0 fs/locks.c:2706
__sched_text_start+0x8/0x8
spin_unlock_irqrestore include/linux/spinlock.h:408 [inline]
prepare_to_wait_event+0x129/0x650 kernel/sched/wait.c:305
schedule+0xcd/0x2b0 kernel/sched/core.c:4158
wdm_flush+0x2ea/0x3c0 drivers/usb/class/cdc-wdm.c:590
wdm_poll+0x280/0x280 include/linux/poll.h:50
wait_for_completion+0x280/0x280
finish_wait+0x260/0x260 include/linux/list.h:301
task_work_add+0x97/0x120 kernel/task_work.c:35
wdm_poll+0x280/0x280 include/linux/poll.h:50
filp_close+0xb4/0x170 fs/open.c:1251
close_files fs/file.c:388 [inline]
put_files_struct fs/file.c:416 [inline]
put_files_struct+0x1d8/0x2e0 fs/file.c:413
exit_files+0x7e/0xa0 fs/file.c:445
do_exit+0xb36/0x2c80 kernel/exit.c:791
find_held_lock+0x2d/0x110 kernel/locking/lockdep.c:4458
mm_update_next_owner+0x7a0/0x7a0 kernel/exit.c:375
lock_downgrade+0x720/0x720 kernel/locking/lockdep.c:4599
do_group_exit+0x125/0x340 kernel/exit.c:894
get_signal+0x480/0x2480 kernel/signal.c:2739
schedule_timeout_idle+0x80/0x80 kernel/time/timer.c:1942
do_signal+0x88/0x1ae0 arch/x86/kernel/signal.c:784
free_object+0x5/0x70 lib/debugobjects.c:429
destroy_hrtimer_on_stack kernel/time/hrtimer.c:453 [inline]
hrtimer_nanosleep+0x211/0x3a0 kernel/time/hrtimer.c:1947
nanosleep_copyout+0x100/0x100 kernel/time/hrtimer.c:1861
force_valid_ss arch/x86/kernel/signal.c:73 [inline]
restore_sigcontext+0x620/0x620 arch/x86/kernel/signal.c:134
hrtimer_init_sleeper_on_stack+0x90/0x90 kernel/time/hrtimer.c:1833
put_old_itimerspec32+0x1d0/0x1d0 kernel/time/time.c:908
__do_sys_clock_gettime kernel/time/posix-timers.c:1094 [inline]
__se_sys_clock_gettime kernel/time/posix-timers.c:1082 [inline]
__x64_sys_clock_gettime+0x154/0x240 kernel/time/posix-timers.c:1082
__do_sys_nanosleep kernel/time/hrtimer.c:1962 [inline]
__se_sys_nanosleep kernel/time/hrtimer.c:1953 [inline]
__x64_sys_nanosleep+0x1ed/0x260 kernel/time/hrtimer.c:1953
hrtimer_nanosleep+0x3a0/0x3a0 kernel/time/hrtimer.c:1943
exit_to_usermode_loop+0x1a2/0x200 arch/x86/entry/common.c:161
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
do_syscall_64+0x4e0/0x5a0 arch/x86/entry/common.c:305
entry_SYSCALL_64_after_hwframe+0x49/0xb3
trace_hardirqs_off_caller+0x2b/0x200 kernel/trace/trace_preemptirq.c:67

Showing all locks held in the system:
1 lock held by khungtaskd/23:
#0: ffffffff87111260 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x264 kernel/locking/lockdep.c:5754
1 lock held by in:imklog/267:
#0: ffff8881d976d9f0 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:826

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

NMI backtrace for cpu 0
CPU: 0 PID: 23 Comm: khungtaskd Not tainted 5.7.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0xef/0x16e lib/dump_stack.c:118
irq_force_complete_move.cold+0x13/0x47 arch/x86/kernel/apic/vector.c:1023
nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101
lapic_can_unplug_cpu.cold+0x3b/0x3b
nmi_trigger_cpumask_backtrace+0x1db/0x207 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0xa99/0xfd0 kernel/hung_task.c:289
reset_hung_task_detector+0x30/0x30 kernel/hung_task.c:243
kthread+0x326/0x430 kernel/kthread.c:268
kthread_create_on_node+0xf0/0xf0 kernel/kthread.c:405
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:351
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:60 [inline]
NMI backtrace for cpu 1 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:103 [inline]
NMI backtrace for cpu 1 skipped: idling at default_idle+0x28/0x300 arch/x86/kernel/process.c:697

---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

Tetsuo Handa

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May 21, 2020, 10:09:48 AM5/21/20

to syzbot, syzkall...@googlegroups.com, linux-...@vger.kernel.org

On 2020/05/21 5:53, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 806d8acc USB: dummy-hcd: use configurable endpoint naming ..
> git tree: https://github.com/google/kasan.git usb-fuzzer
> console output: https://syzkaller.appspot.com/x/log.txt?x=16c9ece2100000
> kernel config: https://syzkaller.appspot.com/x/.config?x=d800e9bad158025f
> dashboard link: https://syzkaller.appspot.com/bug?extid=f5bc30abd8916982419c
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
>
> Unfortunately, I don't have any reproducer for this crash yet.

This seems to be a mislabeling due to '?' in all lines in a trace.

#syz dup: INFO: task hung in wdm_flush

Dmitry Vyukov

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May 21, 2020, 10:21:19 AM5/21/20

to Tetsuo Handa, syzbot, syzkaller-bugs, LKML

It seems that unwind from __schedule is broken. Fixing the unwinder
may be the action item here, otherwise we will get an infinite number
of such reports.

Jeff Layton

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May 21, 2020, 10:48:14 AM5/21/20

to Tetsuo Handa, syzbot, syzkall...@googlegroups.com, linux-...@vger.kernel.org

I'm not sure I trust those stack traces. The console output shows '?'
characters in front of every frame. Doesn't that mean that that address
it found on the stack is unreliable?

In principle, unless you're overriding the filp->lock operation (and the
wdm fs doesn't do that, afaict), locks_remove_posix should not block.
I'll also note that there is some of this in the logs before the hung
task warnings:

[ 182.020388][ T12] usb 5-1: too many endpoints for config 0 interface 107 altsetting 116: 116, using maximum allowed: 30
[ 182.031661][ T12] usb 5-1: config 0 interface 107 altsetting 116 has 0 endpoint descriptors, different from the interface descriptor's value: 116
[ 182.045145][ T12] usb 5-1: config 0 interface 107 has no altsetting 0
[ 182.052028][ T12] usb 5-1: New USB device found, idVendor=0926, idProduct=3333, bcdDevice= 0.40
[ 182.060120][ T3525] usb 6-1: USB disconnect, device number 20
[ 182.061148][ C0] xpad 6-1:0.65: xpad_irq_out - usb_submit_urb failed with result -19
[ 182.075465][ T3525] xpad 6-1:0.65: xpad_try_sending_next_out_packet - usb_submit_urb failed with result -19
[ 182.075565][ T12] usb 5-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0
[ 182.109020][ T12] usb 5-1: config 0 descriptor??
[ 182.136857][ T163] usb usb2-port1: attempt power cycle
[ 182.410396][ T4447] udc-core: couldn't find an available UDC or it's busy
[ 182.417562][ T4447] misc raw-gadget: fail, usb_gadget_probe_driver returned -16
[ 182.856513][ T163] usb 2-1: new high-speed USB device number 18 using dummy_hcd
[ 183.026601][ T163] usb 2-1: device descriptor read/8, error -61
[ 183.236577][ T163] usb 2-1: device descriptor read/8, error -71
[ 184.068991][ T3525] usb 5-1: USB disconnect, device number 21
[ 206.185571][ T23] INFO: task syz-executor.2:3145 blocked for more than 143 seconds.
[ 206.193630][ T23] Not tainted 5.7.0-rc5-syzkaller #0
[ 206.199512][ T23] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 206.208242][ T23] syz-executor.2 D28552 3145 370 0x80004006

...which leads me to believe that this might have more to do with the
USB subsystem than anything in the posix locking code.

In any case, I doubt there's much we can do here without a more reliable
stack trace to work from. That call stack doesn't seem to make much
sense.

--
Jeff Layton <jla...@kernel.org>

Andrey Konovalov

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May 21, 2020, 12:27:44 PM5/21/20

to Jeff Layton, Tetsuo Handa, syzbot, syzkaller-bugs, LKML

Most likely this is a duplicate of:

https://syzkaller.appspot.com/bug?id=e7b761593b23eb50855b9ea31e3be5472b711186

(with more than 30000 crashes now :)

Hillf Danton

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May 21, 2020, 10:57:53 PM5/21/20

to syzbot, andre...@google.com, bfi...@fieldses.org, jla...@kernel.org, linux-...@vger.kernel.org, linux-...@vger.kernel.org, linu...@vger.kernel.org, syzkall...@googlegroups.com, vi...@zeniv.linux.org.uk

Wed, 20 May 2020 13:53:15 -0700

Pair clear_bit() with wake_up() as wdm_flush() is waiting for the
WDM_IN_USE flag to go.

--- a/drivers/usb/class/cdc-wdm.c
+++ b/drivers/usb/class/cdc-wdm.c
@@ -424,6 +424,7 @@ static ssize_t wdm_write
if (rv < 0) {
desc->outbuf = NULL;
clear_bit(WDM_IN_USE, &desc->flags);
+ wake_up(&desc->wait);
dev_err(&desc->intf->dev, "Tx URB error: %d\n", rv);
rv = usb_translate_errors(rv);
goto out_free_mem_pm;

Tetsuo Handa

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May 24, 2020, 8:13:46 PM5/24/20

to syzbot, syzkaller-bugs

#syz undup

Tetsuo Handa

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May 24, 2020, 8:14:07 PM5/24/20

to syzbot, syzkaller-bugs

#syz fix: x86/unwind/orc: Fix unwind_get_return_address_ptr() for inactive tasks

syzbot

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May 24, 2020, 8:14:17 PM5/24/20

to andre...@google.com, bfi...@fieldses.org, dvy...@google.com, hda...@sina.com, jla...@kernel.org, linux-...@vger.kernel.org, linux-...@vger.kernel.org, linu...@vger.kernel.org, penguin...@i-love.sakura.ne.jp, penguin...@i-love.sakura.ne.jp, syzkall...@googlegroups.com, vi...@zeniv.linux.org.uk

syzbot has found a reproducer for the following crash on:

HEAD commit: 806d8acc USB: dummy-hcd: use configurable endpoint naming ..
git tree: https://github.com/google/kasan.git usb-fuzzer

console output: https://syzkaller.appspot.com/x/log.txt?x=1109c09a100000

kernel config: https://syzkaller.appspot.com/x/.config?x=d800e9bad158025f
dashboard link: https://syzkaller.appspot.com/bug?extid=f5bc30abd8916982419c
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=171ea49a100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f5bc30...@syzkaller.appspotmail.com

INFO: task syz-executor.1:3125 blocked for more than 143 seconds.

Not tainted 5.7.0-rc5-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor.1 D26504 3125 389 0x80004006

Call Trace:
context_switch kernel/sched/core.c:3367 [inline]
__schedule+0x892/0x1d80 kernel/sched/core.c:4083
locks_remove_posix+0x277/0x4e0 fs/locks.c:2706
__sched_text_start+0x8/0x8
spin_unlock_irqrestore include/linux/spinlock.h:408 [inline]
prepare_to_wait_event+0x129/0x650 kernel/sched/wait.c:305

__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
_raw_spin_unlock_irqrestore+0x39/0x40 kernel/locking/spinlock.c:191

schedule+0xcd/0x2b0 kernel/sched/core.c:4158
wdm_flush+0x2ea/0x3c0 drivers/usb/class/cdc-wdm.c:590
wdm_poll+0x280/0x280 include/linux/poll.h:50

putname+0xe1/0x120 fs/namei.c:259
lock_is_held include/linux/lockdep.h:406 [inline]
rcu_read_lock_sched_held+0x9c/0xd0 kernel/rcu/update.c:121
rcu_read_lock_bh_held+0xb0/0xb0 kernel/rcu/update.c:333
do_signal+0x88/0x1ae0 arch/x86/kernel/signal.c:784
putname+0xe1/0x120 fs/namei.c:259
do_sys_openat2+0x46c/0x7d0 fs/open.c:1158

force_valid_ss arch/x86/kernel/signal.c:73 [inline]
restore_sigcontext+0x620/0x620 arch/x86/kernel/signal.c:134

_copy_to_user+0x126/0x160 lib/usercopy.c:31
put_timespec64+0xcb/0x120 kernel/time/time.c:812
ns_to_kernel_old_timeval+0x100/0x100 kernel/time/time.c:521
do_sys_open+0xc3/0x140 fs/open.c:1164
filp_open+0x70/0x70 fs/open.c:1117

exit_to_usermode_loop+0x1a2/0x200 arch/x86/entry/common.c:161
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
do_syscall_64+0x4e0/0x5a0 arch/x86/entry/common.c:305
entry_SYSCALL_64_after_hwframe+0x49/0xb3

INFO: task syz-executor.2:3132 blocked for more than 143 seconds.

Not tainted 5.7.0-rc5-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor.2 D28552 3132 380 0x80004006

__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
_raw_spin_unlock_irqrestore+0x39/0x40 kernel/locking/spinlock.c:191

schedule+0xcd/0x2b0 kernel/sched/core.c:4158
wdm_flush+0x2ea/0x3c0 drivers/usb/class/cdc-wdm.c:590
wdm_poll+0x280/0x280 include/linux/poll.h:50

finish_wait+0x260/0x260 include/linux/list.h:301
task_work_add+0x97/0x120 kernel/task_work.c:35
wdm_poll+0x280/0x280 include/linux/poll.h:50
filp_close+0xb4/0x170 fs/open.c:1251
close_files fs/file.c:388 [inline]
put_files_struct fs/file.c:416 [inline]
put_files_struct+0x1d8/0x2e0 fs/file.c:413
exit_files+0x7e/0xa0 fs/file.c:445
do_exit+0xb36/0x2c80 kernel/exit.c:791
find_held_lock+0x2d/0x110 kernel/locking/lockdep.c:4458
mm_update_next_owner+0x7a0/0x7a0 kernel/exit.c:375
lock_downgrade+0x720/0x720 kernel/locking/lockdep.c:4599
do_group_exit+0x125/0x340 kernel/exit.c:894
get_signal+0x480/0x2480 kernel/signal.c:2739
schedule_timeout_idle+0x80/0x80 kernel/time/timer.c:1942
do_signal+0x88/0x1ae0 arch/x86/kernel/signal.c:784
free_object+0x5/0x70 lib/debugobjects.c:429
destroy_hrtimer_on_stack kernel/time/hrtimer.c:453 [inline]
hrtimer_nanosleep+0x211/0x3a0 kernel/time/hrtimer.c:1947
nanosleep_copyout+0x100/0x100 kernel/time/hrtimer.c:1861
force_valid_ss arch/x86/kernel/signal.c:73 [inline]
restore_sigcontext+0x620/0x620 arch/x86/kernel/signal.c:134
hrtimer_init_sleeper_on_stack+0x90/0x90 kernel/time/hrtimer.c:1833
put_old_itimerspec32+0x1d0/0x1d0 kernel/time/time.c:908

__do_sys_nanosleep kernel/time/hrtimer.c:1962 [inline]
__se_sys_nanosleep kernel/time/hrtimer.c:1953 [inline]
__x64_sys_nanosleep+0x1ed/0x260 kernel/time/hrtimer.c:1953
hrtimer_nanosleep+0x3a0/0x3a0 kernel/time/hrtimer.c:1943
exit_to_usermode_loop+0x1a2/0x200 arch/x86/entry/common.c:161
prepare_exit_to_usermode arch/x86/entry/common.c:196 [inline]
syscall_return_slowpath arch/x86/entry/common.c:279 [inline]
do_syscall_64+0x4e0/0x5a0 arch/x86/entry/common.c:305
entry_SYSCALL_64_after_hwframe+0x49/0xb3

INFO: task syz-executor.3:3150 blocked for more than 143 seconds.

Not tainted 5.7.0-rc5-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor.3 D29048 3150 386 0x80004006

__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
_raw_spin_unlock_irqrestore+0x39/0x40 kernel/locking/spinlock.c:191

schedule+0xcd/0x2b0 kernel/sched/core.c:4158
wdm_flush+0x2ea/0x3c0 drivers/usb/class/cdc-wdm.c:590
wdm_poll+0x280/0x280 include/linux/poll.h:50

down_interruptible+0x4b/0x80 kernel/locking/semaphore.c:85
do_signal+0x88/0x1ae0 arch/x86/kernel/signal.c:784
__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
_raw_spin_unlock_irqrestore+0x39/0x40 kernel/locking/spinlock.c:191
__trace_hardirqs_on_caller kernel/locking/lockdep.c:3657 [inline]
lockdep_hardirqs_on+0x3c7/0x5d0 kernel/locking/lockdep.c:3702

force_valid_ss arch/x86/kernel/signal.c:73 [inline]
restore_sigcontext+0x620/0x620 arch/x86/kernel/signal.c:134

down_interruptible+0x4b/0x80 kernel/locking/semaphore.c:85
raw_ioctl+0x11f/0x2570 drivers/usb/gadget/legacy/raw_gadget.c:1261
ksys_dup3+0x3c0/0x3c0 include/linux/compiler.h:199
raw_open+0x4d0/0x4d0 include/linux/semaphore.h:34
down_read_nested+0x430/0x430 include/linux/compiler.h:199

INFO: task syz-executor.4:3151 blocked for more than 143 seconds.

Not tainted 5.7.0-rc5-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor.4 D29048 3151 384 0x80004006

__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
_raw_spin_unlock_irqrestore+0x39/0x40 kernel/locking/spinlock.c:191

schedule+0xcd/0x2b0 kernel/sched/core.c:4158
wdm_flush+0x2ea/0x3c0 drivers/usb/class/cdc-wdm.c:590
wdm_poll+0x280/0x280 include/linux/poll.h:50

force_valid_ss arch/x86/kernel/signal.c:73 [inline]
restore_sigcontext+0x620/0x620 arch/x86/kernel/signal.c:134

INFO: task syz-executor.0:3152 blocked for more than 144 seconds.

Not tainted 5.7.0-rc5-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

syz-executor.0 D29048 3152 383 0x80004006

__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
_raw_spin_unlock_irqrestore+0x39/0x40 kernel/locking/spinlock.c:191

schedule+0xcd/0x2b0 kernel/sched/core.c:4158
wdm_flush+0x2ea/0x3c0 drivers/usb/class/cdc-wdm.c:590
wdm_poll+0x280/0x280 include/linux/poll.h:50

force_valid_ss arch/x86/kernel/signal.c:73 [inline]
restore_sigcontext+0x620/0x620 arch/x86/kernel/signal.c:134

Showing all locks held in the system:
1 lock held by khungtaskd/23:
#0: ffffffff87111260 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x264 kernel/locking/lockdep.c:5754

2 locks held by in:imklog/271:
#0: ffff8881c8468370 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:826
#1: ffffffff8719fce0 (fs_reclaim){+.+.}-{0:0}, at: fs_reclaim_acquire.part.0+0x0/0x30 include/asm-generic/bitops/instrumented-atomic.h:30

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

NMI backtrace for cpu 1
CPU: 1 PID: 23 Comm: khungtaskd Not tainted 5.7.0-rc5-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0xef/0x16e lib/dump_stack.c:118
irq_force_complete_move.cold+0x13/0x47 arch/x86/kernel/apic/vector.c:1023
nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101
lapic_can_unplug_cpu.cold+0x3b/0x3b
nmi_trigger_cpumask_backtrace+0x1db/0x207 lib/nmi_backtrace.c:62
trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0xa99/0xfd0 kernel/hung_task.c:289
reset_hung_task_detector+0x30/0x30 kernel/hung_task.c:243
kthread+0x326/0x430 kernel/kthread.c:268
kthread_create_on_node+0xf0/0xf0 kernel/kthread.c:405
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:351

Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:60 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:103 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle+0x28/0x300 arch/x86/kernel/process.c:697

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