INFO: task hung in flush_to_ldisc

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: a844dc4c Linux 4.14.158
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1424fcb6e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=c02bef505ffc02ff
dashboard link: https://syzkaller.appspot.com/bug?extid=98b14ee3303a01afcf84
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+98b14e...@syzkaller.appspotmail.com

protocol 88fb is buggy, dev hsr_slave_1
protocol 88fb is buggy, dev hsr_slave_0
protocol 88fb is buggy, dev hsr_slave_1
protocol 88fb is buggy, dev hsr_slave_0
protocol 88fb is buggy, dev hsr_slave_1
INFO: task kworker/u4:2:88 blocked for more than 140 seconds.
Not tainted 4.14.158-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:2 D25952 88 2 0x80000000
Workqueue: events_unbound flush_to_ldisc
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
schedule+0x92/0x1c0 kernel/sched/core.c:3428
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3486
__mutex_lock_common kernel/locking/mutex.c:833 [inline]
__mutex_lock+0x73c/0x1470 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
flush_to_ldisc+0x39/0x400 drivers/tty/tty_buffer.c:499
process_one_work+0x863/0x1600 kernel/workqueue.c:2114
worker_thread+0x5d9/0x1050 kernel/workqueue.c:2248
kthread+0x319/0x430 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404
INFO: task getty:7030 blocked for more than 140 seconds.
Not tainted 4.14.158-syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
getty D28096 7030 1 0x80000002
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x7b8/0x1cd0 kernel/sched/core.c:3384
schedule+0x92/0x1c0 kernel/sched/core.c:3428
schedule_timeout+0x93b/0xe10 kernel/time/timer.c:1723
down_write_failed drivers/tty/tty_ldsem.c:298 [inline]
__ldsem_down_write_nested+0x304/0x7b0 drivers/tty/tty_ldsem.c:360
ldsem_down_write+0x33/0x39 drivers/tty/tty_ldsem.c:402
__tty_ldisc_lock drivers/tty/tty_ldisc.c:332 [inline]
tty_ldisc_lock+0x1e/0x50 drivers/tty/tty_ldisc.c:351
tty_ldisc_hangup+0x1a5/0x5e0 drivers/tty/tty_ldisc.c:751
__tty_hangup.part.0+0x2d3/0x6d0 drivers/tty/tty_io.c:622
__tty_hangup drivers/tty/tty_io.c:572 [inline]
tty_vhangup_session+0x25/0x30 drivers/tty/tty_io.c:732
disassociate_ctty.part.0+0x9b/0x6c0 drivers/tty/tty_jobctrl.c:266
disassociate_ctty+0x78/0x90 drivers/tty/tty_jobctrl.c:260
do_exit+0x1799/0x2c80 kernel/exit.c:852
do_group_exit+0x111/0x330 kernel/exit.c:951
SYSC_exit_group kernel/exit.c:962 [inline]
SyS_exit_group+0x1d/0x20 kernel/exit.c:960
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x7f13ad6941e8
RSP: 002b:00007ffdc5e59d58 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000001 RCX: 00007f13ad6941e8
RDX: 0000000000000001 RSI: 000000000000003c RDI: 0000000000000001
RBP: 00007f13ad969840 R08: 00000000000000e7 R09: ffffffffffffffa8
R10: 00007f13ad96f740 R11: 0000000000000246 R12: 00007f13ad969840
R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000000

Showing all locks held in the system:
3 locks held by kworker/u4:2/88:
#0: ("events_unbound"){+.+.}, at: [<ffffffff813d581e>] work_static
include/linux/workqueue.h:199 [inline]
#0: ("events_unbound"){+.+.}, at: [<ffffffff813d581e>] set_work_data
kernel/workqueue.c:619 [inline]
#0: ("events_unbound"){+.+.}, at: [<ffffffff813d581e>]
set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline]
#0: ("events_unbound"){+.+.}, at: [<ffffffff813d581e>]
process_one_work+0x76e/0x1600 kernel/workqueue.c:2085
#1: ((&buf->work)){+.+.}, at: [<ffffffff813d585b>]
process_one_work+0x7ab/0x1600 kernel/workqueue.c:2089
#2: (&buf->lock){+.+.}, at: [<ffffffff8349fcd9>]
flush_to_ldisc+0x39/0x400 drivers/tty/tty_buffer.c:499
1 lock held by khungtaskd/1045:
#0: (tasklist_lock){.+.+}, at: [<ffffffff8148c8a8>]
debug_show_all_locks+0x7f/0x21f kernel/locking/lockdep.c:4544
2 locks held by getty/7030:
#0: (&tty->legacy_mutex){+.+.}, at: [<ffffffff834a33d8>]
tty_lock+0x68/0x80 drivers/tty/tty_mutex.c:19
#1: (&tty->ldisc_sem){++++}, at: [<ffffffff86654a03>]
ldsem_down_write+0x33/0x39 drivers/tty/tty_ldsem.c:402
2 locks held by getty/7031:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/7032:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/7033:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/7034:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/7035:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156
2 locks held by getty/7036:
#0: (&tty->ldisc_sem){++++}, at: [<ffffffff866549c3>]
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:376
#1: (&ldata->atomic_read_lock){+.+.}, at: [<ffffffff83490d76>]
n_tty_read+0x1e6/0x17b0 drivers/tty/n_tty.c:2156

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

NMI backtrace for cpu 0
CPU: 0 PID: 1045 Comm: khungtaskd Not tainted 4.14.158-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+0x142/0x197 lib/dump_stack.c:58
nmi_cpu_backtrace.cold+0x57/0x94 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x141/0x189 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:140 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:195 [inline]
watchdog+0x5e7/0xb90 kernel/hung_task.c:274
kthread+0x319/0x430 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
CPU: 1 PID: 22765 Comm: syz-executor.1 Not tainted 4.14.158-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
task: ffff88809b9f0280 task.stack: ffff8880a13f8000
RIP: 0010:__lock_is_held+0x83/0x140 kernel/locking/lockdep.c:3811
RSP: 0018:ffff8880a13ff7d0 EFLAGS: 00000046
RAX: 0000000000000000 RBX: ffff88809b9f0280 RCX: ffff88809b9f0b00
RDX: 0000000000000000 RSI: ffffffff87f88820 RDI: ffff88809b9f0b4a
RBP: ffff8880a13ff810 R08: ffff88809b9f0280 R09: ffff88809b9f0b48
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff87f88820
R13: ffffed101373e15f R14: 0000000000000001 R15: ffff88809b9f0b28
FS: 00007f76c1b9c700(0000) GS:ffff8880aed00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000238c000 CR3: 000000009f33e000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
lock_is_held_type+0x110/0x210 kernel/locking/lockdep.c:4032
lock_is_held include/linux/lockdep.h:437 [inline]
rcu_read_lock_sched_held+0x110/0x130 kernel/rcu/update.c:116
trace_rcu_utilization include/trace/events/rcu.h:21 [inline]
trace_rcu_utilization include/trace/events/rcu.h:21 [inline]
rcu_note_context_switch+0xb6a/0x1600 kernel/rcu/tree.c:456
__schedule+0x1d2/0x1cd0 kernel/sched/core.c:3314
schedule+0x92/0x1c0 kernel/sched/core.c:3428
paste_selection+0x293/0x3f2 drivers/tty/vt/selection.c:355
tioclinux+0x10e/0x400 drivers/tty/vt/vt.c:2696
vt_ioctl+0x180c/0x2170 drivers/tty/vt/vt_ioctl.c:364
tty_ioctl+0x841/0x1320 drivers/tty/tty_io.c:2661
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:500 [inline]
do_vfs_ioctl+0x7ae/0x1060 fs/ioctl.c:684
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x45a909
RSP: 002b:00007f76c1b9bc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a909
RDX: 0000000020000000 RSI: 000000000000541c RDI: 0000000000000005
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f76c1b9c6d4
R13: 00000000004c5c62 R14: 00000000004dbf18 R15: 00000000ffffffff
Code: 31 f6 48 89 45 d0 48 b8 00 00 00 00 00 fc ff df 49 c1 ed 03 49 01 c5
8b 83 78 08 00 00 85 c0 7f 23 e9 88 00 00 00 41 0f b6 45 00 <41> 83 c6 01
84 c0 74 08 3c 03 0f 8e 92 00 00 00 44 39 b3 78 08


---
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.

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 312017a4 Linux 4.19.89
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16435c99e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=67c148d572dbab48
dashboard link: https://syzkaller.appspot.com/bug?extid=bc44024ce696c8867cba

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+bc4402...@syzkaller.appspotmail.com

RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 00007f4dbfa346d4
R13: 00000000004c5ca8 R14: 00000000004dbf60 R15: 0000000000000004
selection: kmalloc() failed
INFO: task kworker/u4:5:8122 blocked for more than 140 seconds.
Not tainted 4.19.89-syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

kworker/u4:5 D25160 8122 2 0x80000000

Workqueue: events_unbound flush_to_ldisc
Call Trace:

context_switch kernel/sched/core.c:2826 [inline]
__schedule+0x866/0x1dc0 kernel/sched/core.c:3515
schedule+0x92/0x1c0 kernel/sched/core.c:3559
schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3617
__mutex_lock_common kernel/locking/mutex.c:1002 [inline]
__mutex_lock+0x726/0x1300 kernel/locking/mutex.c:1072
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
flush_to_ldisc+0x3d/0x390 drivers/tty/tty_buffer.c:500
process_one_work+0x989/0x1750 kernel/workqueue.c:2153
worker_thread+0x98/0xe40 kernel/workqueue.c:2296
kthread+0x354/0x420 kernel/kthread.c:246
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415
INFO: task login:29371 blocked for more than 140 seconds.
Not tainted 4.19.89-syzkaller #0

"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

login D26992 29371 1 0x00000004
Call Trace:
context_switch kernel/sched/core.c:2826 [inline]
__schedule+0x866/0x1dc0 kernel/sched/core.c:3515
schedule+0x92/0x1c0 kernel/sched/core.c:3559
schedule_timeout+0x8c8/0xfc0 kernel/time/timer.c:1782
do_wait_for_common kernel/sched/completion.c:83 [inline]
__wait_for_common kernel/sched/completion.c:104 [inline]
wait_for_common kernel/sched/completion.c:115 [inline]
wait_for_completion+0x29c/0x440 kernel/sched/completion.c:136
__flush_work+0x49f/0x870 kernel/workqueue.c:2920
flush_work+0x18/0x20 kernel/workqueue.c:2941
tty_buffer_flush_work+0x16/0x19 drivers/tty/tty_buffer.c:613
n_tty_read+0xb1a/0x1b70 drivers/tty/n_tty.c:2197
tty_read+0x193/0x2a0 drivers/tty/tty_io.c:867
__vfs_read+0x114/0x800 fs/read_write.c:416
vfs_read+0x194/0x3d0 fs/read_write.c:452
ksys_read+0x14f/0x2d0 fs/read_write.c:579
__do_sys_read fs/read_write.c:589 [inline]
__se_sys_read fs/read_write.c:587 [inline]
__x64_sys_read+0x73/0xb0 fs/read_write.c:587
do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7ff8c671c310
Code: Bad RIP value.
RSP: 002b:00007ffc41dc9598 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff8c671c310
RDX: 00000000000001ff RSI: 00007ffc41dc9800 RDI: 0000000000000000
RBP: 0000000000000000 R08: 00007ff8c6fff700 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffc41dc9800
R13: 0000000000000000 R14: 0000000000000001 R15: 000000000060b798

Showing all locks held in the system:

1 lock held by khungtaskd/1068:
#0: 000000000ba36c9c (rcu_read_lock){....}, at:
debug_show_all_locks+0x5f/0x27e kernel/locking/lockdep.c:4438
3 locks held by rs:main Q:Reg/7680:
#0: 0000000027477893 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110
fs/file.c:767
#1: 00000000437fdee8 (sb_writers#4){.+.+}, at: file_start_write
include/linux/fs.h:2775 [inline]
#1: 00000000437fdee8 (sb_writers#4){.+.+}, at: vfs_write+0x429/0x560
fs/read_write.c:548
#2: 00000000099bd4db (&sb->s_type->i_mutex_key#9){++++}, at: inode_lock
include/linux/fs.h:747 [inline]
#2: 00000000099bd4db (&sb->s_type->i_mutex_key#9){++++}, at:
__generic_file_fsync+0xb5/0x200 fs/libfs.c:985
1 lock held by rsyslogd/7682:
#0: 00000000c7e12a64 (&f->f_pos_lock){+.+.}, at: __fdget_pos+0xee/0x110
fs/file.c:767
2 locks held by getty/7805:
#0: 00000000cc65e496 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 000000008b1506cc (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7806:
#0: 00000000214b1019 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 000000008453f1e0 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7807:
#0: 000000000931bf6b (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 000000001c0a70b7 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7808:
#0: 0000000050b7ec4b (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 00000000cc65e48d (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7809:
#0: 00000000739cd22f (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 000000001db64476 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by getty/7810:
#0: 000000009e8b16b6 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 000000000470c4fd (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
3 locks held by kworker/u4:5/8122:
#0: 0000000099423fb5 ((wq_completion)"events_unbound"){+.+.}, at:
__write_once_size include/linux/compiler.h:220 [inline]
#0: 0000000099423fb5 ((wq_completion)"events_unbound"){+.+.}, at:
arch_atomic64_set arch/x86/include/asm/atomic64_64.h:34 [inline]
#0: 0000000099423fb5 ((wq_completion)"events_unbound"){+.+.}, at:
atomic64_set include/asm-generic/atomic-instrumented.h:40 [inline]
#0: 0000000099423fb5 ((wq_completion)"events_unbound"){+.+.}, at:
atomic_long_set include/asm-generic/atomic-long.h:59 [inline]
#0: 0000000099423fb5 ((wq_completion)"events_unbound"){+.+.}, at:
set_work_data kernel/workqueue.c:617 [inline]
#0: 0000000099423fb5 ((wq_completion)"events_unbound"){+.+.}, at:
set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
#0: 0000000099423fb5 ((wq_completion)"events_unbound"){+.+.}, at:
process_one_work+0x87e/0x1750 kernel/workqueue.c:2124
#1: 0000000024c7a979 ((work_completion)(&buf->work)){+.+.}, at:
process_one_work+0x8b4/0x1750 kernel/workqueue.c:2128
#2: 00000000eae5f5bf (&buf->lock){+.+.}, at: flush_to_ldisc+0x3d/0x390
drivers/tty/tty_buffer.c:500
2 locks held by login/29371:
#0: 000000001124aa93 (&tty->ldisc_sem){++++}, at:
ldsem_down_read+0x33/0x40 drivers/tty/tty_ldsem.c:362
#1: 000000000bf9c955 (&ldata->atomic_read_lock){+.+.}, at:
n_tty_read+0x232/0x1b70 drivers/tty/n_tty.c:2154
2 locks held by syz-executor.4/29914:

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

NMI backtrace for cpu 0

CPU: 0 PID: 1068 Comm: khungtaskd Not tainted 4.19.89-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+0x197/0x210 lib/dump_stack.c:118
nmi_cpu_backtrace.cold+0x63/0xa4 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x1b0/0x1f8 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:146 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:203 [inline]
watchdog+0x9df/0xee0 kernel/hung_task.c:287
kthread+0x354/0x420 kernel/kthread.c:246
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1

CPU: 1 PID: 29914 Comm: syz-executor.4 Not tainted 4.19.89-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011

RIP: 0010:__lock_acquire+0x351/0x49c0 kernel/locking/lockdep.c:3352
Code: b2 0d 00 00 0f b7 48 20 81 e1 ff 1f 00 00 44 39 d9 75 0f 48 83 bc 24
98 00 00 00 00 0f 85 e3 07 00 00 4c 03 94 24 88 00 00 00 <44> 89 d9 66 81
e1 ff 1f 49 8d 42 20 48 89 c2 48 89 84 24 80 00 00
RSP: 0018:ffff8880785e7410 EFLAGS: 00000086
RAX: ffff888043fd6b90 RBX: 0000000000000000 RCX: 000000000000002c
RDX: 0000000000000000 RSI: 1ffff110087fad76 RDI: ffff888043fd6bb0
RBP: ffff8880785e75e0 R08: 0000000000000000 R09: 0000000000000003
R10: ffff888043fd6bb8 R11: 000000000000002d R12: 0000000000000002
R13: 0000000000000001 R14: ffff888043fd62c0 R15: ffffffff88f97320
FS: 00007f209b75f700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: ffffffffff600400 CR3: 000000009939f000 CR4: 00000000001406e0

DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:

lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:3903
rcu_lock_acquire include/linux/rcupdate.h:242 [inline]
rcu_read_lock include/linux/rcupdate.h:627 [inline]
cpuacct_charge+0xa7/0x360 kernel/sched/cpuacct.c:347
cgroup_account_cputime include/linux/cgroup.h:766 [inline]
update_curr+0x2d7/0x8a0 kernel/sched/fair.c:829
pick_next_task_fair+0x6bf/0x1580 kernel/sched/fair.c:6698
pick_next_task kernel/sched/core.c:3361 [inline]
__schedule+0x456/0x1dc0 kernel/sched/core.c:3489
schedule+0x92/0x1c0 kernel/sched/core.c:3559
paste_selection+0x2e8/0x443 drivers/tty/vt/selection.c:354
tioclinux+0x133/0x470 drivers/tty/vt/vt.c:3019
vt_ioctl+0x19ab/0x2530 drivers/tty/vt/vt_ioctl.c:364
tty_ioctl+0x7f3/0x1510 drivers/tty/tty_io.c:2669
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:501 [inline]
do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:688
ksys_ioctl+0xab/0xd0 fs/ioctl.c:705
__do_sys_ioctl fs/ioctl.c:712 [inline]
__se_sys_ioctl fs/ioctl.c:710 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:710
do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a909
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f209b75ec78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010

RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a909

RDX: 0000000020000080 RSI: 000000000000541c RDI: 0000000000000003

RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 00007f209b75f6d4
R13: 00000000004c5ca8 R14: 00000000004dbf60 R15: 00000000ffffffff

[syzbot]

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

[syzbot]