INFO: rcu detected stall in chrdev_open (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 258f0cf7 Linux 4.19.123
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10bec6aa100000
kernel config: https://syzkaller.appspot.com/x/.config?x=b296d33c12741d24
dashboard link: https://syzkaller.appspot.com/bug?extid=85f0300646d91bc20400
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+85f030...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: (detected by 1, t=10502 jiffies, g=31369, q=14)
rcu: All QSes seen, last rcu_preempt kthread activity 10503 (4294984069-4294973566), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor.2 R running task 27184 15570 6719 0x00000000
Call Trace:
<IRQ>
sched_show_task kernel/sched/core.c:5338 [inline]
sched_show_task.cold+0x2e2/0x343 kernel/sched/core.c:5313
print_other_cpu_stall kernel/rcu/tree.c:1430 [inline]
check_cpu_stall kernel/rcu/tree.c:1557 [inline]
__rcu_pending kernel/rcu/tree.c:3293 [inline]
rcu_pending kernel/rcu/tree.c:3336 [inline]
rcu_check_callbacks.cold+0xaf0/0xddc kernel/rcu/tree.c:2682
update_process_times+0x2a/0x70 kernel/time/timer.c:1638
tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:168
tick_sched_timer+0x42/0x130 kernel/time/tick-sched.c:1278
__run_hrtimer kernel/time/hrtimer.c:1401 [inline]
__hrtimer_run_queues+0x2fc/0xd50 kernel/time/hrtimer.c:1463
hrtimer_interrupt+0x312/0x770 kernel/time/hrtimer.c:1521
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1067 [inline]
smp_apic_timer_interrupt+0x10c/0x550 arch/x86/kernel/apic/apic.c:1092
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:894
</IRQ>
RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x50/0x80 kernel/locking/spinlock.c:192
Code: c0 d8 56 d2 88 48 ba 00 00 00 00 00 fc ff df 48 c1 e8 03 80 3c 10 00 75 31 48 83 3d b1 ac b0 01 00 74 25 fb 66 0f 1f 44 00 00 <bf> 01 00 00 00 e8 66 13 25 fa 65 8b 05 8f 43 e0 78 85 c0 74 02 5d
RSP: 0018:ffff888043d277c0 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff11a4adb RBX: ffff88804fb2a660 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffff88804fb2a8c4
RBP: ffff8880ae72c280 R08: ffff88804fb2a040 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88804fb2a040
R13: ffffffff878a5820 R14: ffff88804fb2a040 R15: ffff8880ae72c280
rq_unlock_irq kernel/sched/sched.h:1848 [inline]
__schedule+0x1477/0x1d80 kernel/sched/core.c:3518
schedule+0x8d/0x1b0 kernel/sched/core.c:3559
tty_open+0x729/0xb00 drivers/tty/tty_io.c:2036
chrdev_open+0x219/0x5c0 fs/char_dev.c:423
do_dentry_open+0x4a8/0x1160 fs/open.c:796
do_last fs/namei.c:3421 [inline]
path_openat+0x1031/0x4200 fs/namei.c:3537
do_filp_open+0x1a1/0x280 fs/namei.c:3567
do_sys_open+0x3c0/0x500 fs/open.c:1085
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45c829
Code: 0d b7 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 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f0a8477dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00000000004f8b60 RCX: 000000000045c829
RDX: 0000000000000000 RSI: 0000000020000840 RDI: ffffffffffffff9c
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000000007fe R14: 00000000004cabb1 R15: 00007f0a8477e6d4
rcu: rcu_preempt kthread starved for 10540 jiffies! g31369 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt R running task 29136 10 2 0x80000000
Call Trace:


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[syzbot]

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