INFO: rcu detected stall in chrdev_open

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: c7ecf3e3 Linux 4.19.92
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=15858971e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=f1b833aa58e7216b
dashboard link: https://syzkaller.appspot.com/bug?extid=811771edb3c20aaa1c86
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+811771...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: (detected by 0, t=10502 jiffies, g=273229, q=31)
rcu: All QSes seen, last rcu_preempt kthread activity 10502
(4295085511-4295075009), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor.0 R running task 26784 5439 7743 0x00000000
Call Trace:
<IRQ>
sched_show_task kernel/sched/core.c:5338 [inline]
sched_show_task.cold+0x2ee/0x35d 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+0xaa1/0xd90 kernel/rcu/tree.c:2682
update_process_times+0x32/0x80 kernel/time/timer.c:1638
tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:164
tick_sched_timer+0x47/0x130 kernel/time/tick-sched.c:1274
__run_hrtimer kernel/time/hrtimer.c:1398 [inline]
__hrtimer_run_queues+0x33b/0xdc0 kernel/time/hrtimer.c:1460
hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1518
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1067 [inline]
smp_apic_timer_interrupt+0x111/0x550 arch/x86/kernel/apic/apic.c:1092
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:893
</IRQ>
RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169
[inline]
RIP: 0010:_raw_spin_unlock_irq+0x54/0x90 kernel/locking/spinlock.c:192
Code: c0 d8 5b f2 88 48 ba 00 00 00 00 00 fc ff df 48 c1 e8 03 80 3c 10 00
75 33 48 83 3d 4d ff a5 01 00 74 20 fb 66 0f 1f 44 00 00 <bf> 01 00 00 00
e8 22 b4 fc f9 65 8b 05 2b 91 b5 78 85 c0 74 06 41
RSP: 0018:ffff88809fab7718 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff11e4b7b RBX: ffff888095934b60 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffff888095934dbc
RBP: ffff88809fab7720 R08: ffff888095934540 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880ae82c240
R13: ffffffff87aa96a0 R14: ffff888095934540 R15: ffff8880ae82c240
rq_unlock_irq kernel/sched/sched.h:1842 [inline]
__schedule+0x1495/0x1dc0 kernel/sched/core.c:3518
schedule+0x92/0x1c0 kernel/sched/core.c:3559
tty_open+0x765/0xb70 drivers/tty/tty_io.c:2036
chrdev_open+0x245/0x6b0 fs/char_dev.c:423
do_dentry_open+0x4c3/0x1210 fs/open.c:796
vfs_open+0xa0/0xd0 fs/open.c:905
do_last fs/namei.c:3418 [inline]
path_openat+0x10d7/0x45e0 fs/namei.c:3534
do_filp_open+0x1a1/0x280 fs/namei.c:3564
do_sys_open+0x3fe/0x550 fs/open.c:1088
__do_sys_openat fs/open.c:1115 [inline]
__se_sys_openat fs/open.c:1109 [inline]
__x64_sys_openat+0x9d/0x100 fs/open.c:1109
do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a9e9
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:00007f6a76257c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 000000000045a9e9
RDX: 0000000000000000 RSI: 0000000020000240 RDI: ffffffffffffff9c
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6a762586d4
R13: 00000000004c87ee R14: 00000000004e0018 R15: 00000000ffffffff
rcu: rcu_preempt kthread starved for 10502 jiffies! g273229 f0x2
RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt R running task 29104 10 2 0x80000000
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+0x4db/0xfc0 kernel/time/timer.c:1806
rcu_gp_kthread+0xd5c/0x2190 kernel/rcu/tree.c:2202
kthread+0x354/0x420 kernel/kthread.c:246
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415


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[syzbot]

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