INFO: rcu detected stall in rtc_handle_legacy_irq

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 7daf201d7fe8 Linux 4.18-rc2
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15200728400000
kernel config: https://syzkaller.appspot.com/x/.config?x=a63be0c83e84d370
dashboard link: https://syzkaller.appspot.com/bug?extid=5e6605c3e98012705d2e
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [a.z...@towertech.it alexandr...@bootlin.com
linux-...@vger.kernel.org linu...@vger.kernel.org]

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+5e6605...@syzkaller.appspotmail.com

INFO: rcu_sched self-detected stall on CPU
1-....: (1 GPs behind) idle=ec2/1/4611686018427387906 softirq=24778/24779
fqs=31206
(t=125000 jiffies g=14068 c=14067 q=1861)
NMI backtrace for cpu 1
CPU: 1 PID: 19 Comm: kworker/1:0 Not tainted 4.18.0-rc2+ #116
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: events rtc_timer_do_work
Call Trace:
<IRQ>
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1c9/0x2b4 lib/dump_stack.c:113
nmi_cpu_backtrace.cold.4+0x19/0xce lib/nmi_backtrace.c:103
nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_single_cpu_backtrace include/linux/nmi.h:156 [inline]
rcu_dump_cpu_stacks+0x175/0x1c2 kernel/rcu/tree.c:1336
print_cpu_stall kernel/rcu/tree.c:1485 [inline]
check_cpu_stall.isra.60.cold.78+0x36c/0x5a6 kernel/rcu/tree.c:1553
__rcu_pending kernel/rcu/tree.c:3244 [inline]
rcu_pending kernel/rcu/tree.c:3291 [inline]
rcu_check_callbacks+0x23f/0xcd0 kernel/rcu/tree.c:2646
update_process_times+0x2d/0x70 kernel/time/timer.c:1636
tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164
tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
__run_hrtimer kernel/time/hrtimer.c:1398 [inline]
__hrtimer_run_queues+0x3eb/0x10c0 kernel/time/hrtimer.c:1460
hrtimer_interrupt+0x2f3/0x750 kernel/time/hrtimer.c:1518
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
smp_apic_timer_interrupt+0x165/0x730 arch/x86/kernel/apic/apic.c:1050
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
</IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:783
[inline]
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160
[inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa1/0xc0
kernel/locking/spinlock.c:184
Code: a8 b0 f1 88 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c
02 00 75 21 48 83 3d 8e 58 5f 01 00 74 0e 48 89 df 57 9d <0f> 1f 44 00 00
eb bb 0f 0b 0f 0b e8 ff 87 27 fa eb 97 e8 f8 87 27
RSP: 0000:ffff8801d9b37308 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
RAX: dffffc0000000000 RBX: 0000000000000282 RCX: 1ffff1003b3655b5
RDX: 1ffffffff11e3615 RSI: 0000000000000000 RDI: 0000000000000282
RBP: ffff8801d9b37318 R08: ffff8801d9b2ad38 R09: 0000000000000006
R10: ffff8801d9b2a500 R11: 0000000000000000 R12: ffff8801cdfd4788
R13: ffff8801cdfd4818 R14: ffff8801cdfd4788 R15: ffffffff8557be80
spin_unlock_irqrestore include/linux/spinlock.h:365 [inline]
rtc_handle_legacy_irq+0x81/0x190 drivers/rtc/interface.c:606
rtc_uie_update_irq+0x1f/0x30 drivers/rtc/interface.c:641
rtc_timer_do_work+0x283/0x1200 drivers/rtc/interface.c:981
process_one_work+0xc73/0x1ba0 kernel/workqueue.c:2153
worker_thread+0x189/0x13c0 kernel/workqueue.c:2296
kthread+0x345/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412


---
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#bug-status-tracking for how to communicate with
syzbot.

[syzbot]

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