INFO: rcu detected stall in do_signal (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: dcd88898 Linux 4.19.95
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10cbbb3ee00000
kernel config: https://syzkaller.appspot.com/x/.config?x=1f7fa7375205a3ab
dashboard link: https://syzkaller.appspot.com/bug?extid=a2e0b07ae7bed19cedfa
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+a2e0b0...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: (detected by 0, t=10502 jiffies, g=470681, q=30)
rcu: All QSes seen, last rcu_preempt kthread activity 10503
(4295196706-4295186203), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor.2 R running task 28944 22695 8140 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:1401 [inline]
__hrtimer_run_queues+0x33b/0xdc0 kernel/time/hrtimer.c:1463
hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1521
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 ed 73 9c 01 00 74 20 fb 66 0f 1f 44 00 00 <bf> 01 00 00 00
e8 82 f8 f2 f9 65 8b 05 cb 05 ac 78 85 c0 74 06 41
RSP: 0000:ffff88804f11fc18 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff11e4b7b RBX: 0000000000000000 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffff8880283a6afc
RBP: ffff88804f11fc20 R08: ffff8880283a6280 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888087da1448
R13: ffff888087da0d80 R14: 000000000000000a R15: 000000000000000b
spin_unlock_irq include/linux/spinlock.h:379 [inline]
get_signal+0x198e/0x1fc0 kernel/signal.c:2581
do_signal+0x95/0x1960 arch/x86/kernel/signal.c:821
exit_to_usermode_loop+0x244/0x2c0 arch/x86/entry/common.c:163
prepare_exit_to_usermode+0x293/0x2f0 arch/x86/entry/common.c:198
retint_user+0x8/0x18
RIP: 0033:0x4057e9
Code: d0 ff ff ff 01 48 8b 7c 24 28 c7 44 24 34 00 00 00 00 e8 7a d9 01 00
85 c0 75 23 48 6b 44 24 20 18 8b 7c 24 1c 48 03 44 24 38 <48> 8b 48 10 48
8b 50 08 48 8b 30 e8 17 f5 00 00 89 44 24 34 64 f0
RSP: 002b:00007fa603a7ca70 EFLAGS: 00010206
RAX: 0000000022b4b118 RBX: 0000000000000007 RCX: 0000000000414d47
RDX: 8df4064c8803b078 RSI: 0000000000000000 RDI: 0000000000000007
RBP: 000000000075c1c0 R08: 00007fa603a7ca70 R09: 000000000075c1c0
R10: 0000000000000000 R11: 0000000000000000 R12: 00007fa603a7d6d4
R13: 00000000004cbf38 R14: 00000000004e6c10 R15: 00000000ffffffff
rcu: rcu_preempt kthread starved for 10533 jiffies! g470681 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.