INFO: rcu detected stall in do_signal (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 397a88b2 Linux 4.14.223
git tree: linux-4.14.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10ab94dad00000
kernel config: https://syzkaller.appspot.com/x/.config?x=104119cfe8dba6b3
dashboard link: https://syzkaller.appspot.com/bug?extid=06de85f9e06f7a9fed8c

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+06de85...@syzkaller.appspotmail.com

INFO: rcu_preempt detected stalls on CPUs/tasks:
(detected by 1, t=10502 jiffies, g=9886, c=9885, q=671)
All QSes seen, last rcu_preempt kthread activity 9456 (4294976685-4294967229), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor.4 R running task 29208 21213 7982 0x00000000
Call Trace:
<IRQ>
sched_show_task.cold+0x333/0x39a kernel/sched/core.c:5165
print_other_cpu_stall kernel/rcu/tree.c:1501 [inline]
check_cpu_stall kernel/rcu/tree.c:1616 [inline]
__rcu_pending kernel/rcu/tree.c:3390 [inline]
rcu_pending kernel/rcu/tree.c:3452 [inline]
rcu_check_callbacks.cold+0xd29/0xd8d kernel/rcu/tree.c:2792
update_process_times+0x29/0x60 kernel/time/timer.c:1591
tick_sched_handle+0x7d/0x150 kernel/time/tick-sched.c:165
tick_sched_timer+0x92/0x200 kernel/time/tick-sched.c:1223
__run_hrtimer kernel/time/hrtimer.c:1223 [inline]
__hrtimer_run_queues+0x30b/0xc80 kernel/time/hrtimer.c:1287
hrtimer_interrupt+0x1e6/0x5e0 kernel/time/hrtimer.c:1321
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1079 [inline]
smp_apic_timer_interrupt+0x117/0x5e0 arch/x86/kernel/apic/apic.c:1104
apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:793
</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:200
RSP: 0000:ffff8880a2507c68 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff10
RAX: 1ffffffff11e1253 RBX: 00000000004040a0 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffff88809ca4cb84
RBP: ffff8880a92b08c8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: ffff8880a92b0208 R14: ffff8880a92b0200 R15: 000000000000000b
spin_unlock_irq include/linux/spinlock.h:367 [inline]
get_signal+0x16ce/0x1ca0 kernel/signal.c:2426
do_signal+0x7c/0x1550 arch/x86/kernel/signal.c:814
exit_to_usermode_loop+0x160/0x200 arch/x86/entry/common.c:160
prepare_exit_to_usermode+0x1af/0x210 arch/x86/entry/common.c:199
retint_user+0x8/0x18
RIP: 0033:0x7ffd8e16eb4f
RSP: 002b:00007fab79dcb220 EFLAGS: 00010206
RAX: 0000000000000000 RBX: 00007ffd8e16eb4f RCX: 00000000004c086d
RDX: 0000000000057ebf RSI: 0000000000012f6c RDI: 00000000004d056a
RBP: 0000000000403bad R08: 0000000000000000 R09: 000000000000000e
R10: 001a85ffceb48cf2 R11: 0000000000000001 R12: 000000000056bf6c
R13: 00007ffd8e16eb4f R14: 00007fab79dcb300 R15: 0000000000022000
rcu_preempt kthread starved for 9456 jiffies! g9886 c9885 f0x2 RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=1
rcu_preempt R running task 30008 8 2 0x80000000
Call Trace:
context_switch kernel/sched/core.c:2808 [inline]
__schedule+0x88b/0x1de0 kernel/sched/core.c:3384
schedule+0x8d/0x1b0 kernel/sched/core.c:3428
schedule_timeout+0x4af/0xe90 kernel/time/timer.c:1747
rcu_gp_kthread+0xc0a/0x1e60 kernel/rcu/tree.c:2255
kthread+0x30d/0x420 kernel/kthread.c:232
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:404


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[syzbot]

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