INFO: rcu detected stall in force_sig_fault

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: fb279f4e Merge branch 'i2c/for-current-fixed' of git://git..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=127489fde00000
kernel config: https://syzkaller.appspot.com/x/.config?x=8b13b05f0e61d957
dashboard link: https://syzkaller.appspot.com/bug?extid=d2d2cc398a180b2255d0
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
CC: [chri...@brauner.io ebie...@xmission.com gu...@fb.com linux-...@vger.kernel.org ol...@redhat.com]

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+d2d2cc...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
(detected by 1, t=10502 jiffies, g=8125, q=1010)
rcu: All QSes seen, last rcu_preempt kthread activity 10444 (4294967725-4294957281), jiffies_till_next_fqs=1, root ->qsmask 0x0
syz-executor.5 R running task 28352 8727 8573 0x80000004
Call Trace:
<IRQ>
sched_show_task+0x408/0x560 kernel/sched/core.c:5952
print_other_cpu_stall kernel/rcu/tree_stall.h:430 [inline]
check_cpu_stall kernel/rcu/tree_stall.h:558 [inline]
rcu_pending kernel/rcu/tree.c:3030 [inline]
rcu_sched_clock_irq+0x147c/0x1970 kernel/rcu/tree.c:2276
update_process_times+0x12c/0x180 kernel/time/timer.c:1726
tick_sched_handle kernel/time/tick-sched.c:171 [inline]
tick_sched_timer+0x254/0x410 kernel/time/tick-sched.c:1314
__run_hrtimer kernel/time/hrtimer.c:1517 [inline]
__hrtimer_run_queues+0x3cf/0x7d0 kernel/time/hrtimer.c:1579
hrtimer_interrupt+0x373/0xd60 kernel/time/hrtimer.c:1641
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1119 [inline]
smp_apic_timer_interrupt+0x109/0x280 arch/x86/kernel/apic/apic.c:1144
apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
</IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:752 [inline]
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa5/0xd0 kernel/locking/spinlock.c:191
Code: b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 0c 48 c7 c7 50 d3 0a 89 e8 fa 85 b5 f9 48 83 3d f2 78 0f 01 00 74 2c 4c 89 f7 57 9d <0f> 1f 44 00 00 bf 01 00 00 00 e8 dc 32 56 f9 65 8b 05 51 c3 06 78
RSP: 0000:ffffc90001607e60 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff1215a6a RBX: ffff88803ff1b2c0 RCX: dffffc0000000000
RDX: dffffc0000000000 RSI: 000000000003ffff RDI: 0000000000000282
RBP: ffffc90001607ee8 R08: ffffffff817a3680 R09: ffffed1007fe3659
R10: ffffed1007fe3659 R11: 0000000000000000 R12: ffff8880567c02c0
R13: ffff8880567c09e0 R14: 0000000000000282 R15: ffff88803ff1b488
spin_unlock_irqrestore include/linux/spinlock.h:393 [inline]
force_sig_info_to_task+0x272/0x2e0 kernel/signal.c:1334
force_sig_fault_to_task kernel/signal.c:1676 [inline]
force_sig_fault+0xbb/0x130 kernel/signal.c:1683
page_fault+0x39/0x40 arch/x86/entry/entry_64.S:1203
RIP: 0033:0x4044f9
Code: d0 ff ff ff 01 48 8b 7c 24 20 c7 44 24 2c 00 00 00 00 e8 ca 01 02 00 85 c0 75 23 48 6b 44 24 18 18 8b 7c 24 28 48 03 44 24 30 <48> 8b 48 10 48 8b 50 08 48 8b 30 e8 67 1d 01 00 89 44 24 2c 64 f0
RSP: 002b:00007f669e0999e0 EFLAGS: 00010202
RAX: 0000000027b21b68 RBX: 00007f669e09a6d4 RCX: 00000000004162a7
RDX: 1e225e2db78186d0 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 000000000076bf20 R08: 00007f669e0999e0 R09: 000000000076bf20
R10: 0000000000000000 R11: 0000000000000000 R12: 00000000ffffffff
R13: 0000000000000c1c R14: 00000000004c13cb R15: 000000000076bf2c
rcu: rcu_preempt kthread starved for 10444 jiffies! g8125 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: RCU grace-period kthread stack dump:
rcu_preempt R running task 29072 10 2 0x80004000
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.