syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (1 GPs behind) idle=306/1/0x4000000000000002 softirq=10491/10494 fqs=37 
	(t=10500 jiffies g=6297 q=396)
rcu: rcu_preempt kthread starved for 10422 jiffies! g6297 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: RCU grace-period kthread stack dump:
rcu_preempt     R  running task    29032    10      2 0x80004000
Call Trace:
 context_switch kernel/sched/core.c:3385 [inline]
 __schedule+0x9a0/0xcc0 kernel/sched/core.c:4081
 schedule+0x181/0x210 kernel/sched/core.c:4155
 schedule_timeout+0x14f/0x240 kernel/time/timer.c:1895
 rcu_gp_fqs_loop kernel/rcu/tree.c:1661 [inline]
 rcu_gp_kthread+0xed8/0x1770 kernel/rcu/tree.c:1821
 kthread+0x332/0x350 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
NMI backtrace for cpu 1
CPU: 1 PID: 8139 Comm: udevd Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1fb/0x318 lib/dump_stack.c:118
 nmi_cpu_backtrace+0xaf/0x1a0 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x174/0x290 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x10/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x15a/0x220 kernel/rcu/tree_stall.h:254
 print_cpu_stall kernel/rcu/tree_stall.h:455 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:529 [inline]
 rcu_pending kernel/rcu/tree.c:2827 [inline]
 rcu_sched_clock_irq+0xe25/0x1ad0 kernel/rcu/tree.c:2271
 update_process_times+0x12d/0x180 kernel/time/timer.c:1726
 tick_sched_handle kernel/time/tick-sched.c:167 [inline]
 tick_sched_timer+0x263/0x420 kernel/time/tick-sched.c:1310
 __run_hrtimer kernel/time/hrtimer.c:1517 [inline]
 __hrtimer_run_queues+0x403/0x840 kernel/time/hrtimer.c:1579
 hrtimer_interrupt+0x38c/0xda0 kernel/time/hrtimer.c:1641
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline]
 smp_apic_timer_interrupt+0x109/0x280 arch/x86/kernel/apic/apic.c:1135
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
 </IRQ>
RIP: 0010:free_thread_stack+0x16d/0x590 kernel/fork.c:284
Code: c3 08 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 25 a0 69 00 48 8b 3b be fc ff ff ff e8 28 04 00 00 43 80 3c 2e 00 <74> 08 4c 89 e7 e8 09 a0 69 00 49 8b 1c 24 48 83 c3 08 48 89 d8 48
RSP: 0018:ffffc90001ee7ab0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: ffffffff81487433 RBX: ffff88808c685d08 RCX: ffff8880a44d4080
RDX: 0000000000000000 RSI: 00000000fffffffc RDI: ffffea000291a100
RBP: ffffc90001ee7ae8 R08: dffffc0000000000 R09: fffffbfff120248a
R10: fffffbfff120248a R11: 0000000000000000 R12: ffff88808c685da0
R13: dffffc0000000000 R14: 1ffff110118d0bb4 R15: ffff888093b53828
 release_task_stack kernel/fork.c:440 [inline]
 put_task_stack+0xa3/0x130 kernel/fork.c:451
 finish_task_switch+0x3f1/0x550 kernel/sched/core.c:3256
 context_switch kernel/sched/core.c:3388 [inline]
 __schedule+0x9a8/0xcc0 kernel/sched/core.c:4081
 preempt_schedule_common kernel/sched/core.c:4236 [inline]
 preempt_schedule+0xdb/0x120 kernel/sched/core.c:4261
 ___preempt_schedule+0x16/0x18 arch/x86/entry/thunk_64.S:50
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
 _raw_spin_unlock_irqrestore+0xcc/0xe0 kernel/locking/spinlock.c:191
 spin_unlock_irqrestore include/linux/spinlock.h:393 [inline]
 __wake_up_common_lock kernel/sched/wait.c:125 [inline]
 __wake_up+0xe1/0x150 kernel/sched/wait.c:142
 fsnotify_add_event+0x2fc/0x390 fs/notify/notification.c:126
 inotify_handle_event+0x409/0x620 fs/notify/inotify/inotify_fsnotify.c:129
 inotify_ignored_and_remove_idr+0x95/0x110 fs/notify/inotify/inotify_user.c:493
 inotify_freeing_mark+0x1d/0x30 fs/notify/inotify/inotify_fsnotify.c:143
 fsnotify_free_mark fs/notify/mark.c:423 [inline]
 fsnotify_destroy_mark+0x131/0x190 fs/notify/mark.c:432
 __do_sys_inotify_rm_watch fs/notify/inotify/inotify_user.c:787 [inline]
 __se_sys_inotify_rm_watch+0x165/0x230 fs/notify/inotify/inotify_user.c:762
 __x64_sys_inotify_rm_watch+0x5b/0x70 fs/notify/inotify/inotify_user.c:762
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f55b85aea97
Code: 73 01 c3 48 8b 0d a1 83 2a 00 31 d2 48 29 c2 64 89 11 48 83 c8 ff eb ea 90 90 90 90 90 90 90 90 90 90 90 b8 ff 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 71 83 2a 00 31 d2 48 29 c2 64
RSP: 002b:00007fff39094038 EFLAGS: 00000293 ORIG_RAX: 00000000000000ff
RAX: ffffffffffffffda RBX: 0000000001232520 RCX: 00007f55b85aea97
RDX: 0000000000000007 RSI: 0000000000000020 RDI: 0000000000000006
RBP: 0000000001219250 R08: 00007f55b8e9a7a0 R09: 0000000000000000
R10: 000000000121b8c0 R11: 0000000000000293 R12: 0000000000000020
R13: 0000000000625500 R14: 0000000001219250 R15: 000000000000000b