INFO: rcu detected stall in sys_poll (2)

[syzbot <syzbot+c3ed57cd8f699826dd95@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    ae608821 Merge tag 'trace-v5.5-rc5' of git://git.kernel.or..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=157edeb9e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=db5ff86cbb23b415
dashboard link: https://syzkaller.appspot.com/bug?extid=c3ed57cd8f699826dd95
compiler:       clang version 9.0.0 (/home/glider/llvm/clang  
80fee25776c2fb61e74c1ecb1a523375c2500b69)

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+c3ed57cd8f699826dd95@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-...!: (1 GPs behind) idle=5da/1/0x4000000000000002  
softirq=13907/13908 fqs=38
	(t=10501 jiffies g=6889 q=136)
rcu: rcu_preempt kthread starved for 10426 jiffies! g6889 f0x0  
RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
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 0
CPU: 0 PID: 8477 Comm: udevd Not tainted 5.5.0-rc5-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+0x151/0x590 kernel/fork.c:280
Code: 31 f6 e8 02 8d 6f 00 43 80 3c 2e 00 74 08 4c 89 e7 e8 73 94 6a 00 49  
8b 1c 24 48 83 c3 08 48 89 d8 48 c1 e8 03 42 80 3c 28 00 <74> 08 48 89 df  
e8 55 94 6a 00 48 8b 3b be fc ff ff ff e8 28 04 00
RSP: 0018:ffffc90001e57760 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 1ffff11013e8ed61 RBX: ffff88809f476b08 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffea0002a59a40
RBP: ffffc90001e57798 R08: 000000000003a728 R09: ffffed10125b3711
R10: ffffed10125b3711 R11: 0000000000000000 R12: ffff88809f476a20
R13: dffffc0000000000 R14: 1ffff11013e8ed44 R15: ffff888092d9b878
  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
  schedule+0x181/0x210 kernel/sched/core.c:4155
  schedule_hrtimeout_range_clock+0x3c7/0x510 kernel/time/hrtimer.c:2130
  schedule_hrtimeout_range+0x2a/0x40 kernel/time/hrtimer.c:2175
  poll_schedule_timeout+0x11c/0x1c0 fs/select.c:243
  do_poll fs/select.c:951 [inline]
  do_sys_poll+0x83f/0x1250 fs/select.c:1001
  __do_sys_poll fs/select.c:1059 [inline]
  __se_sys_poll+0x1b0/0x360 fs/select.c:1047
  __x64_sys_poll+0x7b/0x90 fs/select.c:1047
  do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7fe82049b678
Code: 11 48 83 c8 ff eb ea 90 90 90 90 90 90 90 90 90 90 90 48 83 ec 28 8b  
05 82 8f 2b 00 85 c0 75 17 48 63 d2 b8 07 00 00 00 0f 05 <48> 3d 00 f0 ff  
ff 77 51 48 83 c4 28 c3 89 54 24 08 48 89 74 24 10
RSP: 002b:00007fffd9dcc090 EFLAGS: 00000246 ORIG_RAX: 0000000000000007
RAX: ffffffffffffffda RBX: 20c49ba5e353f7cf RCX: 00007fe82049b678
RDX: 000000000000ee2a RSI: 0000000000000001 RDI: 00007fffd9dcc150
RBP: 0000000000000000 R08: 00007fffd9dcc0a0 R09: 00007fffd9de50b8
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000150dc00
R13: 000000000000214d R14: 00007fffd9dcc124 R15: 0000000001509250


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