syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-....: (10499 ticks this GP) idle=452/1/0x4000000000000002 softirq=11906/11906 fqs=2768 
	(t=10501 jiffies g=6521 q=760)
rcu: rcu_preempt kthread starved for 4965 jiffies! g6521 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: 8546 Comm: syz-executor.1 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+0x14c/0x590 kernel/fork.c:280
Code: 2e 00 48 89 df 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
RSP: 0018:ffffc90002177a90 EFLAGS: 00000a06 ORIG_RAX: ffffffffffffff13
RAX: 1ffff11013e207b1 RBX: ffff88809f103d88 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffea00029d5c00
RBP: ffffc90002177ac8 R08: 000000000003a728 R09: fffffbfff124248a
R10: fffffbfff124248a R11: 0000000000000000 R12: ffff88809f103e20
R13: dffffc0000000000 R14: 1ffff11013e207c4 R15: ffff8880a1d97738
 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 include/linux/spinlock_api_smp.h:152 [inline]
 _raw_spin_unlock+0x3a/0x40 kernel/locking/spinlock.c:183
 spin_unlock include/linux/spinlock.h:378 [inline]
 do_fault_around mm/memory.c:3614 [inline]
 do_read_fault+0x4d6/0x9e0 mm/memory.c:3632
 do_fault mm/memory.c:3766 [inline]
 handle_pte_fault mm/memory.c:3997 [inline]
 __handle_mm_fault mm/memory.c:4127 [inline]
 handle_mm_fault+0x1bb8/0x2890 mm/memory.c:4164
 do_user_addr_fault+0x589/0xaf0 arch/x86/mm/fault.c:1441
 __do_page_fault+0xd3/0x1f0 arch/x86/mm/fault.c:1506
 do_page_fault+0x99/0xb0 arch/x86/mm/fault.c:1530
 page_fault+0x39/0x40 arch/x86/entry/entry_64.S:1203
RIP: 0033:0x443583
Code: 00 00 00 00 00 66 90 66 0f 6e ce 89 f8 25 ff 0f 00 00 66 0f 60 c9 3d c0 0f 00 00 66 0f 61 c9 66 0f 70 c9 00 0f 8f 4d 01 00 00 <f3> 0f 6f 07 66 0f ef db 66 0f 6f e0 66 0f 74 c1 66 0f 74 e3 66 0f
RSP: 002b:00007ffd53854db8 EFLAGS: 00010283
RAX: 00000000000008fd RBX: 00007ffd53855320 RCX: 00000000fbad8001
RDX: 00007ffd53855498 RSI: 0000000000000025 RDI: 00000000004c08fd
RBP: 00007ffd53855310 R08: 0000000000000000 R09: 00007ffd53855498
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004c08fd
R13: 00007ffd53855498 R14: 00007ffd53855498 R15: 0000000000000000