syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (10499 ticks this GP) idle=27e/1/0x4000000000000002 softirq=12705/12705 fqs=0 
	(t=10500 jiffies g=6913 q=29)
rcu: rcu_preempt kthread starved for 10500 jiffies! g6913 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: RCU grace-period kthread stack dump:
rcu_preempt     R  running task    28984    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: 8512 Comm: blkid 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:ffffc900026678f0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 1ffff11012af26a1 RBX: ffff888095793508 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffea000253b040
RBP: ffffc90002667928 R08: 000000000003a728 R09: ffffed1012cf7f39
R10: ffffed1012cf7f39 R11: 0000000000000000 R12: ffff8880957935a0
R13: dffffc0000000000 R14: 1ffff11012af26b4 R15: ffff8880967bf9b8
 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]
 browse_rb mm/mmap.c:360 [inline]
 validate_mm+0x5e3/0x9b0 mm/mmap.c:420
 __vma_adjust+0x2280/0x2390 mm/mmap.c:978
 __split_vma+0x356/0x490 include/linux/mm.h:2261
 split_vma+0x7a/0xd0 mm/mmap.c:2708
 mprotect_fixup+0x6ef/0x790 mm/mprotect.c:413
 do_mprotect_pkey+0x6c2/0x8d0 mm/mprotect.c:553
 __do_sys_mprotect mm/mprotect.c:578 [inline]
 __se_sys_mprotect mm/mprotect.c:575 [inline]
 __x64_sys_mprotect+0x80/0x90 mm/mprotect.c:575
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f1f16329447
Code: 73 01 c3 48 8d 0d 5d ad 20 00 31 d2 48 29 c2 89 11 48 83 c8 ff eb eb 90 90 90 90 90 90 90 90 90 90 90 90 b8 0a 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8d 0d 2d ad 20 00 31 d2 48 29 c2 89
RSP: 002b:00007ffcfbec4878 EFLAGS: 00000206 ORIG_RAX: 000000000000000a
RAX: ffffffffffffffda RBX: 00007f1f165339d8 RCX: 00007f1f16329447
RDX: 0000000000000001 RSI: 0000000000001000 RDI: 00007f1f16532000
RBP: 00007ffcfbec4970 R08: 0000000000000001 R09: 0000000000000007
R10: 00007f1f16323a0b R11: 0000000000000206 R12: 00007f1f16313000
R13: 00007f1f16313a78 R14: 00007f1f16323a0b R15: 00007f1f16533028