syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-...!: (1 GPs behind) idle=922/1/0x4000000000000002 softirq=11850/11851 fqs=4 
	(t=10500 jiffies g=6709 q=307)
rcu: rcu_preempt kthread starved for 10491 jiffies! g6709 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt     R  running task    28864    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: 8433 Comm: syz-executor.0 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:ffffc90001e97698 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 1ffff11012e258d1 RBX: ffff88809712c688 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffea00025afe00
RBP: ffffc90001e976d0 R08: dffffc0000000000 R09: fffffbfff124248a
R10: fffffbfff124248a R11: 0000000000000000 R12: ffff88809712c720
R13: dffffc0000000000 R14: 1ffff11012e258e4 R15: ffff8880905af9f8
 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_irq+0xc1/0x140 kernel/sched/core.c:4338
 retint_kernel+0x1b/0x2b
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:752 [inline]
RIP: 0010:lock_acquire+0x1b2/0x250 kernel/locking/lockdep.c:4488
Code: c1 e8 03 42 80 3c 30 00 74 0c 48 c7 c7 68 95 2a 89 e8 02 7a 57 00 48 83 3d 92 e8 ce 07 00 0f 84 9c 00 00 00 48 8b 7d c0 57 9d <0f> 1f 44 00 00 48 83 c4 30 5b 41 5c 41 5d 41 5e 41 5f 5d c3 44 89
RSP: 0018:ffffc90001e978e0 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff12552ad RBX: 0000000000000000 RCX: ffffffff815c85d0
RDX: dffffc0000000000 RSI: 0000000000000004 RDI: 0000000000000286
RBP: ffffc90001e97938 R08: dffffc0000000000 R09: fffffbfff138ab19
R10: fffffbfff138ab19 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000000000 R14: dffffc0000000000 R15: ffffffff892fe990
 __fs_reclaim_acquire+0x24/0x30 mm/page_alloc.c:4084
 fs_reclaim_acquire+0x5f/0xd0 mm/page_alloc.c:4095
 slab_pre_alloc_hook mm/slab.h:562 [inline]
 slab_alloc mm/slab.c:3306 [inline]
 kmem_cache_alloc_trace+0x31/0x2f0 mm/slab.c:3549
 kmalloc include/linux/slab.h:556 [inline]
 kzalloc include/linux/slab.h:670 [inline]
 kernfs_fop_open+0x3a9/0xc20 fs/kernfs/file.c:647
 do_dentry_open+0x740/0x10c0 fs/open.c:797
 vfs_open+0x73/0x80 fs/open.c:914
 do_last fs/namei.c:3420 [inline]
 path_openat+0x1387/0x4240 fs/namei.c:3537
 do_filp_open+0x192/0x3d0 fs/namei.c:3567
 do_sys_open+0x29f/0x560 fs/open.c:1097
 __do_sys_open fs/open.c:1115 [inline]
 __se_sys_open fs/open.c:1110 [inline]
 __x64_sys_open+0x87/0x90 fs/open.c:1110
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x414cc0
Code: 05 48 3d 01 f0 ff ff 0f 83 2d 19 00 00 c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 83 3d ad 37 66 00 00 75 14 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 04 19 00 00 c3 48 83 ec 08 e8 0a fa ff ff
RSP: 002b:00007ffe7d43d338 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007ffe7d43d362 RCX: 0000000000414cc0
RDX: 00007ffe7d43d366 RSI: 0000000000080001 RDI: 00007ffe7d43d8d0
RBP: 00007ffe7d43d360 R08: 0000000000000000 R09: 0000000000000002
R10: 0000000000000017 R11: 0000000000000246 R12: 00007ffe7d43d8d0
R13: 00007ffe7d43dcb8 R14: 0000000000000000 R15: 00007ffe7d43d890