syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (10500 ticks this GP) idle=dc2/1/0x4000000000000002 softirq=12260/12260 fqs=37 
	(t=10500 jiffies g=6517 q=148)
rcu: rcu_preempt kthread starved for 10424 jiffies! g6517 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: RCU grace-period kthread stack dump:
rcu_preempt     R  running task    28992    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: 8299 Comm: blkid 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:__memcg_kmem_uncharge+0x6/0x1a0 mm/memcontrol.c:2909
Code: f1 8c 07 00 74 12 48 81 c3 08 02 00 00 48 89 df 4c 89 f6 e8 7c 87 ff ff 5b 41 5e 5d c3 0f 1f 80 00 00 00 00 55 48 89 e5 41 57 <41> 56 41 55 41 54 53 50 89 f3 49 89 fc 48 b8 00 00 00 00 00 fc ff
RSP: 0018:ffffc90001f47a78 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: ffffffff81486ea4 RBX: ffffea0002a4ba40 RCX: ffff8880a9a96200
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffea0002a4ba40
RBP: ffffc90001f47a80 R08: 000000000003a728 R09: ffffed10120e3eb7
R10: ffffed10120e3eb7 R11: 0000000000000000 R12: ffff8880a926fda0
R13: dffffc0000000000 R14: 1ffff1101524dfb4 R15: ffff88809071f5a8
 memcg_kmem_uncharge include/linux/memcontrol.h:1402 [inline]
 free_thread_stack+0x12e/0x590 kernel/fork.c:284
 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:3562 [inline]
 do_read_fault+0x4d6/0x9e0 mm/memory.c:3580
 do_fault mm/memory.c:3714 [inline]
 handle_pte_fault mm/memory.c:3945 [inline]
 __handle_mm_fault mm/memory.c:4075 [inline]
 handle_mm_fault+0x1bb8/0x2890 mm/memory.c:4112
 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: 0033:0x7f2f1aeda900
Code: ff 48 8d 3a 48 81 ec 80 00 00 00 e8 8a d4 03 00 48 81 c4 80 00 00 00 e9 73 ff ff ff 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <b8> 3f 00 00 00 0f 05 48 3d 01 f0 ff ff 73 01 c3 48 8b 0d 01 95 2d
RSP: 002b:00007ffca3df54d8 EFLAGS: 00010206
RAX: 00000000ffffffff RBX: 0000000000000003 RCX: 0000000000002000
RDX: 0000000000006000 RSI: 0000000000e98040 RDI: 00007ffca3df54f0
RBP: 0000000000e98040 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 00007f2f1aeda900 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000003 R15: 0000000000000005