syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-...!: (10499 ticks this GP) idle=a0e/1/0x4000000000000002 softirq=10209/10209 fqs=0 
	(t=10501 jiffies g=6077 q=40)
rcu: rcu_preempt kthread starved for 10502 jiffies! g6077 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt     I29032    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: 8090 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:1514 [inline]
 __hrtimer_run_queues+0x403/0x840 kernel/time/hrtimer.c:1576
 hrtimer_interrupt+0x38c/0xda0 kernel/time/hrtimer.c:1638
 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+0x219/0x2e0 mm/memcontrol.c:2925
Code: 4b 0d 89 e8 59 97 00 00 bf 01 00 00 00 e8 2f e3 9b ff 65 8b 05 d4 fd 4a 7e 85 c0 74 53 48 83 c4 08 5b 41 5c 41 5d 41 5e 41 5f <5d> c3 49 8d 5f 10 48 89 df be 08 00 00 00 e8 04 c1 fa ff 48 8b 45
RSP: 0018:ffffc900020075e8 EFLAGS: 00000296 ORIG_RAX: ffffffffffffff13
RAX: 0000000000000001 RBX: ffffea0002314b00 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffea0002314b00
RBP: ffffc900020075e8 R08: dffffc0000000000 R09: fffffbfff12877ed
R10: fffffbfff12877ed R11: 0000000000000000 R12: ffff888094f84120
R13: dffffc0000000000 R14: 1ffff110129f0824 R15: ffff88809f18b468
 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_irq+0xc1/0x140 kernel/sched/core.c:4338
 retint_kernel+0x1b/0x2b
RIP: 0010:arch_local_save_flags arch/x86/include/asm/paravirt.h:747 [inline]
RIP: 0010:arch_local_irq_save arch/x86/include/asm/paravirt.h:769 [inline]
RIP: 0010:lock_is_held_type+0x60/0x2b0 kernel/locking/lockdep.c:4518
Code: c1 ef 03 43 8a 04 37 84 c0 0f 85 60 01 00 00 41 83 7d 00 00 0f 85 79 01 00 00 48 c7 c0 20 96 0a 89 48 c1 e8 03 42 80 3c 30 00 <74> 0c 48 c7 c7 20 96 0a 89 e8 c2 56 56 00 48 83 3d da d9 ae 07 00
RSP: 0018:ffffc90002007840 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff02
RAX: 1ffffffff12152c4 RBX: ffff88809859e4c0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 00000000ffffffff RDI: ffffffff890d4be0
RBP: ffffc90002007890 R08: ffffffff81e34cb2 R09: 0000000000000000
R10: fffffbfff12877ed R11: 0000000000000000 R12: 0000000000000000
R13: ffff88809859ed54 R14: dffffc0000000000 R15: 1ffff110130b3daa
 lock_is_held include/linux/lockdep.h:361 [inline]
 ___might_sleep+0x3e/0x5e0 kernel/sched/core.c:6765
 __might_sleep+0x8f/0x100 kernel/sched/core.c:6753
 __mutex_lock_common+0x4f/0x2e10 kernel/locking/mutex.c:938
 __mutex_lock kernel/locking/mutex.c:1106 [inline]
 mutex_lock_nested+0x1b/0x30 kernel/locking/mutex.c:1121
 kernfs_iop_permission+0x62/0xa0 fs/kernfs/inode.c:282
 do_inode_permission fs/namei.c:384 [inline]
 inode_permission+0x276/0x520 fs/namei.c:449
 may_lookup fs/namei.c:1698 [inline]
 link_path_walk+0x200/0x1410 fs/namei.c:2078
 path_lookupat+0x69/0xb30 fs/namei.c:2311
 filename_lookup+0x1d4/0x690 fs/namei.c:2342
 user_path_at_empty+0x40/0x50 fs/namei.c:2602
 user_path_at include/linux/namei.h:49 [inline]
 vfs_statx+0xbb/0x190 fs/stat.c:187
 vfs_fstatat include/linux/fs.h:3260 [inline]
 __do_sys_newfstatat fs/stat.c:368 [inline]
 __se_sys_newfstatat fs/stat.c:362 [inline]
 __x64_sys_newfstatat+0xbd/0x120 fs/stat.c:362
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7f790e52fe1a
Code: 83 c8 ff c3 90 90 90 90 90 90 90 90 90 90 90 90 83 ff 01 89 f0 48 89 d6 77 1e 48 63 f8 4d 63 d0 48 89 ca b8 06 01 00 00 0f 05 <48> 3d 00 f0 ff ff 77 1a f3 c3 0f 1f 40 00 48 8b 05 e9 4f 2b 00 64
RSP: 002b:00007ffe302b8218 EFLAGS: 00000246 ORIG_RAX: 0000000000000106
RAX: ffffffffffffffda RBX: 00007ffe302b82f0 RCX: 00007f790e52fe1a
RDX: 00007ffe302b8250 RSI: 00007f790e806e96 RDI: 0000000000000004
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f790e806e96
R13: 00007ffe302b8250 R14: 00007f790ea11820 R15: 00007f790e8072a2