syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (10499 ticks this GP) idle=e1a/1/0x4000000000000002 softirq=12984/12984 fqs=44 
	(t=10501 jiffies g=6673 q=200)
rcu: rcu_preempt kthread starved for 10413 jiffies! g6673 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: 8598 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:ffffc900023876d8 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 1ffff110133c0671 RBX: ffff888099e03388 RCX: 0000000000000000
RDX: ffffc90001e29000 RSI: 0000000000000000 RDI: ffffea0002556a40
RBP: ffffc90002387710 R08: 000000000003a728 R09: ffffed1012666ed9
R10: ffffed1012666ed9 R11: 0000000000000000 R12: ffff888099e03420
R13: dffffc0000000000 R14: 1ffff110133c0684 R15: ffff8880933376b8
 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:__find_get_block+0x235/0xb10 fs/buffer.c:1334
Code: fc ff df 80 3c 08 00 74 0c 48 c7 c7 78 95 2a 89 e8 40 9e e7 ff 48 83 3d e0 0c 5f 07 00 0f 84 b3 08 00 00 fb 66 0f 1f 44 00 00 <48> 85 db 74 43 e8 d1 35 ab ff 48 89 df e8 19 d7 ff ff 49 89 de 48
RSP: 0018:ffffc90002387920 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff02
RAX: 1ffffffff12552af RBX: ffff8880962007e0 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffff888069b5c884
RBP: ffffc90002387968 R08: ffff888069b5c898 R09: fffffbfff140cf2e
R10: fffffbfff140cf2e R11: 0000000000000000 R12: 00000000000341b8
R13: 0000000000000009 R14: 0000000000001000 R15: 0000000000000000
 __getblk_gfp+0x2f/0x2a0 fs/buffer.c:1358
 sb_getblk include/linux/buffer_head.h:325 [inline]
 ext4_getblk+0x162/0x460 fs/ext4/inode.c:834
 ext4_bread+0x4a/0x340 fs/ext4/inode.c:877
 __ext4_read_dirblock+0x36/0xd90 fs/ext4/namei.c:112
 ext4_add_entry+0x2455/0x3db0 fs/ext4/namei.c:2216
 ext4_mkdir+0xd03/0x1460 fs/ext4/namei.c:2791
 vfs_mkdir+0x43f/0x610 fs/namei.c:3819
 do_mkdirat+0x1d7/0x320 fs/namei.c:3842
 __do_sys_mkdir fs/namei.c:3858 [inline]
 __se_sys_mkdir fs/namei.c:3856 [inline]
 __x64_sys_mkdir+0x60/0x70 fs/namei.c:3856
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45af49
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f22a3844c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 000000000045af49
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000020000180
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f22a38456d4
R13: 00000000004c09b2 R14: 00000000004e03f0 R15: 00000000ffffffff