syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P3623/1:b..l
	(detected by 0, t=10502 jiffies, g=123757, q=77 ncpus=2)
task:udevd           state:R  running task     stack:23040 pid:3623  ppid:1      flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5244 [inline]
 __schedule+0x10e9/0x40d0 kernel/sched/core.c:6561
 preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6873
 irqentry_exit+0x63/0x70 kernel/entry/common.c:439
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:lock_acquire+0x20f/0x490 kernel/locking/lockdep.c:5666
Code: 00 9c 8f 84 24 80 00 00 00 f6 84 24 81 00 00 00 02 0f 85 f5 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 44 3d 00 00 00 00 00 66 43 c7 44 3d 09 00 00 43 c6 44 3d 0b
RSP: 0018:ffffc90003257820 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ed451cf5aa6b8d00
RDX: 0000000000000000 RSI: ffffffff8a6c1160 RDI: ffffffff8abf1360
RBP: ffffc90003257930 R08: dffffc0000000000 R09: fffffbfff2117049
R10: fffffbfff2117049 R11: 1ffffffff2117048 R12: 0000000000000001
R13: 1ffff9200064af10 R14: 0000000000000246 R15: dffffc0000000000
 rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
 rcu_read_lock include/linux/rcupdate.h:791 [inline]
 __d_lookup+0xa8/0x7c0 fs/dcache.c:2488
 lookup_fast+0x7c/0x4d0 fs/namei.c:1648
 walk_component fs/namei.c:1994 [inline]
 link_path_walk+0x5f2/0xe50 fs/namei.c:2325
 path_lookupat+0x9d/0x440 fs/namei.c:2478
 filename_lookup+0x1f0/0x500 fs/namei.c:2508
 user_path_at_empty+0x3e/0x60 fs/namei.c:2905
 do_readlinkat+0xd4/0x480 fs/stat.c:468
 __do_sys_readlink fs/stat.c:501 [inline]
 __se_sys_readlink fs/stat.c:498 [inline]
 __x64_sys_readlink+0x7b/0x90 fs/stat.c:498
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f138bb153a7
RSP: 002b:00007ffcd38016d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00007ffcd3801bb0 RCX: 00007f138bb153a7
RDX: 0000000000000400 RSI: 00007ffcd38016e0 RDI: 00007ffcd3801bb0
RBP: 00007ffcd38016e0 R08: 0000557d474fc104 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000400
R13: 00000000000000fe R14: 0000557d378aebe0 R15: 00007ffcd38026b0
 </TASK>
rcu: rcu_preempt kthread starved for 10340 jiffies! g123757 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:27712 pid:16    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5244 [inline]
 __schedule+0x10e9/0x40d0 kernel/sched/core.c:6561
 schedule+0xb9/0x180 kernel/sched/core.c:6637
 schedule_timeout+0x15c/0x280 kernel/time/timer.c:1965
 rcu_gp_fqs_loop+0x2f2/0x1310 kernel/rcu/tree.c:1706
 rcu_gp_kthread+0x95/0x380 kernel/rcu/tree.c:1905
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 1 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 1 skipped: idling at default_idle+0xb/0x10 arch/x86/kernel/process.c:735