syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P4261/1:b..l
	(detected by 1, t=10502 jiffies, g=10713, q=100 ncpus=2)
task:udevd           state:R  running task     stack:23776 pid:4261  ppid:3639   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:debug_lockdep_rcu_enabled+0x25/0x30 kernel/rcu/update.c:281
Code: 00 00 cc cc 00 31 c0 83 3d 47 32 09 04 00 74 1d 83 3d d2 65 09 04 00 74 14 65 48 8b 0d 64 57 ec 75 31 c0 83 b9 dc 0a 00 00 00 <0f> 94 c0 c3 00 00 cc cc 00 00 cc 48 8b 3c 24 e8 47 fb ff ff 66 90
RSP: 0018:ffffc90003d37960 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff88807fa79dc0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: dffffc0000000000 R08: dffffc0000000000 R09: fffff520000801cd
R10: fffff520000801cd R11: 1ffff920000801cc R12: ffff888026ce0620
R13: ffffc90000400e60 R14: 1ffff920000801cc R15: 00000000000401cc
 rcu_read_lock_held_common kernel/rcu/update.c:104 [inline]
 rcu_read_lock_held+0x6/0x40 kernel/rcu/update.c:309
 hlist_bl_first_rcu include/linux/rculist_bl.h:24 [inline]
 __d_lookup_rcu+0x138/0x4c0 fs/dcache.c:2384
 lookup_fast+0xca/0x4d0 fs/namei.c:1625
 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: 0033:0x7ff41af153a7
RSP: 002b:00007ffc257aea88 EFLAGS: 00000246 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00007ffc257af460 RCX: 00007ff41af153a7
RDX: 0000000000000400 RSI: 00007ffc257aef40 RDI: 00007ffc257af460
RBP: 00007ffc257af46f R08: 0000000000000075 R09: 0000000000000000
R10: 0000000000000100 R11: 0000000000000246 R12: 00007ffc257aef40
R13: 00007ffc257aeb40 R14: 0000557548dcb6d7 R15: 000055754e022220
 </TASK>
rcu: rcu_preempt kthread starved for 10530 jiffies! g10713 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
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:27840 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 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:51 [inline]
NMI backtrace for cpu 0 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:89 [inline]
NMI backtrace for cpu 0 skipped: idling at default_idle+0xb/0x10 arch/x86/kernel/process.c:741