syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P4445/1:b..l
	(detected by 0, t=10502 jiffies, g=6113, q=869)
task:modprobe        state:R  running task     stack:27200 pid: 4445 ppid:  4276 flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5030 [inline]
 __schedule+0x11b8/0x43b0 kernel/sched/core.c:6376
 preempt_schedule_irq+0xb1/0x150 kernel/sched/core.c:6780
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:rcu_is_watching+0x63/0xa0 kernel/rcu/tree.c:1124
Code: 89 f7 e8 50 9d 59 00 48 c7 c3 c8 b2 03 00 49 03 1e 48 89 d8 48 c1 e8 03 42 0f b6 04 38 84 c0 75 2b 8b 03 65 ff 0d c5 d2 9e 7e <74> 08 24 01 5b 41 5e 41 5f c3 e8 86 dd 9c ff eb f1 48 c7 c7 20 0c
RSP: 0018:ffffc9000345fd18 EFLAGS: 00000286
RAX: 000000000000ad3d RBX: ffff8880b913b2c8 RCX: 12306b4a17260300
RDX: 0000000000000000 RSI: ffffffff8a59a720 RDI: ffffffff8a59a6e0
RBP: 0000000000000cc0 R08: dffffc0000000000 R09: fffffbfff1ff3619
R10: fffffbfff1ff3619 R11: 1ffffffff1ff3618 R12: 0000000000000001
R13: 1ffff9200068bfd0 R14: ffffffff8bbaf818 R15: dffffc0000000000
 rcu_read_lock_held_common kernel/rcu/update.c:108 [inline]
 rcu_read_lock_held+0x11/0x40 kernel/rcu/update.c:309
 task_css include/linux/cgroup.h:496 [inline]
 mem_cgroup_from_task+0x96/0x110 mm/memcontrol.c:935
 get_obj_cgroup_from_current+0x146/0x2f0 mm/memcontrol.c:2926
 memcg_slab_pre_alloc_hook mm/slab.h:283 [inline]
 slab_pre_alloc_hook+0x7e/0xc0 mm/slab.h:497
 slab_alloc_node mm/slub.c:3134 [inline]
 slab_alloc mm/slub.c:3228 [inline]
 kmem_cache_alloc+0x3d/0x290 mm/slub.c:3233
 prepare_creds+0x3c/0x610 kernel/cred.c:260
 access_override_creds fs/open.c:352 [inline]
 do_faccessat+0xfc/0xa50 fs/open.c:416
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fac21cec2c7
RSP: 002b:00007ffda47e1e68 EFLAGS: 00000246 ORIG_RAX: 0000000000000015
RAX: ffffffffffffffda RBX: 00007fac21bce4d0 RCX: 00007fac21cec2c7
RDX: 00005641215a6010 RSI: 0000000000000000 RDI: 00007fac21bc7326
RBP: 0000000000000004 R08: 00000000000001e0 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffda47e1f58
R13: 00007ffda47e1f80 R14: 00007fac21bce4d0 R15: 0000000000000000
 </TASK>
rcu: rcu_preempt kthread starved for 9840 jiffies! g6113 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:27904 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5030 [inline]
 __schedule+0x11b8/0x43b0 kernel/sched/core.c:6376
 schedule+0x11b/0x1e0 kernel/sched/core.c:6459
 schedule_timeout+0x15c/0x280 kernel/time/timer.c:1914
 rcu_gp_fqs_loop+0x29e/0x11b0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x98/0x350 kernel/rcu/tree.c:2145
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </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:722