rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	1-...!: (0 ticks this GP) idle=52cc/1/0x4000000000000000 softirq=43960/43960 fqs=0
rcu: 	(detected by 0, t=10505 jiffies, g=31225, q=608 ncpus=2)
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 9786 Comm: syz.0.940 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:hrtimer_try_to_cancel+0x1e6/0x420
Code: 80 e1 07 80 c1 03 38 c1 7c ea 48 89 df e8 d2 99 75 00 eb e0 e8 cb 19 12 00 e9 ce fe ff ff e8 c1 19 12 00 eb 05 e8 ba 19 12 00 <4c> 8b 64 24 08 48 8b 44 24 10 42 80 3c 30 00 74 08 4c 89 e7 e8 d1
RSP: 0018:ffffc900001e0928 EFLAGS: 00000006
RAX: ffffffff81ada746 RBX: ffff888136627b10 RCX: ffff888021595640
RDX: 0000000000010000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00000000002f52ae R08: ffff888136627a83 R09: 1ffff11026cc4f50
R10: dffffc0000000000 R11: ffffed1026cc4f51 R12: 1ffff11026cc4f62
R13: ffff888136627b48 R14: dffffc0000000000 R15: ffff888136627b00
FS:  00007fb4ccca36c0(0000) GS:ffff8881a3c13000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000012375c000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000200000000300 DR2: 0000200000000300
DR3: 0000200000000300 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 hrtimer_cancel+0x3b/0x50
 cpu_clock_event_stop+0xd9/0x130
 __perf_event_overflow+0x580/0xe40
 perf_swevent_hrtimer+0x3c5/0x550
 __hrtimer_run_queues+0x4e0/0xc60
 hrtimer_interrupt+0x45b/0xaa0
 __sysvec_apic_timer_interrupt+0x10b/0x410
 sysvec_apic_timer_interrupt+0xa1/0xc0
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20
RIP: 0010:lock_acquire+0xbf/0x360
Code: 84 fa 00 00 00 65 8b 05 5f a0 03 11 85 c0 0f 85 eb 00 00 00 65 48 8b 04 25 08 d0 a0 92 83 b8 ec 0a 00 00 00 0f 85 d5 00 00 00 <48> c7 44 24 30 00 00 00 00 9c 8f 44 24 30 4c 89 74 24 10 4d 89 fe
RSP: 0018:ffffc90002d8f358 EFLAGS: 00000246
RAX: ffff888021595640 RBX: 0000000000000000 RCX: bc0e4e00f5700700
RDX: 0000000000000000 RSI: ffffffff8172d1b2 RDI: 1ffffffff1c27424
RBP: ffffffff8172d195 R08: 0000000000000000 R09: 0000000000000000
R10: ffffc90002d8f518 R11: ffffffff81ac4d00 R12: 0000000000000002
R13: ffffffff8e13a120 R14: 0000000000000000 R15: 0000000000000000
 unwind_next_frame+0xc2/0x2390
 arch_stack_walk+0x11c/0x150
 stack_trace_save+0x9c/0xe0
 kasan_save_track+0x3e/0x80
 __kasan_slab_alloc+0x6c/0x80
 kmem_cache_alloc_node_noprof+0x1bb/0x3c0
 __alloc_skb+0x112/0x2d0
 sock_wmalloc+0xb2/0x130
 l2tp_ip_sendmsg+0x1bb/0x1650
 __sock_sendmsg+0x19c/0x270
 ____sys_sendmsg+0x505/0x830
 ___sys_sendmsg+0x21f/0x2a0
 __x64_sys_sendmsg+0x19b/0x260
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb4cbd8eba9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb4ccca3038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fb4cbfd6090 RCX: 00007fb4cbd8eba9
RDX: 000000000400c080 RSI: 0000200000000340 RDI: 000000000000000b
RBP: 00007fb4cbe11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb4cbfd6128 R14: 00007fb4cbfd6090 R15: 00007ffc6da31058
 </TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10504 jiffies! g31225 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=1 timer-softirq=11402
rcu: rcu_preempt kthread starved for 10505 jiffies! g31225 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->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:I stack:27160 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00004000
Call Trace:
 <TASK>
 __schedule+0x1798/0x4cc0
 schedule+0x165/0x360
 schedule_timeout+0x12b/0x270
 rcu_gp_fqs_loop+0x301/0x1540
 rcu_gp_kthread+0x99/0x390
 kthread+0x711/0x8a0
 ret_from_fork+0x439/0x7d0
 ret_from_fork_asm+0x1a/0x30
 </TASK>
