syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (1 ticks this GP) idle=636/1/0x4000000000000000 softirq=106260/106260 fqs=0 
	(t=11170 jiffies g=204061 q=148)
rcu: rcu_preempt kthread starved for 11170 jiffies! g204061 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:29088 pid:   10 ppid:     2 flags:0x00004000
Call Trace:
 context_switch kernel/sched/core.c:3778 [inline]
 __schedule+0xea9/0x2230 kernel/sched/core.c:4527
 schedule+0xd0/0x2a0 kernel/sched/core.c:4602
 schedule_timeout+0x148/0x250 kernel/time/timer.c:1879
 rcu_gp_fqs_loop kernel/rcu/tree.c:1888 [inline]
 rcu_gp_kthread+0xae5/0x1b50 kernel/rcu/tree.c:2058
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
NMI backtrace for cpu 1
CPU: 1 PID: 2585 Comm: kworker/1:2 Not tainted 5.9.0-rc5-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: rcu_gp process_srcu
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x198/0x1fd lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x70/0xb1 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1b3/0x223 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x194/0x1cf kernel/rcu/tree_stall.h:318
 print_cpu_stall kernel/rcu/tree_stall.h:551 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:625 [inline]
 rcu_pending kernel/rcu/tree.c:3637 [inline]
 rcu_sched_clock_irq.cold+0x5b3/0xccd kernel/rcu/tree.c:2519
 update_process_times+0x25/0xa0 kernel/time/timer.c:1710
 tick_sched_handle+0x9b/0x180 kernel/time/tick-sched.c:176
 tick_sched_timer+0x1d1/0x2a0 kernel/time/tick-sched.c:1328
 __run_hrtimer kernel/time/hrtimer.c:1524 [inline]
 __hrtimer_run_queues+0x1d5/0xfc0 kernel/time/hrtimer.c:1588
 hrtimer_interrupt+0x32a/0x930 kernel/time/hrtimer.c:1650
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1080 [inline]
 __sysvec_apic_timer_interrupt+0x142/0x5e0 arch/x86/kernel/apic/apic.c:1097
 asm_call_on_stack+0xf/0x20 arch/x86/entry/entry_64.S:706
 </IRQ>
 __run_on_irqstack arch/x86/include/asm/irq_stack.h:22 [inline]
 run_on_irqstack_cond arch/x86/include/asm/irq_stack.h:48 [inline]
 sysvec_apic_timer_interrupt+0xb2/0xf0 arch/x86/kernel/apic/apic.c:1091
 asm_sysvec_apic_timer_interrupt+0x12/0x20 arch/x86/include/asm/idtentry.h:581
RIP: 0010:get_lock_parent_ip include/linux/ftrace.h:822 [inline]
RIP: 0010:preempt_latency_start kernel/sched/core.c:4165 [inline]
RIP: 0010:preempt_latency_start kernel/sched/core.c:4162 [inline]
RIP: 0010:preempt_count_add+0x74/0x140 kernel/sched/core.c:4190
Code: 0f b6 c0 3d f4 00 00 00 7f 64 65 8b 05 75 34 b2 7e 25 ff ff ff 7f 39 c3 74 03 5b 5d c3 48 8b 5c 24 10 48 89 df e8 cc 28 0b 00 <85> c0 75 35 65 48 8b 2c 25 c0 fe 01 00 48 8d bd d8 12 00 00 48 b8
RSP: 0018:ffffc90008817b88 EFLAGS: 00000283
RAX: 0000000000000000 RBX: ffffffff83b65978 RCX: 1ffffffff192e42c
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff83b65978
RBP: 000002ca05df2762 R08: 0000000000000040 R09: ffffc90016162d9f
R10: 0000000000000040 R11: 0000000000000000 R12: 0000000000000001
R13: 0000000000002ced R14: 0000000000000001 R15: dffffc0000000000
 delay_tsc+0x38/0xb0 arch/x86/lib/delay.c:79
 try_check_zero+0x1f5/0x330 kernel/rcu/srcutree.c:718
 srcu_advance_state kernel/rcu/srcutree.c:1158 [inline]
 process_srcu+0x2ec/0xea0 kernel/rcu/srcutree.c:1253
 process_one_work+0x94c/0x1670 kernel/workqueue.c:2269
 worker_thread+0x64c/0x1120 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:292
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294