syzbot

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (1 GPs behind) idle=18b/1/0x4000000000000004 softirq=25062/25063 fqs=38 
	(t=10500 jiffies g=34301 q=24)
rcu: rcu_preempt kthread starved for 10423 jiffies! g34301 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:26960 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
 rcu_gp_fqs_loop+0x2be/0x11d0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x9b/0x370 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 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:729
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
 rcu_dump_cpu_stacks+0x22f/0x380 kernel/rcu/tree_stall.h:349
 print_cpu_stall+0x31d/0x5f0 kernel/rcu/tree_stall.h:633
 check_cpu_stall kernel/rcu/tree_stall.h:727 [inline]
 rcu_pending kernel/rcu/tree.c:3936 [inline]
 rcu_sched_clock_irq+0x6ea/0x1120 kernel/rcu/tree.c:2619
 update_process_times+0x193/0x200 kernel/time/timer.c:2021
 tick_sched_handle kernel/time/tick-sched.c:254 [inline]
 tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4b4/0xb70 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x3bb/0x8d0 kernel/time/hrtimer.c:1811
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
 __sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0x4d/0xc0 arch/x86/kernel/apic/apic.c:1108
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:__sanitizer_cov_trace_cmp4+0x0/0x80 kernel/kcov.c:267
Code: 28 4d 39 ca 77 22 89 ff 89 f6 4a c7 44 02 08 02 00 00 00 4a 89 7c 02 10 4a 89 74 02 18 4a 89 44 02 20 48 ff c1 48 89 0a c3 90 <48> 8b 04 24 65 48 8b 0d 44 4d 89 7e 65 8b 15 45 4d 89 7e 81 e2 00
RSP: 0000:ffffc90000dd01d8 EFLAGS: 00000246
RAX: ffffffff881463bc RBX: 0000000000000db8 RCX: ffff88813fe68000
RDX: 0000000000000100 RSI: 00000000000006db RDI: 00000000000006db
RBP: 00000000000006db R08: ffffffff901d418f R09: 1ffffffff203a831
R10: dffffc0000000000 R11: fffffbfff203a832 R12: 0000000000000000
R13: 00000000000006db R14: 00000000000006db R15: 00000000000006db
 cake_heapify+0x28e/0x6a0 net/sched/sch_cake.c:1503
 cake_drop net/sched/sch_cake.c:1575 [inline]
 cake_enqueue+0x33d9/0x7fc0 net/sched/sch_cake.c:1949
 dev_qdisc_enqueue+0x48/0x210 net/core/dev.c:3865
 __dev_xmit_skb net/core/dev.c:3949 [inline]
 __dev_queue_xmit+0xc25/0x2f80 net/core/dev.c:4266
 tipc_l2_send_msg+0x30a/0x3c0 net/tipc/bearer.c:518
 tipc_bearer_xmit_skb+0x292/0x3c0 net/tipc/bearer.c:577
 tipc_disc_timeout+0x57d/0x6d0 net/tipc/discover.c:338
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
 expire_timers kernel/time/timer.c:1699 [inline]
 __run_timers+0x53e/0x800 kernel/time/timer.c:1970
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
 handle_softirqs+0x339/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:do_idle+0x0/0x580 kernel/sched/idle.c:262
Code: 1d 69 00 f0 80 0b 08 31 c0 5b c3 89 f9 80 e1 07 80 c1 03 38 c1 7c d1 48 89 fb e8 6b 1c 69 00 48 89 df eb c4 66 0f 1f 44 00 00 <55> 48 89 e5 41 57 41 56 41 55 41 54 53 48 83 e4 e0 48 81 ec e0 00
RSP: 0000:ffffc90000d67e88 EFLAGS: 00000246
RAX: b03ad572c0312400 RBX: 0000000000000098 RCX: ffffffff89c4ad77
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffff88813fe68000
RBP: ffffc90000d67f48 R08: ffff88813fe68007 R09: 1ffff11027fcd000
R10: dffffc0000000000 R11: ffffed1027fcd001 R12: dffffc0000000000
R13: 00000000014fb16c R14: ffffffff8be31828 R15: ffff8880b9121528
 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:403
 start_secondary+0x330/0x430 arch/x86/kernel/smpboot.c:281
 secondary_startup_64_no_verify+0xb1/0xbb
 </TASK>