[v5.15] INFO: rcu detected stall in neigh_periodic_work

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3330a8d33e08 Linux 5.15.201
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1030195a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=353ae28c40b35af5
dashboard link: https://syzkaller.appspot.com/bug?extid=c1840ef6b191b1b798d0
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=138fdc02580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1591715a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/805fe5d5059e/disk-3330a8d3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/27b51f6fcd64/vmlinux-3330a8d3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/c9998071ec80/bzImage-3330a8d3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c1840e...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 0-...!: (0 ticks this GP) idle=6e3/1/0x4000000000000002 softirq=6980/6980 fqs=16
(detected by 1, t=10502 jiffies, g=7789, q=81)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 1235 Comm: kworker/u4:4 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: netns cleanup_net
RIP: 0010:trace_hardirqs_off_finish+0x45/0x1f0 kernel/trace/trace_preemptirq.c:66
Code: 85 db 74 0a e8 1c d2 f9 ff e9 a8 00 00 00 65 c7 05 c4 e2 83 7e 01 00 00 00 65 8b 1d 8d 1f 83 7e 89 de 81 e6 00 00 f0 00 31 ff <e8> 56 d5 f9 ff 81 e3 00 00 f0 00 74 07 e8 e9 d1 f9 ff eb 78 48 8b
RSP: 0018:ffffc90004ff7168 EFLAGS: 00000046
RAX: ffffffff817f501b RBX: 0000000000000201 RCX: ffff888022afbb80
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8880b9000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f27cf283dac CR3: 000000001fe04000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
irqentry_enter+0x33/0x50 kernel/entry/common.c:384
sysvec_irq_work+0xa/0xc0 arch/x86/kernel/irq_work.c:17
asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:713
RIP: 0010:rcu_read_unlock_special+0x7f/0x4a0 kernel/rcu/tree_plugin.h:674
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 e2 f0 9c 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 20 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc90004ff7260 EFLAGS: 00000206
RAX: 430cf048634cfd00 RBX: 1ffff920009fee50 RCX: 430cf048634cfd00
RDX: dffffc0000000000 RSI: ffffffff8a2b2780 RDI: ffffffff8a79f800
RBP: ffffc90004ff7328 R08: ffffffff901d30ff R09: 1ffffffff203a61f
R10: dffffc0000000000 R11: fffffbfff203a620 R12: ffffffff8c322f00
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
__rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:422
rcu_read_unlock include/linux/rcupdate.h:772 [inline]
__neigh_notify+0x282/0x2e0 net/core/neighbour.c:3395
neigh_cleanup_and_release+0x9d/0x250 net/core/neighbour.c:101
neigh_flush_dev+0x184/0x990 net/core/neighbour.c:374
__neigh_ifdown+0x39/0x3a0 net/core/neighbour.c:391
neigh_ifdown+0x1b/0x30 net/core/neighbour.c:408
rt6_disable_ip+0x616/0x6b0 net/ipv6/route.c:4922
addrconf_ifdown+0x155/0x19c0 net/ipv6/addrconf.c:3775
addrconf_notify+0x445/0xf00 net/ipv6/addrconf.c:-1
notifier_call_chain kernel/notifier.c:83 [inline]
raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:391
call_netdevice_notifiers_extack net/core/dev.c:2074 [inline]
call_netdevice_notifiers net/core/dev.c:2088 [inline]
dev_close_many+0x29f/0x400 net/core/dev.c:1663
unregister_netdevice_many+0x481/0x19f0 net/core/dev.c:11123
ip6gre_exit_batch_net+0x44d/0x4a0 net/ipv6/ip6_gre.c:1657
ops_exit_list net/core/net_namespace.c:177 [inline]
cleanup_net+0x791/0xba0 net/core/net_namespace.c:635
process_one_work+0x85f/0x1010 kernel/workqueue.c:2310
worker_thread+0xaa6/0x1290 kernel/workqueue.c:2457
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>
rcu: rcu_preempt kthread starved for 10420 jiffies! g7789 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:28016 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:
NMI backtrace for cpu 1
CPU: 1 PID: 4298 Comm: kworker/1:19 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: events_power_efficient neigh_periodic_work
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_check_gp_kthread_starvation+0x1cd/0x250 kernel/rcu/tree_stall.h:487
print_other_cpu_stall+0x1110/0x1270 kernel/rcu/tree_stall.h:592
check_cpu_stall kernel/rcu/tree_stall.h:745 [inline]
rcu_pending kernel/rcu/tree.c:3936 [inline]
rcu_sched_clock_irq+0x843/0x1120 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+0x4ad/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+0x9b/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:queued_write_lock_slowpath+0x129/0x270 kernel/locking/qrwlock.c:78
Code: f0 41 81 0e 00 01 00 00 43 0f b6 04 27 84 c0 74 37 44 89 f1 80 e1 07 80 c1 03 38 c1 7c 2a 4c 89 f7 e8 2b c5 5f 00 eb 20 f3 90 <43> 0f b6 04 27 84 c0 74 15 44 89 f1 80 e1 07 80 c1 03 38 c1 7c 08
RSP: 0018:ffffc9000314fa40 EFLAGS: 00000206
RAX: 00000000000001ff RBX: ffffc9000314fa90 RCX: ffffffff815e68bf
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff8d53bb58
RBP: ffffc9000314faf0 R08: ffffffff8d53bb5b R09: 1ffffffff1aa776b
R10: dffffc0000000000 R11: fffffbfff1aa776c R12: dffffc0000000000
R13: 1ffff92000629f4c R14: ffffffff8d53bb58 R15: 1ffffffff1aa776b
queued_write_lock include/asm-generic/qrwlock.h:97 [inline]
do_raw_write_lock+0x1e6/0x260 kernel/locking/spinlock_debug.c:210
neigh_periodic_work+0x57/0xc70 net/core/neighbour.c:898
process_one_work+0x85f/0x1010 kernel/workqueue.c:2310
worker_thread+0xaa6/0x1290 kernel/workqueue.c:2457
kthread+0x436/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>


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