INFO: rcu detected stall in neigh_periodic_work

Status: upstream: reported syz repro on 2025/06/04 08:32
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+929f9d5abf02856a21ce@syzkaller.appspotmail.com
First crash: 477d, last: 58d
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/06/05 upstream (ToT) 16b70698aa3a syz [report] INFO: rcu detected stall in worker_thread
2026/09/21 upstream (ToT) [unknown] syz Failed due to an error; will retry later
▶ ▼ Similar bugs (7)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in neigh_periodic_work (5) prio:normal net 1 syz error error 1 19d 265d 0/29 upstream: reported syz repro on 2026/01/02 09:02
linux-5.15 INFO: rcu detected stall in neigh_periodic_work origin:lts-only 1 syz, C error 1 216d 216d 0/3 upstream: reported C repro on 2026/02/20 05:23
upstream INFO: rcu detected stall in neigh_periodic_work (2) net 1 syz, C error 2 927d 1099d 0/29 closed as invalid on 2024/03/13 18:06
upstream INFO: rcu detected stall in neigh_periodic_work (4) net 1 1 510d 510d 0/29 auto-obsoleted due to no activity on 2025/07/31 09:55
upstream BUG: soft lockup in neigh_periodic_work net 1 2 631d 663d 0/29 closed as invalid on 2025/01/28 16:26
upstream INFO: rcu detected stall in neigh_periodic_work (3) net 1 2 865d 885d 0/29 auto-obsoleted due to no activity on 2024/08/09 21:19
upstream INFO: rcu detected stall in neigh_periodic_work net 1 1 1294d 1294d 0/29 auto-obsoleted due to no activity on 2023/06/07 17:40
▶ ▼ Fix bisection attempts (3)
Created Duration User Patch Repo Result
2026/01/22 09:05 0m bisect fix linux-6.1.y error job log
2025/12/17 01:32 1h53m bisect fix linux-6.1.y OK (0) job log log
2025/08/15 15:37 2h32m bisect fix linux-6.1.y OK (0) job log log

Sample crash report:
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-...!: (10500 ticks this GP) idle=55fc/1/0x4000000000000000 softirq=11229/11229 fqs=0
	(t=10500 jiffies g=13461 q=552 ncpus=2)
rcu: rcu_preempt kthread timer wakeup didn't happen for 10499 jiffies! g13461 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=0 timer-softirq=6848
rcu: rcu_preempt kthread starved for 10500 jiffies! g13461 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->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:I stack:26912 pid:16    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5244 [inline]
 __schedule+0x10e9/0x40d0 kernel/sched/core.c:6561
 schedule+0xb9/0x180 kernel/sched/core.c:6637
 schedule_timeout+0x15c/0x280 kernel/time/timer.c:1965
 rcu_gp_fqs_loop+0x2f2/0x1310 kernel/rcu/tree.c:1706
 rcu_gp_kthread+0x95/0x380 kernel/rcu/tree.c:1905
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 PID: 4324 Comm: kworker/0:11 Not tainted 6.1.140-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: wg-crypt-wg0 wg_packet_tx_worker
RIP: 0010:queued_write_lock_slowpath+0x11d/0x24f kernel/locking/qrwlock.c:85
Code: b8 f7 f0 81 0b 00 01 00 00 43 0f b6 04 27 84 c0 74 35 89 d9 80 e1 07 80 c1 03 38 c1 7c 29 48 89 df e8 a7 ed b8 f7 eb 1f f3 90 <43> 0f b6 04 27 84 c0 74 14 89 d9 80 e1 07 80 c1 03 38 c1 7c 08 48
RSP: 0018:ffffc90003287500 EFLAGS: 00000206
RAX: 00000000000001ff RBX: ffffffff8dc3ed60 RCX: ffffffff8a195f35
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff8dc3ed60
RBP: ffffc900032875b0 R08: dffffc0000000000 R09: fffffbfff1b87dad
R10: fffffbfff1b87dad R11: 1ffffffff1b87dac R12: dffffc0000000000
R13: 1ffff92000650ea4 R14: ffffc90003287550 R15: 1ffffffff1b87dac
FS:  0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055c7cf982ca0 CR3: 0000000057076000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 queued_write_lock include/asm-generic/qrwlock.h:101 [inline]
 do_raw_write_lock+0x1ea/0x250 kernel/locking/spinlock_debug.c:210
 ___neigh_create+0xe61/0x24c0 net/core/neighbour.c:682
 ip6_finish_output2+0x14f0/0x1590 net/ipv6/ip6_output.c:129
 __ip6_finish_output net/ipv6/ip6_output.c:205 [inline]
 ip6_finish_output+0x5d3/0xa60 net/ipv6/ip6_output.c:216
 ip6tunnel_xmit include/net/ip6_tunnel.h:161 [inline]
 udp_tunnel6_xmit_skb+0x5a0/0xa10 net/ipv6/ip6_udp_tunnel.c:109
 send6+0x59f/0x8b0 drivers/net/wireguard/socket.c:152
 wg_socket_send_skb_to_peer+0x10d/0x1c0 drivers/net/wireguard/socket.c:178
 wg_packet_create_data_done drivers/net/wireguard/send.c:251 [inline]
 wg_packet_tx_worker+0x1c4/0x7c0 drivers/net/wireguard/send.c:276
 process_one_work+0x898/0x1160 kernel/workqueue.c:2292
 worker_thread+0xaa2/0x1250 kernel/workqueue.c:2439
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
CPU: 0 PID: 4324 Comm: kworker/0:11 Not tainted 6.1.140-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: wg-crypt-wg0 wg_packet_tx_worker
RIP: 0010:queued_write_lock_slowpath+0x11d/0x24f kernel/locking/qrwlock.c:85
Code: b8 f7 f0 81 0b 00 01 00 00 43 0f b6 04 27 84 c0 74 35 89 d9 80 e1 07 80 c1 03 38 c1 7c 29 48 89 df e8 a7 ed b8 f7 eb 1f f3 90 <43> 0f b6 04 27 84 c0 74 14 89 d9 80 e1 07 80 c1 03 38 c1 7c 08 48
RSP: 0018:ffffc90003287500 EFLAGS: 00000206
RAX: 00000000000001ff RBX: ffffffff8dc3ed60 RCX: ffffffff8a195f35
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff8dc3ed60
RBP: ffffc900032875b0 R08: dffffc0000000000 R09: fffffbfff1b87dad
R10: fffffbfff1b87dad R11: 1ffffffff1b87dac R12: dffffc0000000000
R13: 1ffff92000650ea4 R14: ffffc90003287550 R15: 1ffffffff1b87dac
FS:  0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055c7cf982ca0 CR3: 0000000057076000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 queued_write_lock include/asm-generic/qrwlock.h:101 [inline]
 do_raw_write_lock+0x1ea/0x250 kernel/locking/spinlock_debug.c:210
 ___neigh_create+0xe61/0x24c0 net/core/neighbour.c:682
 ip6_finish_output2+0x14f0/0x1590 net/ipv6/ip6_output.c:129
 __ip6_finish_output net/ipv6/ip6_output.c:205 [inline]
 ip6_finish_output+0x5d3/0xa60 net/ipv6/ip6_output.c:216
 ip6tunnel_xmit include/net/ip6_tunnel.h:161 [inline]
 udp_tunnel6_xmit_skb+0x5a0/0xa10 net/ipv6/ip6_udp_tunnel.c:109
 send6+0x59f/0x8b0 drivers/net/wireguard/socket.c:152
 wg_socket_send_skb_to_peer+0x10d/0x1c0 drivers/net/wireguard/socket.c:178
 wg_packet_create_data_done drivers/net/wireguard/send.c:251 [inline]
 wg_packet_tx_worker+0x1c4/0x7c0 drivers/net/wireguard/send.c:276
 process_one_work+0x898/0x1160 kernel/workqueue.c:2292
 worker_thread+0xaa2/0x1250 kernel/workqueue.c:2439
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 4405 Comm: kworker/1:8 Not tainted 6.1.140-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Workqueue: events_power_efficient neigh_periodic_work
RIP: 0010:hlock_class kernel/locking/lockdep.c:228 [inline]
RIP: 0010:__lock_acquire+0x10ba/0x7c50 kernel/locking/lockdep.c:5045
Code: 03 89 c3 81 e3 ff 1f 00 00 c1 e8 03 25 f8 03 00 00 48 8d b8 40 82 8b 90 be 08 00 00 00 e8 1e 4f 6f 00 48 0f a3 1d b6 82 28 0f <0f> 83 8c 01 00 00 48 8d 04 5b c1 e0 06 48 8d 98 00 01 24 90 49 b8
RSP: 0018:ffffc900001e0860 EFLAGS: 00000057
RAX: 0000000000000001 RBX: 000000000000005e RCX: ffffffff8162ff82
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff908b8248
RBP: ffffc900001e0ab0 R08: dffffc0000000000 R09: fffffbfff211704a
R10: fffffbfff211704a R11: 1ffffffff2117049 R12: 00000000cf82e703
R13: 00000000c2fd2ede R14: 00000000b144b952 R15: ffff88802efaa890
FS:  0000000000000000(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055afda3809e8 CR3: 000000000c68e000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0xa4/0xf0 kernel/locking/spinlock.c:162
 debug_object_activate+0x6a/0x490 lib/debugobjects.c:698
 debug_hrtimer_activate kernel/time/hrtimer.c:411 [inline]
 debug_activate kernel/time/hrtimer.c:466 [inline]
 enqueue_hrtimer+0x30/0x3f0 kernel/time/hrtimer.c:1075
 __run_hrtimer kernel/time/hrtimer.c:1708 [inline]
 __hrtimer_run_queues+0x642/0xc80 kernel/time/hrtimer.c:1755
 hrtimer_interrupt+0x3bb/0x8d0 kernel/time/hrtimer.c:1817
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1107 [inline]
 __sysvec_apic_timer_interrupt+0x153/0x5a0 arch/x86/kernel/apic/apic.c:1124
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
 sysvec_apic_timer_interrupt+0x9b/0xc0 arch/x86/kernel/apic/apic.c:1118
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa5/0x100 kernel/locking/spinlock.c:194
Code: 74 05 e8 2e f7 6d f7 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f6 44 24 21 02 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> b6 71 3e f7 65 8b 05 57 33 e9 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc90003587a20 EFLAGS: 00000206
RAX: d2679d600dfcc800 RBX: 0000000000000a02 RCX: d2679d600dfcc800
RDX: dffffc0000000000 RSI: ffffffff8a6c0000 RDI: 0000000000000001
RBP: ffffc90003587ab0 R08: dffffc0000000000 R09: fffffbfff2117050
R10: fffffbfff2117050 R11: 1ffffffff211704f R12: dffffc0000000000
R13: ffff888059eb7af8 R14: ffffffff96cde3a0 R15: 1ffff920006b0f44
 debug_rcu_head_queue kernel/rcu/rcu.h:191 [inline]
 kvfree_call_rcu+0xcb/0x870 kernel/rcu/tree.c:3392
 neigh_periodic_work+0x3f3/0xd70 net/core/neighbour.c:1005
 process_one_work+0x898/0x1160 kernel/workqueue.c:2292
 worker_thread+0xaa2/0x1250 kernel/workqueue.c:2439
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/04 08:31 linux-6.1.y da3c5173c55f a30356b7 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in neigh_periodic_work
2026/07/27 23:42 linux-6.1.y dc5c83b7f5f8 aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan INFO: rcu detected stall in neigh_periodic_work
* Struck through repros no longer work on HEAD.