INFO: rcu detected stall in prepare_to_swait_event

Status: auto-obsoleted due to no activity on 2026/10/10 22:23
Subsystems: kernel
Labels: prio:high
[Documentation on labels]
First crash: 94d, last: 94d
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ID Workflow Result Correct Bug Created Started Finished Revision
4e83fc6d assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ✅ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ✅ VMGuestTrigger: ✅ VMHostTrigger: ❌ ❓ INFO: rcu detected stall in prepare_to_swait_event 2026/07/14 00:44 2026/07/14 00:44 2026/07/14 01:24 2130f682

Sample crash report:
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	(detected by 0, t=10502 jiffies, g=45253, q=1695 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 6346 (4294978027-4294971681), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 6347 jiffies! g45253 f0x2 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:27656 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x17d9/0x56c0 kernel/sched/core.c:7234
 preempt_schedule_irq+0x4d/0xa0 kernel/sched/core.c:7556
 irqentry_exit_to_kernel_mode include/linux/irq-entry-common.h:539 [inline]
 irqentry_exit+0x14f/0x8f0 kernel/entry/common.c:167
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:preempt_schedule_thunk+0x0/0x40 arch/x86/entry/thunk.S:12
Code: 03 93 00 48 c7 c0 80 5a e0 8b c3 cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <55> 48 89 e5 57 56 52 51 50 41 50 41 51 41 52 41 53 e8 8a d9 9c 0a
RSP: 0018:ffffc90000157b60 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000282 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8e22a5a0 RDI: 00000000ffffffff
RBP: 0000000000000000 R08: ffffffff905775f7 R09: 1ffffffff20aeebe
R10: dffffc0000000000 R11: fffffbfff20aeebf R12: ffff88801dec0000
R13: 1ffff9200002af95 R14: ffffffff8eb5fd58 R15: ffffc90000157ca0
 __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:179 [inline]
 _raw_spin_unlock_irqrestore+0x74/0x80 kernel/locking/spinlock.c:198
 prepare_to_swait_event+0x322/0x350 kernel/sched/swait.c:120
 rcu_gp_fqs_loop+0x2d7/0x11f0 kernel/rcu/tree.c:2123
 rcu_gp_kthread+0x9e/0x2b0 kernel/rcu/tree.c:2325
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 UID: 0 PID: 5714 Comm: kworker/0:4 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Workqueue: events_power_efficient wg_ratelimiter_gc_entries
RIP: 0010:lock_release+0x5/0x3c0 kernel/locking/lockdep.c:5876
Code: e9 4f fe ff ff 41 bf 2f 00 00 00 e9 06 ff ff ff 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 55 <41> 57 41 56 41 55 41 54 53 48 83 ec 30 49 89 f5 49 89 fe 65 48 8b
RSP: 0018:ffffc900000065b8 EFLAGS: 00000202
RAX: 0000000000000001 RBX: ffffc900000066d8 RCX: 0000000080000101
RDX: ffffc90000006701 RSI: ffffffff8176f27f RDI: ffffffff8eb59c60
RBP: 1ffffffff21dd001 R08: ffffc900000066b8 R09: 0000000000000000
R10: ffffc90000006718 R11: fffff52000000ce5 R12: ffffc90000000000
R13: ffffffff8176f27f R14: ffffc900000066c8 R15: ffffc900000066c8
FS:  0000000000000000(0000) GS:ffff888124f58000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c3e4e8d CR3: 00000000574d4000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 rcu_lock_release include/linux/rcupdate.h:310 [inline]
 rcu_read_unlock include/linux/rcupdate.h:871 [inline]
 class_rcu_destructor include/linux/rcupdate.h:1183 [inline]
 unwind_next_frame+0x1baa/0x2550 arch/x86/kernel/unwind_orc.c:709
 __unwind_start+0x514/0x660 arch/x86/kernel/unwind_orc.c:787
 unwind_start arch/x86/include/asm/unwind.h:64 [inline]
 arch_stack_walk+0xe3/0x150 arch/x86/kernel/stacktrace.c:24
 stack_trace_save+0xa9/0x100 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2705 [inline]
 slab_free mm/slub.c:6405 [inline]
 kmem_cache_free+0x182/0x650 mm/slub.c:6532
 skb_ext_del include/linux/skbuff.h:5100 [inline]
 nf_bridge_info_free net/bridge/br_netfilter_hooks.c:157 [inline]
 br_nf_dev_queue_xmit+0x4f6/0x2540 net/bridge/br_netfilter_hooks.c:856
 NF_HOOK+0x64e/0x6e0 include/linux/netfilter.h:318
 br_nf_post_routing+0xa53/0xee0 net/bridge/br_netfilter_hooks.c:964
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_slow+0xc5/0x220 net/netfilter/core.c:619
 nf_hook include/linux/netfilter.h:273 [inline]
 NF_HOOK+0x23e/0x3f0 include/linux/netfilter.h:316
 br_forward_finish+0xd3/0x130 net/bridge/br_forward.c:66
 br_nf_hook_thresh net/bridge/br_netfilter_hooks.c:1165 [inline]
 br_nf_forward_finish+0xa76/0xea0 net/bridge/br_netfilter_hooks.c:667
 NF_HOOK+0x64e/0x6e0 include/linux/netfilter.h:318
 br_nf_forward_ip+0x7eb/0xa30 net/bridge/br_netfilter_hooks.c:721
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_slow+0xc5/0x220 net/netfilter/core.c:619
 nf_hook include/linux/netfilter.h:273 [inline]
 NF_HOOK+0x23e/0x3f0 include/linux/netfilter.h:316
 __br_forward+0x397/0x540 net/bridge/br_forward.c:115
 deliver_clone net/bridge/br_forward.c:131 [inline]
 maybe_deliver net/bridge/br_forward.c:191 [inline]
 br_flood+0x3e6/0x8d0 net/bridge/br_forward.c:245
 br_handle_frame_finish+0x1175/0x1990 net/bridge/br_input.c:229
 br_nf_hook_thresh+0x3dd/0x4c0 net/bridge/br_netfilter_hooks.c:-1
 br_nf_pre_routing_finish_ipv6+0x90c/0xc40 net/bridge/br_netfilter_ipv6.c:-1
 NF_HOOK include/linux/netfilter.h:318 [inline]
 br_nf_pre_routing_ipv6+0x382/0x6f0 net/bridge/br_netfilter_ipv6.c:183
 nf_hook_entry_hookfn include/linux/netfilter.h:158 [inline]
 nf_hook_bridge_pre net/bridge/br_input.c:291 [inline]
 br_handle_frame+0x127f/0x1510 net/bridge/br_input.c:442
 __netif_receive_skb_core+0x989/0x30b0 net/core/dev.c:6099
 __netif_receive_skb_one_core net/core/dev.c:6210 [inline]
 __netif_receive_skb net/core/dev.c:6325 [inline]
 process_backlog+0x706/0x1860 net/core/dev.c:6676
 __napi_poll+0xaa/0x330 net/core/dev.c:7735
 napi_poll net/core/dev.c:7798 [inline]
 net_rx_action+0x61d/0xf50 net/core/dev.c:7955
 handle_softirqs+0x225/0x840 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0xca/0x220 kernel/softirq.c:735
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:752
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1062
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:__might_resched+0xbb/0x4d0 kernel/sched/core.c:-1
Code: 74 28 80 3d 16 57 ab 0e 00 75 1f c6 05 0d 57 ab 0e 01 48 c7 c7 80 04 ec 8b be c7 23 00 00 48 c7 c2 00 19 ec 8b e8 75 ed 0c 00 <48> bd 00 00 00 00 00 fc ff df 65 44 8b 2d 83 ff d6 11 41 81 e5 ff
RSP: 0018:ffffc90003edfa50 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000046
RDX: 0000000000000000 RSI: ffffffff8e4af5f8 RDI: ffffffff8c4bd380
RBP: dffffc0000000000 R08: ffffffff8f774d43 R09: 1ffffffff1eee9a8
R10: dffffc0000000000 R11: fffffbfff1eee9a9 R12: ffff8880571b7bf8
R13: dffffc0000000000 R14: 0000000000000f7f R15: 0000000000000000
 wg_ratelimiter_gc_entries+0x3a4/0x450 drivers/net/wireguard/ratelimiter.c:78
 process_one_work kernel/workqueue.c:3322 [inline]
 process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
net_ratelimit: 3411 callbacks suppressed
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:fa:11:7d:48:06:49, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:1c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:fa:11:7d:48:06:49, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:1c, vlan:0)
net_ratelimit: 8393 callbacks suppressed
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:1c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:fa:11:7d:48:06:49, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:1c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/12 22:13 net 3f1f75536668 d78ea535 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce INFO: rcu detected stall in prepare_to_swait_event
* Struck through repros no longer work on HEAD.