syzbot


INFO: rcu detected stall in kthreadd (2)

Status: upstream: reported on 2026/01/27 21:22
Reported-by: syzbot+c557e44005febbf6663e@syzkaller.appspotmail.com
First crash: 103d, last: 29d
Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.6 INFO: rcu detected stall in kthreadd 1 1 260d 260d 0/2 auto-obsoleted due to no activity on 2025/12/02 17:39
linux-6.1 INFO: rcu detected stall in kthreadd 1 1 726d 726d 0/3 auto-obsoleted due to no activity on 2024/08/23 07:20
upstream INFO: rcu detected stall in kthreadd (2) mm 1 C unreliable error 115 7d05h 558d 0/29 upstream: reported C repro on 2024/10/30 03:07
upstream INFO: rcu detected stall in kthreadd mm 1 2 745d 757d 0/29 auto-obsoleted due to no activity on 2024/07/25 04:06
android-5-15 BUG: soft lockup in kthreadd (2) 1 1 502d 502d 0/2 auto-obsoleted due to no activity on 2025/03/25 17:14
android-5-15 BUG: soft lockup in kthreadd origin:lts 1 C 2 652d 672d 0/2 auto-obsoleted due to no activity on 2024/11/05 13:04

Sample crash report:
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P2/1:b..l
rcu: 	(detected by 1, t=10503 jiffies, g=15777, q=284 ncpus=2)
task:kthreadd        state:R  running task     stack:27176 pid:2     ppid:0      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 preempt_schedule_irq+0xbf/0x150 kernel/sched/core.c:7010
 irqentry_exit+0x67/0x70 kernel/entry/common.c:438
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:lock_acquire+0x208/0x420 kernel/locking/lockdep.c:5758
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3c 04 f8 0f 85 f0 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 3c 00 00 00 00 43 c7 44 3c 08 00 00 00 00 65 48 8b 04 25
RSP: 0018:ffffc90000077420 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 2093b10b7e42a300
RDX: 0000000000000000 RSI: ffffffff8acadb60 RDI: ffffffff8b1c8e60
RBP: ffffc90000077540 R08: dffffc0000000000 R09: 1ffffffff2238aa0
R10: dffffc0000000000 R11: fffffbfff2238aa1 R12: 1ffff9200000ee90
R13: ffffffff8d1320a0 R14: 0000000000000246 R15: dffffc0000000000
 rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 rcu_read_lock include/linux/rcupdate.h:786 [inline]
 page_ext_get+0x3e/0x2b0 mm/page_ext.c:508
 __page_table_check_zero+0x138/0x4b0 mm/page_table_check.c:148
 page_table_check_free include/linux/page_table_check.h:41 [inline]
 free_pages_prepare mm/page_alloc.c:1182 [inline]
 free_unref_page_prepare+0x7c1/0x8c0 mm/page_alloc.c:2365
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2458
 discard_slab mm/slub.c:2127 [inline]
 __unfreeze_partials+0x1cf/0x210 mm/slub.c:2667
 put_cpu_partial+0x17c/0x250 mm/slub.c:2743
 __slab_free+0x319/0x400 mm/slub.c:3700
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xd0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6e/0x4b0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 __kmem_cache_alloc_node+0x13a/0x250 mm/slub.c:3534
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc+0xa4/0x230 mm/slab_common.c:1020
 kmalloc include/linux/slab.h:604 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 lsm_task_alloc security/security.c:655 [inline]
 security_task_alloc+0x46/0x130 security/security.c:2888
 copy_process+0x1529/0x3d80 kernel/fork.c:2489
 kernel_clone+0x24b/0x8a0 kernel/fork.c:2915
 kernel_thread+0x13f/0x1b0 kernel/fork.c:2977
 create_kthread kernel/kthread.c:411 [inline]
 kthreadd+0x57f/0x750 kernel/kthread.c:766
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
rcu: rcu_preempt kthread starved for 1581 jiffies! g15777 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:27656 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 schedule_timeout+0x188/0x2d0 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x313/0x1590 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x9d/0x3b0 kernel/rcu/tree.c:1866
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 7298 Comm: syz.3.247 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
RIP: 0010:allocate_slab mm/slub.c:-1 [inline]
RIP: 0010:new_slab+0x90/0x2d0 mm/slub.c:2081
Code: 0f b7 4b 3a 39 c8 76 0e 89 ef 81 e7 ff 53 f6 ff 81 cf 00 20 09 00 44 89 e6 44 89 fa e8 99 20 00 00 48 85 c0 0f 84 1a 01 00 00 <49> 89 c6 44 89 f8 c1 e0 10 25 00 00 ff 7f 41 89 46 28 45 89 fc 41
RSP: 0018:ffffc90000006de0 EFLAGS: 00000282
RAX: ffffea0000f29580 RBX: ffff88801e6693c0 RCX: 92420beb9140b800
RDX: 0000000000000000 RSI: ffffffff8b1c8e40 RDI: ffffffff8b1c8e00
RBP: 0000000000000820 R08: ffffffff8e8b14ef R09: 1ffffffff1d1629d
R10: dffffc0000000000 R11: fffffbfff1d1629e R12: 00000000ffffffff
R13: 0000000000000001 R14: 0000000000000001 R15: 0000000000000010
FS:  00007f1a51e2d6c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555592acc4e8 CR3: 0000000025481000 CR4: 00000000003506f0
DR0: 0000000000000008 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 ___slab_alloc+0xc5d/0x12f0 mm/slub.c:3253
 __slab_alloc mm/slub.c:3339 [inline]
 __slab_alloc_node mm/slub.c:3392 [inline]
 slab_alloc_node mm/slub.c:3485 [inline]
 slab_alloc mm/slub.c:3503 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3510 [inline]
 kmem_cache_alloc+0x1b3/0x2d0 mm/slub.c:3519
 skb_ext_maybe_cow net/core/skbuff.c:6664 [inline]
 skb_ext_add+0x1b3/0x8e0 net/core/skbuff.c:6738
 nf_bridge_unshare net/bridge/br_netfilter_hooks.c:165 [inline]
 br_nf_forward_ip+0xc6/0x1110 net/bridge/br_netfilter_hooks.c:709
 nf_hook_entry_hookfn include/linux/netfilter.h:144 [inline]
 nf_hook_slow+0xbd/0x200 net/netfilter/core.c:626
 nf_hook include/linux/netfilter.h:259 [inline]
 NF_HOOK+0x23e/0x3e0 include/linux/netfilter.h:302
 __br_forward+0x433/0x610 net/bridge/br_forward.c:115
 deliver_clone net/bridge/br_forward.c:131 [inline]
 maybe_deliver+0xb5/0x150 net/bridge/br_forward.c:191
 br_flood+0x31b/0x670 net/bridge/br_forward.c:237
 br_handle_frame_finish+0x13c5/0x18f0 net/bridge/br_input.c:215
 br_nf_hook_thresh+0x3cd/0x4a0 net/bridge/br_netfilter_hooks.c:1184
 br_nf_pre_routing_finish_ipv6+0x9dc/0xd00 net/bridge/br_netfilter_ipv6.c:-1
 NF_HOOK include/linux/netfilter.h:304 [inline]
 br_nf_pre_routing_ipv6+0x349/0x6b0 net/bridge/br_netfilter_ipv6.c:184
 nf_hook_entry_hookfn include/linux/netfilter.h:144 [inline]
 nf_hook_bridge_pre net/bridge/br_input.c:277 [inline]
 br_handle_frame+0x1245/0x14d0 net/bridge/br_input.c:424
 __netif_receive_skb_core+0xfab/0x3af0 net/core/dev.c:5540
 __netif_receive_skb_one_core net/core/dev.c:5644 [inline]
 __netif_receive_skb+0x74/0x290 net/core/dev.c:5760
 process_backlog+0x391/0x6f0 net/core/dev.c:6088
 __napi_poll+0xc0/0x460 net/core/dev.c:6650
 napi_poll net/core/dev.c:6717 [inline]
 net_rx_action+0x616/0xc40 net/core/dev.c:6853
 handle_softirqs+0x280/0x820 kernel/softirq.c:578
 __do_softirq kernel/softirq.c:612 [inline]
 invoke_softirq kernel/softirq.c:452 [inline]
 __irq_exit_rcu+0xd3/0x190 kernel/softirq.c:661
 irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:_compound_head include/linux/page-flags.h:248 [inline]
RIP: 0010:virt_to_folio include/linux/mm.h:1291 [inline]
RIP: 0010:virt_to_slab mm/slab.h:218 [inline]
RIP: 0010:qlink_to_cache+0x1c/0xa0 mm/kasan/quarantine.c:129
Code: 41 5e 41 5f 5d e9 74 96 b0 08 0f 1f 40 00 e8 8b 30 5d ff 48 c1 e8 06 48 83 e0 c0 48 ba 00 00 00 00 00 ea ff ff 48 8b 4c 10 08 <f6> c1 01 75 76 48 01 d0 66 90 48 8b 48 08 f6 c1 01 75 3e 66 90 48
RSP: 0018:ffffc9000490efb8 EFLAGS: 00000202
RAX: 0000000000b3b180 RBX: ffffc9000490eff8 RCX: ffffea0000b3b001
RDX: ffffea0000000000 RSI: 000000000000d603 RDI: 000000000000d604
RBP: ffff88802cec6000 R08: 0000000000000001 R09: 0000000000000000
R10: ffff88802cec2000 R11: fffffbfff2238aa6 R12: 0000000000000000
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff88802cec6000
 qlist_free_all+0x39/0xd0 mm/kasan/quarantine.c:182
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6e/0x4b0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 __kmem_cache_alloc_node+0x13a/0x250 mm/slub.c:3534
 kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 is_state_visited kernel/bpf/verifier.c:16921 [inline]
 do_check+0x316b/0xdbf0 kernel/bpf/verifier.c:17092
 do_check_common+0xadb/0x13e0 kernel/bpf/verifier.c:19712
 do_check_main kernel/bpf/verifier.c:19775 [inline]
 bpf_check+0x658e/0xeba0 kernel/bpf/verifier.c:20443
 bpf_prog_load+0x1163/0x1670 kernel/bpf/syscall.c:2753
 __sys_bpf+0x5ba/0x890 kernel/bpf/syscall.c:5477
 __do_sys_bpf kernel/bpf/syscall.c:5581 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:5579 [inline]
 __x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5579
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f1a50f9c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f1a51e2d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007f1a51215fa0 RCX: 00007f1a50f9c819
RDX: 0000000000000094 RSI: 0000200000000440 RDI: 0000000000000005
RBP: 00007f1a51032c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1a51216038 R14: 00007f1a51215fa0 R15: 00007ffe466b8288
 </TASK>
net_ratelimit: 6467 callbacks suppressed
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:32:52:4c:a2:df:07, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:32:52:4c:a2:df:07, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
net_ratelimit: 8627 callbacks suppressed
bridge0: received packet on veth0_to_bridge with own address as source address (addr:ea:db:24:1a:33:5c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:32:52:4c:a2:df:07, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/04/12 11:43 linux-6.6.y 8cee53b8eaeb 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in kthreadd
2026/01/27 21:21 linux-6.6.y cbb31f77b879 9a514c2f .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in kthreadd
* Struck through repros no longer work on HEAD.