INFO: rcu detected stall in NF_HOOK (4)

Status: upstream: reported syz repro on 2026/06/30 08:21
Reported-by: syzbot+02c2062b24a4563dd4bc@syzkaller.appspotmail.com
First crash: 44d, last: 34d
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2026/07/13 upstream (ToT) a13c140cc289 syz Didn't crash
▶ ▼ Similar bugs (8)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in NF_HOOK netfilter usb 1 syz, C error 13 769d 783d 0/29 closed as dup on 2024/06/20 17:29
linux-5.15 INFO: rcu detected stall in NF_HOOK 1 1 888d 888d 0/3 auto-obsoleted due to no activity on 2024/06/15 14:02
linux-6.6 INFO: rcu detected stall in NF_HOOK origin:upstream 1 syz, C error 16 23d 269d 0/2 upstream: reported C repro on 2025/11/16 12:13
linux-5.15 INFO: rcu detected stall in NF_HOOK (3) 1 2 568d 587d 0/3 auto-obsoleted due to no activity on 2025/05/01 22:51
linux-6.1 INFO: rcu detected stall in NF_HOOK origin:lts-only 1 syz unreliable 32 22d 799d 0/3 upstream: reported syz repro on 2024/06/04 14:31
upstream INFO: rcu detected stall in NF_HOOK (2) prio:normal netfilter 1 syz, C inconclusive error 144 9d22h 671d 0/29 upstream: reported C repro on 2024/10/10 12:45
linux-5.15 INFO: rcu detected stall in NF_HOOK (2) 1 1 771d 771d 0/3 auto-obsoleted due to no activity on 2024/10/11 06:09
android-54 BUG: soft lockup in NF_HOOK 1 1 791d 791d 0/2 auto-obsoleted due to no activity on 2024/09/10 19:37

Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
	(detected by 0, t=10502 jiffies, g=11797, q=1144)
rcu: All QSes seen, last rcu_preempt kthread activity 10496 (4294986868-4294976372), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10496 jiffies! g11797 f0x2 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:28176 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 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/0x11f0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
 kthread+0x42e/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 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 4705 Comm: syz.7.37 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:__lock_acquire+0x492/0x7b50 kernel/locking/lockdep.c:4950
Code: e8 03 48 89 84 24 b8 00 00 00 42 0f b6 04 00 84 c0 0f 85 3b 61 00 00 31 c0 48 89 9c 24 88 00 00 00 83 3b 00 0f 95 c0 41 09 c7 <41> c1 e7 0d 8b 84 24 98 00 00 00 c1 e0 0f 0f b7 c0 44 09 f8 8b 4c
RSP: 0018:ffffc90000dcfa60 EFLAGS: 00000006
RAX: 0000000000000001 RBX: ffff88807dd10ad4 RCX: 1ffff1100fba2176
RDX: 00000000000000bc RSI: 0000000000000000 RDI: ffff88807dd10ba0
RBP: ffffc90000dcfc90 R08: dffffc0000000000 R09: 0000000000000001
R10: dffffc0000000000 R11: fffffbfff1b15d5e R12: 0000000000000000
R13: ffff88807dd10000 R14: 00000000000000bc R15: 0000000000000003
FS:  00007f2d93bf96c0(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f80b6d58540 CR3: 0000000056458000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
 __raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
 _raw_spin_lock_irq+0xab/0xf0 kernel/locking/spinlock.c:170
 __run_hrtimer kernel/time/hrtimer.c:1689 [inline]
 __hrtimer_run_queues+0x59a/0xb60 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x397/0x8b0 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:check_preemption_disabled+0x0/0x110 lib/smp_processor_id.c:13
Code: 00 00 48 c7 c7 60 e9 32 8a e8 2c 01 00 00 65 ff 0d f1 2d 44 76 5b c3 00 00 cc 48 c7 c7 e0 29 7a 8a 48 c7 c6 20 2a 7a 8a eb 00 <55> 41 57 41 56 53 48 83 ec 10 65 48 8b 04 25 28 00 00 00 48 89 44
RSP: 0018:ffffc90000dd01d0 EFLAGS: 00000202
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffff88807dd10000
RDX: 0000000000000100 RSI: ffffffff8a7a2a20 RDI: ffffffff8a7a29e0
RBP: 1ffff11003ced215 R08: ffffc90000dd0500 R09: ffffc90000dd0510
R10: dffffc0000000000 R11: fffff520001ba06e R12: 0000000000000001
R13: 0000000000000003 R14: 1ffff11003ced216 R15: ffff88801e7690b7
 rcu_dynticks_curr_cpu_in_eqs kernel/rcu/tree.c:331 [inline]
 rcu_is_watching+0x11/0xa0 kernel/rcu/tree.c:1123
 rcu_read_lock_held_common kernel/rcu/update.c:108 [inline]
 rcu_read_lock_held+0x11/0x40 kernel/rcu/update.c:309
 __in6_dev_get include/net/addrconf.h:321 [inline]
 ip6_ignore_linkdown include/net/addrconf.h:412 [inline]
 find_match+0xf1/0xc20 net/ipv6/route.c:744
 __find_rr_leaf+0x240/0x750 net/ipv6/route.c:832
 find_rr_leaf net/ipv6/route.c:853 [inline]
 rt6_select net/ipv6/route.c:897 [inline]
 fib6_table_lookup+0x3c3/0xae0 net/ipv6/route.c:2184
 ip6_pol_route+0x21b/0x12d0 net/ipv6/route.c:2220
 pol_lookup_func include/net/ip6_fib.h:582 [inline]
 fib6_rule_lookup+0x222/0x5e0 net/ipv6/fib6_rules.c:115
 ip6_route_input_lookup net/ipv6/route.c:2290 [inline]
 ip6_route_input+0x77d/0xaa0 net/ipv6/route.c:2586
 ip6_rcv_finish+0x136/0x240 net/ipv6/ip6_input.c:77
 NF_HOOK+0x303/0x390 include/linux/netfilter.h:302
 __netif_receive_skb_one_core net/core/dev.c:5551 [inline]
 __netif_receive_skb+0xcc/0x290 net/core/dev.c:5665
 process_backlog+0x366/0x770 net/core/dev.c:6542
 __napi_poll+0xbb/0x430 net/core/dev.c:7101
 napi_poll net/core/dev.c:7168 [inline]
 net_rx_action+0x522/0xa80 net/core/dev.c:7258
 handle_softirqs+0x336/0x830 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:preempt_schedule_irq+0xb6/0x160 kernel/sched/core.c:6799
Code: 00 00 43 c6 44 37 04 f8 74 0b 0f 0b 48 f7 03 08 00 00 00 74 7f bf 01 00 00 00 e8 75 e5 8a f7 e8 20 b7 b7 f7 fb bf 01 00 00 00 <e8> d5 b5 ff ff 43 c6 44 37 08 00 48 c7 44 24 40 00 00 00 00 9c 8f
RSP: 0018:ffffc9000447f500 EFLAGS: 00000286
RAX: 475a1c902608ee00 RBX: 0000000000000000 RCX: 475a1c902608ee00
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: 0000000000000001
RBP: ffffc9000447f5b0 R08: ffffffff8f0fe048 R09: ffffffff8f0fe058
R10: ffffffff8f0fe050 R11: ffffffff8f0fe043 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff9200088fea0
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:__rcu_read_unlock+0x0/0xd0 kernel/rcu/tree_plugin.h:415
Code: c0 75 11 ff 03 8b 03 3d 00 00 00 40 7d 02 5b c3 0f 0b eb fa 89 d9 80 e1 07 80 c1 03 38 c1 7c e3 48 89 df e8 52 c5 58 00 eb d9 <41> 57 41 56 41 55 41 54 53 49 bf 00 00 00 00 00 fc ff df 65 48 8b
RSP: 0018:ffffc9000447f678 EFLAGS: 00000246
RAX: ffffffff81851300 RBX: 0000000000000000 RCX: ffff88807dd10000
RDX: 0000000000000000 RSI: ffffffff8a7a2a20 RDI: ffffffff8a7a29e0
RBP: 0000000000000000 R08: dffffc0000000000 R09: 1ffffffff203d218
R10: dffffc0000000000 R11: fffffbfff203d219 R12: dffffc0000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 rcu_read_unlock include/linux/rcupdate.h:772 [inline]
 is_bpf_text_address+0x24f/0x270 kernel/bpf/core.c:727
 kernel_text_address kernel/extable.c:151 [inline]
 __kernel_text_address+0x9a/0x100 kernel/extable.c:105
 unwind_get_return_address+0x49/0x80 arch/x86/kernel/unwind_orc.c:323
 arch_stack_walk+0xf2/0x140 arch/x86/kernel/stacktrace.c:26
 stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 tomoyo_realpath_from_path+0x5ad/0x5e0 security/tomoyo/realpath.c:291
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_number_perm+0x251/0x6b0 security/tomoyo/file.c:723
 security_file_ioctl+0x6c/0xa0 security/security.c:1556
 __do_sys_ioctl fs/ioctl.c:868 [inline]
 __se_sys_ioctl+0x48/0x170 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f2d94598e59
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:00007f2d93bf9028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f2d94820fa0 RCX: 00007f2d94598e59
RDX: 0000200000000080 RSI: 0000000000008946 RDI: 0000000000000006
RBP: 00007f2d9462ee6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2d94821038 R14: 00007f2d94820fa0 R15: 00007ffcd369afb8
 </TASK>

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/10 09:54 linux-5.15.y c86c4726e7f0 4167ee25 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in NF_HOOK
2026/07/01 01:34 linux-5.15.y eceeec79dbc6 00e8b0fd .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in NF_HOOK
2026/06/30 08:20 linux-5.15.y eceeec79dbc6 fff8d0a0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in NF_HOOK
* Struck through repros no longer work on HEAD.