[moderation] [batman?] BUG: soft lockup in neigh_timer_handler (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b4432656b36e Linux 6.15-rc4
git tree: bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=1783d374580000
kernel config: https://syzkaller.appspot.com/x/.config?x=714654674710be70
dashboard link: https://syzkaller.appspot.com/bug?extid=8e0c3a8bacb5690b8bad
compiler: Debian clang version 20.1.2 (++20250402124445+58df0ef89dd6-1~exp1~20250402004600.97), Debian LLD 20.1.2
CC: [ant...@mandelbit.com b.a.t...@lists.open-mesh.org da...@davemloft.net edum...@google.com ho...@kernel.org ku...@kernel.org linux-...@vger.kernel.org marek....@mailbox.org net...@vger.kernel.org pab...@redhat.com sv...@narfation.org s...@simonwunderlich.de]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f6e339019198/disk-b4432656.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/95a88f2fabf8/vmlinux-b4432656.xz
kernel image: https://storage.googleapis.com/syzbot-assets/10f5fd5829c7/bzImage-b4432656.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8e0c3a...@syzkaller.appspotmail.com

watchdog: BUG: soft lockup - CPU#0 stuck for 111s! [syz.3.433:9723]
Modules linked in:
irq event stamp: 19213245
hardirqs last enabled at (19213244): [<ffffffff8b55b3c4>] irqentry_exit+0x74/0x90 kernel/entry/common.c:357
hardirqs last disabled at (19213245): [<ffffffff8b559dbe>] sysvec_apic_timer_interrupt+0xe/0xc0 arch/x86/kernel/apic/apic.c:1049
softirqs last enabled at (18464978): [<ffffffff8185c3fa>] __do_softirq kernel/softirq.c:613 [inline]
softirqs last enabled at (18464978): [<ffffffff8185c3fa>] invoke_softirq kernel/softirq.c:453 [inline]
softirqs last enabled at (18464978): [<ffffffff8185c3fa>] __irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
softirqs last disabled at (18464981): [<ffffffff8185c3fa>] __do_softirq kernel/softirq.c:613 [inline]
softirqs last disabled at (18464981): [<ffffffff8185c3fa>] invoke_softirq kernel/softirq.c:453 [inline]
softirqs last disabled at (18464981): [<ffffffff8185c3fa>] __irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
CPU: 0 UID: 0 PID: 9723 Comm: syz.3.433 Not tainted 6.15.0-rc4-syzkaller-gb4432656b36e #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
RIP: 0010:memcpy_orig+0xc0/0x130 arch/x86/lib/memcpy_64.S:130
Code: 16 f0 4c 8b 5c 16 f8 4c 89 07 4c 89 4f 08 4c 89 54 17 f0 4c 89 5c 17 f8 c3 cc cc cc cc 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 <83> fa 08 72 1b 4c 8b 06 4c 8b 4c 16 f8 4c 89 07 4c 89 4c 17 f8 c3
RSP: 0018:ffffc90000006a78 EFLAGS: 00000283
RAX: ffffe8ffffcd6018 RBX: ffffe8ffffcd6000 RCX: ffffffff819d63aa
RDX: 000000000000000d RSI: ffffffff8b6bb960 RDI: ffffe8ffffcd6018
RBP: ffffc90000006b80 R08: ffffe8ffffcd6024 R09: 1ffffd1ffff9ac04
R10: dffffc0000000000 R11: fffff91ffff9ac05 R12: ffff8880b8832698
R13: 000000000000000e R14: 000000000000002c R15: dffffc0000000000
FS: 00007f40bbf586c0(0000) GS:ffff8881260cc000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b3335ffff CR3: 000000006d08a000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
do_perf_trace_lock include/trace/events/lock.h:50 [inline]
perf_trace_lock+0x28a/0x3b0 include/trace/events/lock.h:50
__do_trace_lock_release include/trace/events/lock.h:69 [inline]
trace_lock_release include/trace/events/lock.h:69 [inline]
lock_release+0x3b2/0x3e0 kernel/locking/lockdep.c:5877
rcu_lock_release include/linux/rcupdate.h:341 [inline]
rcu_read_unlock include/linux/rcupdate.h:871 [inline]
class_rcu_destructor include/linux/rcupdate.h:1155 [inline]
unwind_next_frame+0x19a9/0x2390 arch/x86/kernel/unwind_orc.c:680
arch_stack_walk+0x11c/0x150 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:247 [inline]
__kasan_slab_free+0x62/0x70 mm/kasan/common.c:264
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2398 [inline]
slab_free mm/slub.c:4656 [inline]
kmem_cache_free+0x192/0x3f0 mm/slub.c:4758
skb_kfree_head net/core/skbuff.c:1056 [inline]
skb_free_head net/core/skbuff.c:1070 [inline]
skb_release_data+0x670/0x890 net/core/skbuff.c:1097
skb_release_all net/core/skbuff.c:1162 [inline]
__kfree_skb net/core/skbuff.c:1176 [inline]
sk_skb_reason_drop+0x127/0x170 net/core/skbuff.c:1214
kfree_skb_reason include/linux/skbuff.h:1279 [inline]
kfree_skb include/linux/skbuff.h:1288 [inline]
batadv_interface_tx+0x598/0x14c0 net/batman-adv/mesh-interface.c:390
__netdev_start_xmit include/linux/netdevice.h:5203 [inline]
netdev_start_xmit include/linux/netdevice.h:5212 [inline]
xmit_one net/core/dev.c:3776 [inline]
dev_hard_start_xmit+0x2ff/0x880 net/core/dev.c:3792
__dev_queue_xmit+0x1adf/0x3a70 net/core/dev.c:4629
dev_queue_xmit include/linux/netdevice.h:3350 [inline]
neigh_hh_output include/net/neighbour.h:523 [inline]
neigh_output include/net/neighbour.h:537 [inline]
ip6_finish_output2+0x11bc/0x16a0 net/ipv6/ip6_output.c:141
__ip6_finish_output net/ipv6/ip6_output.c:-1 [inline]
ip6_finish_output+0x234/0x7d0 net/ipv6/ip6_output.c:226
NF_HOOK include/linux/netfilter.h:314 [inline]
ndisc_send_skb+0xb47/0x1400 net/ipv6/ndisc.c:513
ndisc_send_ns net/ipv6/ndisc.c:671 [inline]
ndisc_solicit+0x444/0x610 net/ipv6/ndisc.c:-1
neigh_probe net/core/neighbour.c:1024 [inline]
neigh_timer_handler+0xaaf/0x1030 net/core/neighbour.c:1106
call_timer_fn+0x17b/0x5f0 kernel/time/timer.c:1789
expire_timers kernel/time/timer.c:1840 [inline]
__run_timers kernel/time/timer.c:2414 [inline]
__run_timer_base+0x61a/0x860 kernel/time/timer.c:2426
run_timer_base kernel/time/timer.c:2435 [inline]
run_timer_softirq+0xb7/0x180 kernel/time/timer.c:2445
handle_softirqs+0x283/0x870 kernel/softirq.c:579
__do_softirq kernel/softirq.c:613 [inline]
invoke_softirq kernel/softirq.c:453 [inline]
__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
instr_sysvec_irq_work arch/x86/kernel/irq_work.c:17 [inline]
sysvec_irq_work+0xa3/0xc0 arch/x86/kernel/irq_work.c:17
</IRQ>
<TASK>
asm_sysvec_irq_work+0x1a/0x20 arch/x86/include/asm/idtentry.h:738
RIP: 0010:finish_task_switch+0x26b/0x950 kernel/sched/core.c:5250
Code: 0f 84 3c 01 00 00 48 85 db 0f 85 63 01 00 00 0f 1f 44 00 00 4c 8b 75 d0 4c 89 e7 e8 ff 53 c6 09 e8 6a 66 35 00 fb 4c 8b 65 c0 <49> 8d bc 24 18 16 00 00 48 89 f8 48 c1 e8 03 42 0f b6 04 28 84 c0
RSP: 0018:ffffc90003e36d38 EFLAGS: 00000282
RAX: 1900209162f18200 RBX: 0000000000000000 RCX: 1900209162f18200
RDX: 0000000000000000 RSI: ffffffff8d748fd1 RDI: ffffffff8bc1cde0
RBP: ffffc90003e36d90 R08: ffffffff8f7ec977 R09: 1ffffffff1efd92e
R10: dffffc0000000000 R11: fffffbfff1efd92f R12: ffff8880616e8000
R13: dffffc0000000000 R14: ffff88802684bc00 R15: ffff8880b883a6d8
context_switch kernel/sched/core.c:5385 [inline]
__schedule+0x16ea/0x4cd0 kernel/sched/core.c:6767
preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7090
irqentry_exit+0x6f/0x90 kernel/entry/common.c:354
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:_raw_spin_unlock_irqrestore+0xd7/0x110 kernel/locking/spinlock.c:195
Code: 65 8b 05 5c 15 1d 07 85 c0 74 40 48 c7 04 24 0e 36 e0 45 4b c7 04 27 00 00 00 00 65 48 8b 05 30 15 1d 07 48 3b 44 24 48 75 28 <48> 8d 65 e0 5b 41 5c 41 5e 41 5f 5d c3 cc cc cc cc cc e8 82 7c fd
RSP: 0018:ffffc90003e37120 EFLAGS: 00000246
RAX: 1900209162f18200 RBX: 0000000000000a06 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8d748fd1 RDI: 00000000ffffffff
RBP: ffffc90003e371b0 R08: ffffffff8f7ec977 R09: 1ffffffff1efd92e
R10: dffffc0000000000 R11: fffffbfff1efd92f R12: dffffc0000000000
R13: ffff888033f24fc0 R14: ffffffff99a33a30 R15: 1ffff920007c6e24
__debug_check_no_obj_freed lib/debugobjects.c:1108 [inline]
debug_check_no_obj_freed+0x451/0x470 lib/debugobjects.c:1129
slab_free_hook mm/slub.c:2329 [inline]
slab_free mm/slub.c:4656 [inline]
kfree+0x117/0x440 mm/slub.c:4855
pop_stack+0x35b/0x470 kernel/bpf/verifier.c:2011
do_check_common+0x16fd/0x20b0 kernel/bpf/verifier.c:22785
do_check_main kernel/bpf/verifier.c:22867 [inline]
bpf_check+0x13679/0x19a70 kernel/bpf/verifier.c:24033
bpf_prog_load+0x1318/0x1930 kernel/bpf/syscall.c:2971
__sys_bpf+0x5f1/0x860 kernel/bpf/syscall.c:5834
__do_sys_bpf kernel/bpf/syscall.c:5941 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5939 [inline]
__x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5939
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xf6/0x210 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f40bb18e969
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f40bbf58038 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007f40bb3b6080 RCX: 00007f40bb18e969
RDX: 0000000000000048 RSI: 00002000000054c0 RDI: 0000000000000005
RBP: 00007f40bb210ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f40bb3b6080 R15: 00007fffbe65cb88
</TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 31 Comm: khungtaskd Not tainted 6.15.0-rc4-syzkaller-gb4432656b36e #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
RIP: 0010:io_serial_in+0x77/0xc0 drivers/tty/serial/8250/8250_port.c:409
Code: e8 1e 40 82 fc 44 89 f9 d3 e3 49 83 c6 40 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 74 08 4c 89 f7 e8 ff 34 e4 fc 41 03 1e 89 da ec <0f> b6 c0 5b 41 5c 41 5e 41 5f c3 cc cc cc cc cc 44 89 f9 80 e1 07
RSP: 0018:ffffc90000a87778 EFLAGS: 00000006
RAX: 1ffffffff3369705 RBX: 00000000000003f9 RCX: 0000000000000000
RDX: 00000000000003f9 RSI: 0000000000000000 RDI: 0000000000000020
RBP: ffffc90000a87950 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: ffffffff853d7e60 R12: dffffc0000000000
R13: dffffc0000000000 R14: ffffffff99b4bbc0 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8881261cc000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f2ef5ab3580 CR3: 00000000765e0000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<TASK>
serial_port_in include/linux/serial_core.h:791 [inline]
serial8250_console_write+0x581/0x1ba0 drivers/tty/serial/8250/8250_port.c:3420
console_emit_next_record kernel/printk/printk.c:3138 [inline]
console_flush_all+0x725/0xc40 kernel/printk/printk.c:3226
__console_flush_and_unlock kernel/printk/printk.c:3285 [inline]
console_unlock+0xc4/0x270 kernel/printk/printk.c:3325
vprintk_emit+0x5b7/0x7a0 kernel/printk/printk.c:2450
_printk+0xcf/0x120 kernel/printk/printk.c:2475
check_hung_task kernel/hung_task.c:181 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:265 [inline]
watchdog+0xb4f/0x1030 kernel/hung_task.c:437
kthread+0x70e/0x8a0 kernel/kthread.c:464
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.