syzbot
INFO: task hung in tun_free_netdev
Status:
premoderation: reported on 2026/09/26 23:27
Reported-by: syzbot+0af59bbd52df7f2d53fa@syzkaller.appspotmail.com
First crash: 13d, last: 13d
Sample crash report:
INFO: task syz-executor:293 blocked for more than 122 seconds.
Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor state:R running task stack:0 pid:293 tgid:293 ppid:1 flags:0x00004006
Call Trace:
<TASK>
context_switch kernel/sched/core.c:6063 [inline]
__schedule+0x1496/0x20b0 kernel/sched/core.c:7883
preempt_schedule_common+0x2d/0x60 kernel/sched/core.c:8062
preempt_schedule+0xc5/0xe0 kernel/sched/core.c:8086
preempt_schedule_thunk+0x1a/0x40 arch/x86/entry/thunk.S:12
__local_bh_enable_ip+0x64/0x80 kernel/softirq.c:437
__raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline]
_raw_spin_unlock_bh+0x54/0x60 kernel/locking/spinlock.c:210
spin_unlock_bh include/linux/spinlock.h:396 [inline]
__tun_set_ebpf drivers/net/tun.c:2310 [inline]
tun_free_netdev+0x154/0x190 drivers/net/tun.c:2327
netdev_run_todo+0xb12/0xce0 net/core/dev.c:10939
rtnl_unlock+0x12/0x20 net/core/rtnetlink.c:152
tun_detach drivers/net/tun.c:704 [inline]
tun_chr_close+0xc5/0x150 drivers/net/tun.c:3523
__fput+0x20b/0xa30 fs/file_table.c:447
____fput+0x20/0x30 fs/file_table.c:475
task_work_run+0x1e5/0x260 kernel/task_work.c:246
exit_task_work include/linux/task_work.h:43 [inline]
do_exit+0xa46/0x2850 kernel/exit.c:961
do_group_exit+0x21f/0x2f0 kernel/exit.c:1104
get_signal+0x134c/0x1490 kernel/signal.c:2941
arch_do_signal_or_restart+0xbc/0x700 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop kernel/entry/common.c:111 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x57/0xb0 kernel/entry/common.c:218
do_syscall_64+0x63/0xf0 arch/x86/entry/common.c:84
entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fb9e119f99a
RSP: 002b:00007ffca2336d38 EFLAGS: 00000202 ORIG_RAX: 0000000000000036
RAX: 0000000000000000 RBX: 00007ffca2336dc0 RCX: 00007fb9e119f99a
RDX: 0000000000000040 RSI: 0000000000000029 RDI: 0000000000000003
RBP: 0000000000000003 R08: 00000000000002e8 R09: 0000000000000000
R10: 00007fb9e13ef2a0 R11: 0000000000000202 R12: 00007fb9e13ef240
R13: 00007ffca2336d5c R14: 0000000000000000 R15: 00007fb9e13effc0
</TASK>
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 37 Comm: khungtaskd Not tainted syzkaller #0 f6ed0fb9bb938319f6518c785cf37c2d863a58c7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
<TASK>
__dump_stack+0x21/0x30 lib/dump_stack.c:94
dump_stack_lvl+0x140/0x1c0 lib/dump_stack.c:120
dump_stack+0x19/0x20 lib/dump_stack.c:129
nmi_cpu_backtrace+0x2ba/0x2d0 lib/nmi_backtrace.c:114
nmi_trigger_cpumask_backtrace+0x142/0x2c0 lib/nmi_backtrace.c:63
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:41
cpumask_backtrace+0x1f/0x30 lib/nmi_backtrace.c:127
trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:267 [inline]
watchdog+0xe45/0xf90 kernel/hung_task.c:423
kthread+0x2c4/0x360 kernel/kthread.c:389
ret_from_fork+0x67/0xa0 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 20 Comm: rcuop/0 Not tainted syzkaller #0 f6ed0fb9bb938319f6518c785cf37c2d863a58c7
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:filter_irq_stacks+0x70/0xa0 kernel/stacktrace.c:397
Code: 30 02 c0 85 0f 93 c1 48 3d 90 17 c0 85 0f 92 c2 84 d1 75 27 48 3d 40 b5 a7 85 0f 92 c1 48 3d 66 b5 a7 85 0f 93 c0 08 c8 74 11 <48> ff c3 49 83 c7 08 49 39 dc 75 ae 44 89 e3 eb 06 ff c3 eb 02 31
RSP: 0018:ffffc90000007058 EFLAGS: 00000202
RAX: ffffffff8484f801 RBX: 000000000000000d RCX: 0000000000000001
RDX: 0000000000000001 RSI: 000000000000001a RDI: ffffc90000007100
RBP: ffffc90000007080 R08: ffffc90000007090 R09: ffffc90000007088
R10: 0000000000000019 R11: ffffffff8175a6a0 R12: 000000000000001a
R13: dffffc0000000000 R14: ffffc90000007100 R15: ffffc90000007168
FS: 0000000000000000(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7287ff84c0 CR3: 000000010cf8e000 CR4: 00000000003526b0
Call Trace:
<IRQ>
stack_depot_save_flags+0x38/0x800 lib/stackdepot.c:609
kasan_save_stack mm/kasan/common.c:50 [inline]
kasan_save_track+0x4f/0x80 mm/kasan/common.c:70
kasan_save_free_info+0x44/0x50 mm/kasan/generic.c:579
poison_slab_object mm/kasan/common.c:249 [inline]
__kasan_slab_free+0x5f/0x80 mm/kasan/common.c:266
kasan_slab_free include/linux/kasan.h:234 [inline]
slab_free_hook mm/slub.c:2445 [inline]
slab_free mm/slub.c:4714 [inline]
kmem_cache_free+0x1bd/0x4f0 mm/slub.c:4825
kfree_skbmem net/core/skbuff.c:-1 [inline]
__kfree_skb+0x18f/0x210 net/core/skbuff.c:1205
sk_skb_reason_drop+0xd8/0x310 net/core/skbuff.c:1242
kfree_skb_reason include/linux/skbuff.h:1303 [inline]
kfree_skb include/linux/skbuff.h:1312 [inline]
ip6_mc_input+0x433/0x680 net/ipv6/ip6_input.c:587
dst_input include/net/dst.h:469 [inline]
ip6_rcv_finish+0x344/0x3c0 net/ipv6/ip6_input.c:79
NF_HOOK include/linux/netfilter.h:317 [inline]
ipv6_rcv+0xf1/0x240 net/ipv6/ip6_input.c:309
__netif_receive_skb_one_core net/core/dev.c:5801 [inline]
__netif_receive_skb net/core/dev.c:5914 [inline]
netif_receive_skb_internal net/core/dev.c:6000 [inline]
netif_receive_skb+0x146/0x7b0 net/core/dev.c:6059
br_netif_receive_skb net/bridge/br_input.c:30 [inline]
NF_HOOK include/linux/netfilter.h:317 [inline]
br_pass_frame_up+0x126/0x1b0 net/bridge/br_input.c:70
br_handle_frame_finish+0x1178/0x1620 net/bridge/br_input.c:-1
nf_hook_bridge_pre net/bridge/br_input.c:301 [inline]
br_handle_frame+0x5a5/0xba0 net/bridge/br_input.c:424
__netif_receive_skb_core+0xfc1/0x3a70 net/core/dev.c:5695
__netif_receive_skb_one_core net/core/dev.c:5799 [inline]
__netif_receive_skb net/core/dev.c:5914 [inline]
process_backlog+0x40b/0xaf0 net/core/dev.c:6250
__napi_poll+0xd0/0x600 net/core/dev.c:6901
napi_poll net/core/dev.c:6970 [inline]
net_rx_action+0x5dc/0xd70 net/core/dev.c:7092
handle_softirqs+0x1aa/0x620 kernel/softirq.c:621
__do_softirq+0xf/0x16 kernel/softirq.c:659
do_softirq+0xb8/0x110 kernel/softirq.c:503
</IRQ>
<TASK>
__local_bh_enable_ip+0x74/0x80 kernel/softirq.c:430
local_bh_enable include/linux/bottom_half.h:33 [inline]
rcu_do_batch+0x590/0xcb0 kernel/rcu/tree.c:2594
nocb_cb_wait kernel/rcu/tree_nocb.h:923 [inline]
rcu_nocb_cb_kthread+0x533/0xb60 kernel/rcu/tree_nocb.h:957
kthread+0x2c4/0x360 kernel/kthread.c:389
ret_from_fork+0x67/0xa0 arch/x86/kernel/process.c:153
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>
net_ratelimit: 95162 callbacks suppressed
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 bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, 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 veth0_to_bridge with own address as source address (addr:7e:e1:ed:ae:de:61, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:7e:e1:ed:ae:de:61, 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:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
* Struck through repros no longer work on HEAD.