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)

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/26 23:26 android16-6.12 516976327553 a3c7249d .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in tun_free_netdev
* Struck through repros no longer work on HEAD.