syzbot


INFO: task hung in fqdir_free_fn (2)

Status: premoderation: reported on 2026/02/07 13:12
Reported-by: syzbot+536980ef52d8f82cfa08@syzkaller.appspotmail.com
First crash: 23d, last: 1d06h
Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-6-12 INFO: task hung in fqdir_free_fn 1 32 117d 254d 0/1 auto-obsoleted due to no activity on 2026/01/05 06:30
linux-5.15 INFO: task hung in fqdir_free_fn 1 1 586d 586d 0/3 auto-obsoleted due to no activity on 2024/11/01 18:36
upstream INFO: task hung in fqdir_free_fn net 1 4 480d 590d 0/29 auto-obsoleted due to no activity on 2025/02/05 05:14
linux-5.15 INFO: task hung in fqdir_free_fn (2) 1 1 52d 52d 0/3 upstream: reported on 2026/01/09 19:10

Sample crash report:
INFO: task kworker/1:1:46 blocked for more than 123 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/1:1     state:D stack:0     pid:46    tgid:46    ppid:2      flags:0x00004000
Workqueue: events fqdir_free_fn
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:6016 [inline]
 __schedule+0x134f/0x1ea0 kernel/sched/core.c:7864
 __schedule_loop kernel/sched/core.c:7945 [inline]
 schedule+0xc5/0x240 kernel/sched/core.c:7960
 schedule_timeout+0xc7/0x3b0 kernel/time/timer.c:2596
 do_wait_for_common kernel/sched/completion.c:95 [inline]
 __wait_for_common kernel/sched/completion.c:116 [inline]
 wait_for_common+0x369/0x650 kernel/sched/completion.c:127
 wait_for_completion+0x1c/0x40 kernel/sched/completion.c:148
 rcu_barrier+0x415/0x540 kernel/rcu/tree.c:4657
 fqdir_free_fn+0x36/0x150 net/ipv4/inet_fragment.c:167
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0x7d4/0x1020 kernel/workqueue.c:3319
 worker_thread+0xc70/0x10b0 kernel/workqueue.c:3400
 kthread+0x2c9/0x370 kernel/kthread.c:389
 ret_from_fork+0x64/0xa0 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
INFO: task syz.8.1405:4828 blocked for more than 124 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.8.1405      state:D stack:0     pid:4828  tgid:4827  ppid:4350   flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:6016 [inline]
 __schedule+0x134f/0x1ea0 kernel/sched/core.c:7864
 __schedule_loop kernel/sched/core.c:7945 [inline]
 schedule+0xc5/0x240 kernel/sched/core.c:7960
 schedule_timeout+0xc7/0x3b0 kernel/time/timer.c:2596
 do_wait_for_common kernel/sched/completion.c:95 [inline]
 __wait_for_common kernel/sched/completion.c:116 [inline]
 wait_for_common+0x369/0x650 kernel/sched/completion.c:127
 wait_for_completion+0x1c/0x40 kernel/sched/completion.c:148
 exit_aio+0x2ec/0x3c0 fs/aio.c:927
 __mmput+0x30/0x320 kernel/fork.c:1350
 mmput+0x55/0x170 kernel/fork.c:1376
 exit_mm kernel/exit.c:574 [inline]
 do_exit+0x93f/0x2650 kernel/exit.c:940
 do_group_exit+0x229/0x2f0 kernel/exit.c:1095
 get_signal+0x1398/0x14e0 kernel/signal.c:2933
 arch_do_signal_or_restart+0xbc/0x760 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: 0033:0x7f7825d9c42b
RSP: 002b:00007f7826bf9f00 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: fffffffffffffffc RBX: 0000000000000007 RCX: 00007f7825d9c42b
RDX: 00007f7826bf9fc0 RSI: 0000000040085503 RDI: 0000000000000007
RBP: 00007f7826bfafd0 R08: 00007f7825c644e7 R09: 00007f7826bf9fc8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000080085502
R13: 0000000800000000 R14: 0000000000000008 R15: 00007f7825e50bf4
 </TASK>
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 37 Comm: khungtaskd Not tainted syzkaller #0 c4f231820317ff22bb61fe038e0df9024df7047c
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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:113
 nmi_trigger_cpumask_backtrace+0x142/0x2c0 lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:41
 trigger_all_cpu_backtrace include/linux/nmi.h:158 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:267 [inline]
 watchdog+0xdad/0xf00 kernel/hung_task.c:423
 kthread+0x2c9/0x370 kernel/kthread.c:389
 ret_from_fork+0x64/0xa0 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: 33 Comm: rcuop/1 Not tainted syzkaller #0 c4f231820317ff22bb61fe038e0df9024df7047c
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:__rcu_read_lock+0x5/0x60 kernel/rcu/tree_plugin.h:413
Code: 99 ff e9 5c fb ff ff 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 b8 90 87 9a 2f 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 55 <48> 89 e5 53 65 48 8b 1d 9f 81 94 7e 48 81 c3 c4 04 00 00 48 89 d8
RSP: 0018:ffffc90000007128 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffff8881b7518930 RCX: ffff88810367df00
RDX: 0000000000000100 RSI: ffff88811c080000 RDI: ffff8881b75188c0
RBP: ffffc900000071c0 R08: ffff88810367df00 R09: 0000000000000002
R10: 0000000000000000 R11: ffffffff8374eae0 R12: dffffc0000000000
R13: 0000000000000046 R14: ffff8881b75188c0 R15: ffff88811c080ac0
FS:  0000000000000000(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa5f5d47e20 CR3: 000000010c742000 CR4: 00000000003526b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: fffffffffffffffc DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 __netdev_start_xmit include/linux/netdevice.h:4975 [inline]
 netdev_start_xmit include/linux/netdevice.h:4984 [inline]
 xmit_one net/core/dev.c:3681 [inline]
 dev_hard_start_xmit+0x21b/0x760 net/core/dev.c:3697
 __dev_queue_xmit+0x1905/0x3690 net/core/dev.c:4533
 dev_queue_xmit include/linux/netdevice.h:3141 [inline]
 br_dev_queue_push_xmit+0x55c/0x700 net/bridge/br_forward.c:53
 NF_HOOK include/linux/netfilter.h:317 [inline]
 br_forward_finish net/bridge/br_forward.c:66 [inline]
 NF_HOOK include/linux/netfilter.h:317 [inline]
 __br_forward+0x25c/0x390 net/bridge/br_forward.c:115
 deliver_clone net/bridge/br_forward.c:131 [inline]
 br_flood+0x67e/0x730 net/bridge/br_forward.c:246
 br_handle_frame_finish+0x12f9/0x1760 net/bridge/br_input.c:215
 nf_hook_bridge_pre net/bridge/br_input.c:301 [inline]
 br_handle_frame+0x5a6/0xba0 net/bridge/br_input.c:424
 __netif_receive_skb_core+0xfae/0x3ab0 net/core/dev.c:5670
 __netif_receive_skb_one_core net/core/dev.c:5774 [inline]
 __netif_receive_skb net/core/dev.c:5889 [inline]
 process_backlog+0x3e5/0xad0 net/core/dev.c:6225
 __napi_poll+0xd0/0x610 net/core/dev.c:6876
 napi_poll net/core/dev.c:6945 [inline]
 net_rx_action+0x5ea/0xd80 net/core/dev.c:7067
 handle_softirqs+0x1aa/0x630 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+0x5d9/0xd40 kernel/rcu/tree.c:2594
 nocb_cb_wait kernel/rcu/tree_nocb.h:923 [inline]
 rcu_nocb_cb_kthread+0x524/0xb30 kernel/rcu/tree_nocb.h:957
 kthread+0x2c9/0x370 kernel/kthread.c:389
 ret_from_fork+0x64/0xa0 arch/x86/kernel/process.c:153
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
net_ratelimit: 195794 callbacks suppressed
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
net_ratelimit: 241010 callbacks suppressed
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:1c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_1 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth1_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)

Crashes (8):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/01 13:53 android16-6.12 7de305bfa436 43249bac .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/02/28 16:08 android16-6.12 7de305bfa436 43249bac .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/02/23 21:50 android16-6.12 c42c886c1098 6beca497 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/02/23 19:10 android16-6.12 c42c886c1098 6beca497 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/02/23 16:56 android16-6.12 c42c886c1098 6beca497 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/02/21 19:03 android16-6.12 7712ca595283 6e7b5511 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/02/12 22:06 android16-6.12 7b84a1af9194 504cb1bf .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/02/07 13:12 android16-6.12 6aeca23b5dee f20fc9f9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
* Struck through repros no longer work on HEAD.