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: 225d, last: 2d04h
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 319d 456d 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 787d 787d 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 682d 792d 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 253d 253d 0/3 auto-obsoleted due to no activity on 2026/04/19 19:10

Sample crash report:
INFO: task kworker/1:1:45 blocked for more than 122 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:45    tgid:45    ppid:2      flags:0x00004000
Workqueue: events fqdir_free_fn
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:6063 [inline]
 __schedule+0x1496/0x20b0 kernel/sched/core.c:7883
 __schedule_loop kernel/sched/core.c:7960 [inline]
 schedule+0xc5/0x240 kernel/sched/core.c:7975
 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+0x368/0x650 kernel/sched/completion.c:127
 wait_for_completion+0x1c/0x40 kernel/sched/completion.c:148
 rcu_barrier+0x45a/0x580 kernel/rcu/tree.c:4657
 fqdir_free_fn+0x36/0x150 net/ipv4/inet_fragment.c:167
 process_one_work kernel/workqueue.c:3273 [inline]
 process_scheduled_works+0x7f4/0x1060 kernel/workqueue.c:3354
 worker_thread+0xc99/0x13f0 kernel/workqueue.c:3435
 kthread+0x2c4/0x360 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.0.945:3240 blocked for more than 124 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.945       state:D stack:0     pid:3240  tgid:3240  ppid:299    flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:6063 [inline]
 __schedule+0x1496/0x20b0 kernel/sched/core.c:7883
 __schedule_loop kernel/sched/core.c:7960 [inline]
 schedule+0xc5/0x240 kernel/sched/core.c:7975
 schedule_preempt_disabled+0x14/0x30 kernel/sched/core.c:8032
 __mutex_lock_common kernel/locking/mutex.c:707 [inline]
 __mutex_lock+0x902/0x1b90 kernel/locking/mutex.c:806
 __mutex_lock_slowpath+0xe/0x20 kernel/locking/mutex.c:1136
 mutex_lock+0x113/0x1d0 kernel/locking/mutex.c:285
 rcu_barrier+0x4d/0x580 kernel/rcu/tree.c:4589
 kvm_mmu_uninit_tdp_mmu+0x1ea/0x210 arch/x86/kvm/mmu/tdp_mmu.c:51
 kvm_mmu_uninit_vm+0x27/0x60 arch/x86/kvm/mmu/mmu.c:6569
 kvm_arch_destroy_vm+0x395/0x410 arch/x86/kvm/x86.c:13008
 kvm_destroy_vm virt/kvm/kvm_main.c:1355 [inline]
 kvm_put_kvm+0xadf/0x12d0 virt/kvm/kvm_main.c:1392
 kvm_vm_release+0x47/0x70 virt/kvm/kvm_main.c:1415
 __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
 resume_user_mode_work+0x35/0x50 include/linux/resume_user_mode.h:50
 exit_to_user_mode_loop kernel/entry/common.c:114 [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+0x63/0xb0 kernel/entry/common.c:218
 do_syscall_64+0x63/0xf0 arch/x86/entry/common.c:84
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fd3da59e159
RSP: 002b:00007fff0a244a78 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007fd3da827da0 RCX: 00007fd3da59e159
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007fd3da827da0 R08: 0000000000000006 R09: 0000000000000000
R10: 00000000003ffbd8 R11: 0000000000000246 R12: 00000000000267eb
R13: 00007fd3da82609c R14: 00000000000265b0 R15: 00007fd3da826090
 </TASK>
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 37 Comm: khungtaskd Not tainted syzkaller #0 249ace596eef83e7ab94f4ef92c49a820648daf1
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+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 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 30 Comm: ksoftirqd/1 Not tainted syzkaller #0 249ace596eef83e7ab94f4ef92c49a820648daf1
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:update_stack_state+0x4e/0x4d0 arch/x86/kernel/unwind_frame.c:205
Code: 48 89 f8 48 c1 e8 03 48 89 45 c0 42 0f b6 04 38 84 c0 0f 85 1e 04 00 00 41 8b 45 00 89 45 b4 49 8d 7d 58 48 89 f8 48 c1 e8 03 <48> 89 45 a0 42 80 3c 38 00 74 09 e8 12 c6 9b 00 49 8d 7d 58 48 8b
RSP: 0018:ffffc900001f6d88 EFLAGS: 00000a02
RAX: 1ffff9200003ede0 RBX: ffffc900001f6ea8 RCX: ffffc900001f75b0
RDX: dffffc0000000000 RSI: ffffc900001f75b0 RDI: ffffc900001f6f00
RBP: ffffc900001f6e38 R08: ffffc900001f6f70 R09: ffffc900001f6f68
R10: 000000000000000a R11: ffffffff8175a7a0 R12: ffffc900001f74b0
R13: ffffc900001f6ea8 R14: ffffc900001f75b0 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8881f6f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000559c09f13af8 CR3: 000000010c7c4000 CR4: 00000000003526b0
Call Trace:
 <TASK>
 unwind_next_frame+0x39e/0x6b0 arch/x86/kernel/unwind_frame.c:315
 arch_stack_walk+0x138/0x170 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xaa/0x100 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:49 [inline]
 kasan_save_track+0x3e/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
 consume_skb+0x65/0x1a0 net/core/skbuff.c:1436
 netlink_broadcast_filtered+0x10c2/0x11d0 net/netlink/af_netlink.c:1531
 nlmsg_multicast_filtered include/net/netlink.h:1125 [inline]
 nlmsg_multicast include/net/netlink.h:1144 [inline]
 nlmsg_notify+0xed/0x1b0 net/netlink/af_netlink.c:2592
 rtnl_notify+0x9e/0xd0 net/core/rtnetlink.c:789
 fdb_notify+0xce/0x150 net/bridge/br_fdb.c:206
 br_fdb_update+0x5b7/0x6c0 net/bridge/br_fdb.c:951
 br_handle_frame_finish+0x385/0x1620 net/bridge/br_input.c:141
 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+0xfc4/0x3a70 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+0xcd/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
 run_ksoftirqd+0x20/0x30 kernel/softirq.c:999
 smpboot_thread_fn+0x486/0x8b0 kernel/smpboot.c:164
 kthread+0x2c4/0x360 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: 372309 callbacks suppressed
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:3a:b0:3b:07:c7:ce, 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:3a:b0:3b:07:c7:ce, 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:3a:b0:3b:07:c7:ce, 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:3a:b0:3b:07:c7:ce, 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:3a:b0:3b:07:c7:ce, vlan:0)

Crashes (24):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/18 12:18 android16-6.12 17176090d7cd 853b104b .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/09/15 17:46 android16-6.12 5c165027e17c 2daa4bb5 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/09/14 09:38 android16-6.12 8eff909dd82d 70a60e12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/07/17 02:50 android16-6.12 57c0ba8fb2f8 71b49442 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/07/03 10:51 android16-6.12 d36feda1de57 58bf2096 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/06/21 20:40 android16-6.12 8f68185b8289 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/06/21 13:51 android16-6.12 8f68185b8289 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/06/18 00:53 android16-6.12 8f68185b8289 b62b3ded .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/06/02 15:57 android16-6.12 be0db38c7358 62fe1528 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/05/28 22:58 android16-6.12 ca09f536934e 681715f7 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/05/22 18:09 android16-6.12 9d40b257ba08 5f091fcc .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/05/05 12:07 android16-6.12 fc365114731f 06e69a27 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/04/26 18:01 android16-6.12 1cbb81cdf8fc 9c2d0995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/04/18 11:32 android16-6.12 6532ca3bb1f7 303e2802 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/03/07 11:10 android16-6.12 792a289062b8 5cb44a80 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
2026/03/04 06:10 android16-6.12 c146faa1afa9 4180d919 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust INFO: task hung in fqdir_free_fn
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.