syzbot


INFO: task hung in ret_from_fork (4)

Status: upstream: reported C repro on 2026/03/01 18:35
Subsystems: kernel
[Documentation on labels]
Reported-by: syzbot+7c11975a7e4a2735d529@syzkaller.appspotmail.com
First crash: 648d, last: 9d15h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
0b557ed3-545c-4da0-bc88-421586d42528 patching 💥 INFO: task hung in ret_from_fork (4) 2026/03/02 10:20 2026/03/02 10:20 2026/03/02 10:31 305c0ec5cd886e2d13738e28e1b2df9b0ec20fc9 reproducer did not crash
Cause bisection: failed (error log, bisect log)
  
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [kernel?] INFO: task hung in ret_from_fork (4) 0 (1) 2026/03/01 18:35
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in ret_from_fork (3) serial 1 1 848d 848d 0/29 auto-obsoleted due to no activity on 2024/02/08 01:02
upstream INFO: task hung in ret_from_fork (2) fs 1 1 1951d 1951d 0/29 auto-closed as invalid on 2020/12/31 10:28
upstream INFO: task hung in ret_from_fork fs 1 4 2766d 2772d 0/29 auto-closed as invalid on 2019/02/22 10:29

Sample crash report:
INFO: task kworker/1:8:5970 blocked for more than 159 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/1:8     state:D stack:30744 pid:5970  tgid:5970  ppid:2      task_flags:0x4208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5295 [inline]
 __schedule+0x1585/0x5340 kernel/sched/core.c:6907
 __schedule_loop kernel/sched/core.c:6989 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7004
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7061
 kthread+0x260/0x470 kernel/kthread.c:451
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Showing all locks held in the system:
2 locks held by kworker/0:0/9:
1 lock held by kworker/0:1/10:
 #0: ffffffff8e5fec68 (wq_pool_attach_mutex){+.+.}-{4:4}, at: worker_attach_to_pool+0x2e/0x3a0 kernel/workqueue.c:2691
2 locks held by kworker/u8:0/12:
2 locks held by kworker/u8:1/13:
1 lock held by kworker/R-mm_pe/14:
 #0: ffffffff8e5fec68 (wq_pool_attach_mutex){+.+.}-{4:4}, at: worker_detach_from_pool kernel/workqueue.c:2749 [inline]
 #0: ffffffff8e5fec68 (wq_pool_attach_mutex){+.+.}-{4:4}, at: rescuer_thread+0xc4a/0x1120 kernel/workqueue.c:3610
3 locks held by kworker/1:0/24:
 #0: ffff88813fe0f548 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3250 [inline]
 #0: ffff88813fe0f548 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9ea/0x1830 kernel/workqueue.c:3358
 #1: ffffc900001e7c40 ((work_completion)(&data->fib_event_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3251 [inline]
 #1: ffffc900001e7c40 ((work_completion)(&data->fib_event_work)){+.+.}-{0:0}, at: process_scheduled_works+0xa25/0x1830 kernel/workqueue.c:3358
 #2: ffff88807c222240 (&data->fib_lock){+.+.}-{4:4}, at: nsim_fib_event_work+0x202/0x3d0 drivers/net/netdevsim/fib.c:1490
1 lock held by khungtaskd/30:
 #0: ffffffff8e7602e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:312 [inline]
 #0: ffffffff8e7602e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:850 [inline]
 #0: ffffffff8e7602e0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
8 locks held by kworker/u8:2/35:
3 locks held by kworker/1:1/42:
3 locks held by kworker/u8:3/49:
 #0: ffff88813fe4c148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3250 [inline]
 #0: ffff88813fe4c148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x9ea/0x1830 kernel/workqueue.c:3358
 #1: ffffc90000b97c40 ((work_completion)(&pool->idle_cull_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3251 [inline]
 #1: ffffc90000b97c40 ((work_completion)(&pool->idle_cull_work)){+.+.}-{0:0}, at: process_scheduled_works+0xa25/0x1830 kernel/workqueue.c:3358
 #2: ffffffff8e5fec68 (wq_pool_attach_mutex){+.+.}-{4:4}, at: idle_cull_fn+0xd2/0x740 kernel/workqueue.c:2973
2 locks held by kworker/u8:4/77:
3 locks held by kworker/u8:5/86:
 #0: ffff88813fe4c148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3250 [inline]
 #0: ffff88813fe4c148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x9ea/0x1830 kernel/workqueue.c:3358
 #1: ffffc900025dfc40 ((linkwatch_work).work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3251 [inline]
 #1: ffffc900025dfc40 ((linkwatch_work).work){+.+.}-{0:0}, at: process_scheduled_works+0xa25/0x1830 kernel/workqueue.c:3358
 #2: ffffffff8fbcb888 (rtnl_mutex){+.+.}-{4:4}, at: linkwatch_event+0xe/0x60 net/core/link_watch.c:313
2 locks held by kworker/u8:6/146:
2 locks held by kworker/0:2/796:
2 locks held by kworker/u8:7/1116:
1 lock held by kworker/u8:8/1147:
 #0: ffffffff8e5fec68 (wq_pool_attach_mutex){+.+.}-{4:4}, at: worker_attach_to_pool+0x2e/0x3a0 kernel/workqueue.c:2691
2 locks held by kworker/u8:9/1168:
1 lock held by kworker/1:2/1997:
 #0: ffffffff8e5fec68 (wq_pool_attach_mutex){+.+.}-{4:4}, at: worker_attach_to_pool+0x2e/0x3a0 kernel/workqueue.c:2691
3 locks held by kworker/u8:10/2990:
2 locks held by getty/5581:
 #0: ffff888036c110a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc9000332b2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x45c/0x13c0 drivers/tty/n_tty.c:2211
3 locks held by kworker/1:3/5810:
2 locks held by syz-executor210/5855:
 #0: ffffffff8fbcb888 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #0: ffffffff8fbcb888 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_nets_lock net/core/rtnetlink.c:341 [inline]
 #0: ffffffff8fbcb888 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_newlink+0x8a1/0x1be0 net/core/rtnetlink.c:4071
 #1: ffff88806d1a5528 (&wg->device_update_lock){+.+.}-{4:4}, at: wg_open+0x227/0x420 drivers/net/wireguard/device.c:50
1 lock held by syz-executor210/5856:
 #0: ffffffff8fbcb888 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline]
 #0: ffffffff8fbcb888 (rtnl_mutex){+.+.}-{4:4}, at: rtnetlink_rcv_msg+0x722/0xbe0 net/core/rtnetlink.c:6964
3 locks held by kworker/1:4/5865:
7 locks held by kworker/u9:3/5869:
 #0: ffff88807a26f948 ((wq_completion)hci2){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3250 [inline]
 #0: ffff88807a26f948 ((wq_completion)hci2){+.+.}-{0:0}, at: process_scheduled_works+0x9ea/0x1830 kernel/workqueue.c:3358
 #1: ffffc90003ba7c40 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3251 [inline]
 #1: ffffc90003ba7c40 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_scheduled_works+0xa25/0x1830 kernel/workqueue.c:3358
 #2: ffff888076408ec0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_cmd_sync_work+0x1d3/0x400 net/bluetooth/hci_sync.c:331
 #3: ffff8880764080c0 (&hdev->lock){+.+.}-{4:4}, at: hci_abort_conn_sync+0xa6f/0x1190 net/bluetooth/hci_sync.c:5734
 #4: ffffffff8fd57f28 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_connect_cfm include/net/bluetooth/hci_core.h:2136 [inline]
 #4: ffffffff8fd57f28 (hci_cb_list_lock){+.+.}-{4:4}, at: hci_conn_failed+0x165/0x340 net/bluetooth/hci_conn.c:1342
 #5: ffff888057b3caf8 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x7b/0x5c0 net/bluetooth/l2cap_core.c:1755
 #6: ffffffff8e766578 (rcu_state.exp_mutex){+.+.}-{4:4}, at: exp_funnel_lock kernel/rcu/tree_exp.h:343 [inline]
 #6: ffffffff8e766578 (rcu_state.exp_mutex){+.+.}-{4:4}, at: synchronize_rcu_expedited+0x38d/0x770 kernel/rcu/tree_exp.h:961
5 locks held by kworker/u9:4/5870:
 #0: ffff88807c3fa148 ((wq_completion)hci4){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3250 [inline]
 #0: ffff88807c3fa148 ((wq_completion)hci4){+.+.}-{0:0}, at: process_scheduled_works+0x9ea/0x1830 kernel/workqueue.c:3358

Crashes (25):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/25 18:27 net 2f61f38a2174 df2e85d4 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci-upstream-net-this-kasan-gce INFO: task hung in ret_from_fork
2026/01/23 23:59 upstream c072629f05d7 3181850c .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/12/28 18:32 upstream d26143bb38e2 d1b870e1 .config console log report info [disk image] [vmlinux] [kernel image] ci-qemu-gce-upstream-auto INFO: task hung in ret_from_fork
2025/12/20 19:09 upstream d8ba32c5a460 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/12/11 18:11 upstream d358e5254674 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/09/30 15:12 upstream 30d4efb2f5a5 65a0eece .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/07/22 16:47 upstream 89be9a83ccf1 85deaf45 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/06/26 11:02 upstream ee88bddf7f2f 26d77996 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/06/01 14:58 upstream 7d4e49a77d99 3d2f584d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/05/27 10:12 upstream 914873bc7df9 874a1386 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/03/12 07:45 upstream 0fed89a961ea ee70e6db .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/03/10 05:09 upstream 80e54e84911a 163f510d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/03/07 21:03 upstream 00a7d39898c8 7e3bd60d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2025/02/22 04:07 upstream ff202c5028a1 d34966d1 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2024/12/31 00:03 upstream ccb98ccef0e5 d3ccff63 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2024/10/27 15:45 upstream 850925a8133c 65e8686b .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2024/10/01 08:19 upstream e32cde8d2bd7 bbd4e0a4 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root INFO: task hung in ret_from_fork
2024/09/30 11:44 upstream 9852d85ec9d4 ba29ff75 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root INFO: task hung in ret_from_fork
2024/09/27 14:47 upstream 075dbe9f6e3c 2b1784d6 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2024/07/12 22:17 upstream e091caf99f3a eaeb5c15 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root INFO: task hung in ret_from_fork
2024/05/27 22:02 upstream 2bfcfd584ff5 f550015e .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in ret_from_fork
2024/11/12 06:00 upstream 2d5404caa8c7 75bb1b32 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 INFO: task hung in ret_from_fork
2024/10/05 16:46 upstream 27cc6fdf7201 d7906eff .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 INFO: task hung in ret_from_fork
2024/06/07 03:06 linux-next ee78a17615ad 121701b6 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root INFO: task hung in ret_from_fork
2025/03/15 13:06 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci a5618886fdab e2826670 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 INFO: task hung in ret_from_fork
* Struck through repros no longer work on HEAD.