INFO: task hung in synchronize_rcu

Status: upstream: reported on 2025/10/30 17:16
Reported-by: syzbot+6d7cbd2cd15cb48338f3@syzkaller.appspotmail.com
First crash: 269d, last: 23h22m
Similar bugs (16)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in synchronize_rcu (3) 1 C done done 374 1258d 2195d 22/29 fixed on 2023/02/24 13:50
linux-6.1 INFO: task hung in synchronize_rcu origin:lts-only 1 C unreliable 56 19d 1213d 0/3 upstream: reported C repro on 2023/04/01 04:49
android-6-12 INFO: task hung in synchronize_rcu (3) 1 2 4d17h 16d 0/1 premoderation: reported on 2026/07/10 14:29
android-49 INFO: task hung in synchronize_rcu 1 1 2431d 2431d 0/3 auto-closed as invalid on 2020/03/28 16:57
linux-4.14 INFO: task hung in synchronize_rcu vfs 1 C error 162 1272d 2454d 0/1 upstream: reported C repro on 2019/11/07 04:32
linux-4.19 INFO: task hung in synchronize_rcu 1 C error 70 1261d 2452d 0/1 upstream: reported C repro on 2019/11/08 21:27
linux-5.15 INFO: task hung in synchronize_rcu 1 1 1198d 1198d 0/3 auto-obsoleted due to no activity on 2023/08/14 02:05
android-6-12 INFO: task hung in synchronize_rcu 1 41 256d 380d 0/1 auto-obsoleted due to no activity on 2026/01/01 15:51
linux-5.15 INFO: task hung in synchronize_rcu (3) origin:lts-only 1 C error 56 3d00h 731d 0/3 upstream: reported C repro on 2024/07/26 03:55
upstream INFO: task hung in synchronize_rcu 1 syz done 1206 2431d 2458d 14/29 fixed on 2019/11/29 15:48
upstream INFO: task hung in synchronize_rcu (4) prio:high fs net 1 C done error 4152 3h26m 1180d 0/29 upstream: reported C repro on 2023/05/04 02:01
linux-5.15 INFO: task hung in synchronize_rcu (2) 1 1 886d 886d 0/3 auto-obsoleted due to no activity on 2024/05/31 13:53
android-414 INFO: task hung in synchronize_rcu 1 1 2449d 2449d 0/1 auto-closed as invalid on 2020/03/10 10:42
upstream INFO: task hung in synchronize_rcu (2) trace 1 8 2430d 2431d 0/29 closed as invalid on 2019/11/30 16:54
android-6-12 INFO: task hung in synchronize_rcu (2) 1 5 121d 162d 0/1 auto-obsoleted due to no activity on 2026/06/25 10:28
upstream INFO: task hung in rtnetlink_rcv_msg net 1 C inconclusive inconclusive 1970 748d 2711d 26/29 fixed on 2024/07/09 19:14

Sample crash report:
INFO: task kworker/u4:0:11 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u4:0    state:D stack:22376 pid:11    ppid:2      flags:0x00004000
Workqueue: events_unbound fsnotify_mark_destroy_workfn
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5382 [inline]
 __schedule+0x15ae/0x4660 kernel/sched/core.c:6701
 schedule+0xbd/0x170 kernel/sched/core.c:6775
 schedule_timeout+0xc1/0x2d0 kernel/time/timer.c:2144
 do_wait_for_common kernel/sched/completion.c:95 [inline]
 __wait_for_common kernel/sched/completion.c:116 [inline]
 wait_for_common kernel/sched/completion.c:127 [inline]
 wait_for_completion+0x2c6/0x5a0 kernel/sched/completion.c:148
 __synchronize_srcu+0x339/0x3d0 kernel/rcu/srcutree.c:1386
 fsnotify_mark_destroy_workfn+0x10a/0x2e0 fs/notify/mark.c:928
 process_one_work kernel/workqueue.c:2653 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2730
 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2811
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
INFO: task kworker/u4:2:42 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u4:2    state:D stack:21512 pid:42    ppid:2      flags:0x00004000
Workqueue: netns cleanup_net
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5382 [inline]
 __schedule+0x15ae/0x4660 kernel/sched/core.c:6701
 schedule+0xbd/0x170 kernel/sched/core.c:6775
 schedule_timeout+0xc1/0x2d0 kernel/time/timer.c:2144
 do_wait_for_common kernel/sched/completion.c:95 [inline]
 __wait_for_common kernel/sched/completion.c:116 [inline]
 wait_for_common kernel/sched/completion.c:127 [inline]
 wait_for_completion+0x2c6/0x5a0 kernel/sched/completion.c:148
 __flush_workqueue+0x666/0x1380 kernel/workqueue.c:3260
 peer_remove_after_dead+0x94/0x1a0 drivers/net/wireguard/peer.c:116
 wg_peer_remove_all+0x44d/0x4f0 drivers/net/wireguard/peer.c:183
 wg_destruct+0x17a/0x310 drivers/net/wireguard/device.c:255
 netdev_run_todo+0xbe7/0xdb0 net/core/dev.c:10631
 default_device_exit_batch+0x967/0xa00 net/core/dev.c:11747
 ops_exit_list net/core/net_namespace.c:178 [inline]
 cleanup_net+0x792/0xbb0 net/core/net_namespace.c:652
 process_one_work kernel/workqueue.c:2653 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2730
 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2811
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
INFO: task kworker/u4:11:3487 blocked for more than 144 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u4:11   state:D stack:22632 pid:3487  ppid:2      flags:0x00004000
Workqueue: events_unbound fsnotify_connector_destroy_workfn
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5382 [inline]
 __schedule+0x15ae/0x4660 kernel/sched/core.c:6701
 schedule+0xbd/0x170 kernel/sched/core.c:6775
 schedule_timeout+0xc1/0x2d0 kernel/time/timer.c:2144
 do_wait_for_common kernel/sched/completion.c:95 [inline]
 __wait_for_common kernel/sched/completion.c:116 [inline]
 wait_for_common kernel/sched/completion.c:127 [inline]
 wait_for_completion+0x2c6/0x5a0 kernel/sched/completion.c:148
 __synchronize_srcu+0x339/0x3d0 kernel/rcu/srcutree.c:1386
 fsnotify_connector_destroy_workfn+0x44/0xa0 fs/notify/mark.c:234
 process_one_work kernel/workqueue.c:2653 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2730
 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2811
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>

Showing all locks held in the system:
2 locks held by kworker/u4:0/11:
 #0: ffff888017c71538 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
 #0: ffff888017c71538 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
 #1: ffffc90000107d00 ((reaper_work).work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
 #1: ffffc90000107d00 ((reaper_work).work){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
1 lock held by khungtaskd/29:
 #0: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 #0: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: rcu_read_lock include/linux/rcupdate.h:786 [inline]
 #0: ffffffff8d131da0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x55/0x290 kernel/locking/lockdep.c:6633
4 locks held by kworker/u4:2/42:
 #0: ffff88801a25c938 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
 #0: ffff88801a25c938 ((wq_completion)netns){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
 #1: ffffc90000b2fd00 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
 #1: ffffc90000b2fd00 (net_cleanup_work){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
 #2: ffffffff8e3c9b10 (pernet_ops_rwsem){++++}-{3:3}, at: cleanup_net+0x14c/0xbb0 net/core/net_namespace.c:606
 #3: ffff88805520d468 (&wg->device_update_lock){+.+.}-{3:3}, at: wg_destruct+0x116/0x310 drivers/net/wireguard/device.c:250
2 locks held by kworker/u4:11/3487:
 #0: ffff888017c71538 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
 #0: ffff888017c71538 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
 #1: ffffc9000cac7d00 (connector_reaper_work){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
 #1: ffffc9000cac7d00 (connector_reaper_work){+.+.}-{0:0}, at: process_scheduled_works+0x975/0x1600 kernel/workqueue.c:2730
1 lock held by udevd/5143:
 #0: ffffffff8d15bbd0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x21d0/0x3da0 kernel/fork.c:2605
2 locks held by getty/5537:
 #0: ffff88802cb0f0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc9000327b2f0 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x428/0x1370 drivers/tty/n_tty.c:2217
1 lock held by kworker/dying/23185:
 #0: ffffffff8d15bbd0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x601/0x2530 kernel/exit.c:831
1 lock held by syz-executor/30017:
 #0: ffffffff8d15bbd0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x601/0x2530 kernel/exit.c:831
6 locks held by syz-executor/30619:
1 lock held by syz.9.7866/30647:
1 lock held by udevd/30785:
 #0: ffffffff8d15bbd0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: do_exit+0x601/0x2530 kernel/exit.c:831
1 lock held by syz-executor/30787:
 #0: ffffffff8d15bbd0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x21d0/0x3da0 kernel/fork.c:2605
1 lock held by dhcpcd-run-hook/30789:
 #0: ffffffff8d15bbd0 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x21d0/0x3da0 kernel/fork.c:2605

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 29 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x3a6/0x3e0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x2f0 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:222 [inline]
 watchdog+0xf59/0xfa0 kernel/hung_task.c:379
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 30680 Comm: syz.2.7870 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:arch_static_branch arch/x86/include/asm/jump_label.h:27 [inline]
RIP: 0010:static_key_false include/linux/jump_label.h:207 [inline]
RIP: 0010:native_write_msr arch/x86/include/asm/msr.h:147 [inline]
RIP: 0010:wrmsr arch/x86/include/asm/msr.h:254 [inline]
RIP: 0010:native_apic_msr_write+0x39/0x50 arch/x86/include/asm/apic.h:196
Code: 74 2a 83 ff 30 74 25 eb 10 81 ff d0 00 00 00 74 1b 81 ff e0 00 00 00 74 13 c1 ef 04 81 c7 00 08 00 00 89 f9 89 f0 31 d2 0f 30 <66> 90 c3 89 f6 31 d2 e9 2b 7f 2b 03 66 2e 0f 1f 84 00 00 00 00 00
RSP: 0018:ffffc90000007e80 EFLAGS: 00000046
RAX: 000000000004213c RBX: ffff8880b8e282c0 RCX: 0000000000000838
RDX: 0000000000000000 RSI: 000000000004213c RDI: 0000000000000838
RBP: 0000000000000000 R08: ffffffff8e8c7caf R09: 1ffffffff1d18f95
R10: dffffc0000000000 R11: fffffbfff1d18f96 R12: dffffc0000000000
R13: 0000000010004b7f R14: 000000000004213c R15: 0000000000000020
FS:  00007f03f9ee06c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000000 CR3: 00000000696b2000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 apic_write arch/x86/include/asm/apic.h:404 [inline]
 lapic_next_event+0x11/0x20 arch/x86/kernel/apic/apic.c:448
 clockevents_program_event+0x1c0/0x310 kernel/time/clockevents.c:334
 hrtimer_interrupt+0x565/0x980 kernel/time/hrtimer.c:1893
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1077 [inline]
 __sysvec_apic_timer_interrupt+0xfb/0x3b0 arch/x86/kernel/apic/apic.c:1094
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0x9f/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:__get_user_nocheck_4+0x7/0x20 arch/x86/lib/getuser.S:124
Code: 90 90 90 f3 0f 1e fa 0f 01 cb 0f ae e8 0f b7 10 31 c0 0f 01 ca c3 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 01 cb <0f> ae e8 8b 10 31 c0 0f 01 ca c3 90 90 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc900034a78f8 EFLAGS: 00040202
RAX: 00007f03f9edfe40 RBX: 00007f03f9edfe10 RCX: 0000000000000000
RDX: ffffc9000cb99000 RSI: 0000000000000000 RDI: 0000000000080000
RBP: ffffc900034a7ad0 R08: ffffc900034a79cf R09: 1ffff92000694f39
R10: dffffc0000000000 R11: fffff52000694f3a R12: 0000000000000000
R13: 00007f03f9edfe40 R14: dffffc0000000000 R15: 0000000000000000
 save_xstate_epilog arch/x86/kernel/fpu/signal.c:139 [inline]
 copy_fpstate_to_sigframe+0xa99/0xce0 arch/x86/kernel/fpu/signal.c:245
 get_sigframe+0x5de/0x7d0 arch/x86/kernel/signal.c:142
 x64_setup_rt_frame+0x164/0xc30 arch/x86/kernel/signal_64.c:175
 setup_rt_frame arch/x86/kernel/signal.c:223 [inline]
 handle_signal arch/x86/kernel/signal.c:267 [inline]
 arch_do_signal_or_restart+0x411/0x7b0 arch/x86/kernel/signal.c:312
 exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
 do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f03f8f9de97
Code: 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 <0f> 05 48 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89
RSP: 002b:00007f03f9ee0028 EFLAGS: 00000246
RAX: 0000000000000048 RBX: 00007f03f9225fa0 RCX: 00007f03f8f9de99
RDX: 0000200000000280 RSI: 0000000000000026 RDI: 0000000000000003
RBP: 00007f03f9033eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f03f9226038 R14: 00007f03f9225fa0 R15: 00007fff23445248
 </TASK>

Crashes (9):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/26 10:55 linux-6.6.y c5596480c50e 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: task hung in synchronize_rcu
2026/06/28 15:03 linux-6.6.y d1cfde2d5d15 fb92f11c .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: task hung in synchronize_rcu
2026/06/25 17:40 linux-6.6.y d1cfde2d5d15 cfa969bf .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: task hung in synchronize_rcu
2026/04/26 13:45 linux-6.6.y 9760bf04666d 9c2d0995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: task hung in synchronize_rcu
2026/04/20 05:23 linux-6.6.y 9760bf04666d 303e2802 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: task hung in synchronize_rcu
2026/01/15 21:39 linux-6.6.y c596736dadab d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: task hung in synchronize_rcu
2025/12/22 06:24 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: task hung in synchronize_rcu
2025/12/10 21:00 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: task hung in synchronize_rcu
2025/10/30 17:16 linux-6.6.y e5bbb12db2c7 2c50b6a9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan INFO: task hung in synchronize_rcu
* Struck through repros no longer work on HEAD.