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INFO: task hung in synchronize_rcu

Status: upstream: reported on 2025/10/30 17:16
Reported-by: syzbot+6d7cbd2cd15cb48338f3@syzkaller.appspotmail.com
First crash: 92d, last: 15d
▶ ▼ Similar bugs (14)
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 1080d 2018d 22/29 fixed on 2023/02/24 13:50
linux-6.1 INFO: task hung in synchronize_rcu origin:lts-only 1 C unreliable 26 27d 1035d 0/3 upstream: reported C repro on 2023/04/01 04:49
android-49 INFO: task hung in synchronize_rcu 1 1 2254d 2254d 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 1095d 2276d 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 1084d 2275d 0/1 upstream: reported C repro on 2019/11/08 21:27
linux-5.15 INFO: task hung in synchronize_rcu 1 1 1020d 1020d 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 79d 203d 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 15 38d 553d 0/3 upstream: reported C repro on 2024/07/26 03:55
upstream INFO: task hung in synchronize_rcu 1 syz done 1206 2254d 2280d 14/29 fixed on 2019/11/29 15:48
upstream INFO: task hung in synchronize_rcu (4) net fs 1 C done error 2488 1h42m 1002d 0/29 upstream: reported C repro on 2023/05/04 02:01
linux-5.15 INFO: task hung in synchronize_rcu (2) 1 1 709d 709d 0/3 auto-obsoleted due to no activity on 2024/05/31 13:53
android-414 INFO: task hung in synchronize_rcu 1 1 2272d 2272d 0/1 auto-closed as invalid on 2020/03/10 10:42
upstream INFO: task hung in synchronize_rcu (2) trace 1 8 2253d 2254d 0/29 closed as invalid on 2019/11/30 16:54
upstream INFO: task hung in rtnetlink_rcv_msg net 1 C inconclusive inconclusive 1970 570d 2534d 26/29 fixed on 2024/07/09 19:14

Sample crash report:
INFO: task kworker/u4:5:1096 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u4:5    state:D stack:24776 pid:1096  ppid:2      flags:0x00004000
Workqueue: events_unbound bpf_map_free_deferred
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 exp_funnel_lock kernel/rcu/tree_exp.h:315 [inline]
 synchronize_rcu_expedited+0x720/0x830 kernel/rcu/tree_exp.h:1004
 synchronize_rcu+0x136/0x380 kernel/rcu/tree.c:3627
 lockdep_unregister_key+0x4d0/0x580 kernel/locking/lockdep.c:6494
 htab_map_free+0x9a3/0xa50 kernel/bpf/hashtab.c:1586
 bpf_map_free_deferred+0xfc/0x120 kernel/bpf/syscall.c:703
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 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/u4:7:2912 blocked for more than 146 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u4:7    state:D stack:23080 pid:2912  ppid:2      flags:0x00004000
Workqueue: events_unbound linkwatch_event
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:6833
 __mutex_lock_common kernel/locking/mutex.c:679 [inline]
 __mutex_lock+0x6b7/0xcc0 kernel/locking/mutex.c:747
 linkwatch_event+0xe/0x60 net/core/link_watch.c:286
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 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/u4:8:2936 blocked for more than 147 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:kworker/u4:8    state:D stack:23592 pid:2936  ppid:2      flags:0x00004000
Workqueue: events_unbound bpf_map_free_deferred
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 exp_funnel_lock kernel/rcu/tree_exp.h:315 [inline]
 synchronize_rcu_expedited+0x720/0x830 kernel/rcu/tree_exp.h:1004
 synchronize_rcu+0x136/0x380 kernel/rcu/tree.c:3627
 lockdep_unregister_key+0x4d0/0x580 kernel/locking/lockdep.c:6494
 htab_map_free+0x9a3/0xa50 kernel/bpf/hashtab.c:1586
 bpf_map_free_deferred+0xfc/0x120 kernel/bpf/syscall.c:703
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 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 syz-executor:5957 blocked for more than 148 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor    state:D stack:21736 pid:5957  ppid:1      flags:0x00004006
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 exp_funnel_lock kernel/rcu/tree_exp.h:315 [inline]
 synchronize_rcu_expedited+0x720/0x830 kernel/rcu/tree_exp.h:1004
 namespace_unlock+0x1e7/0x3c0 fs/namespace.c:1581
 drop_collected_mounts fs/namespace.c:2083 [inline]
 put_mnt_ns+0xdf/0x130 fs/namespace.c:4802
 free_nsproxy+0x4d/0x3c0 kernel/nsproxy.c:193
 do_exit+0x906/0x23c0 kernel/exit.c:882
 do_group_exit+0x21b/0x2d0 kernel/exit.c:1024
 get_signal+0x12fc/0x1400 kernel/signal.c:2902
 arch_do_signal_or_restart+0x9c/0x7b0 arch/x86/kernel/signal.c:310
 exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0xf6/0x180 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: 0033:0x7fad99985897
RSP: 002b:00007ffdf7e7b8f0 EFLAGS: 00000293 ORIG_RAX: 000000000000003d
RAX: fffffffffffffe00 RBX: 000000000000005a RCX: 00007fad99985897
RDX: 0000000040000000 RSI: 00007ffdf7e7b95c RDI: 00000000ffffffff
RBP: 00007ffdf7e7b95c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000020
R13: 000055558256e590 R14: 0000000000028960 R15: 00007ffdf7e7b9b0
 </TASK>
INFO: task syz.4.188:6683 blocked for more than 150 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.4.188       state:D stack:28584 pid:6683  ppid:5952   flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:6833
 __mutex_lock_common kernel/locking/mutex.c:679 [inline]
 __mutex_lock+0x6b7/0xcc0 kernel/locking/mutex.c:747
 perf_trace_init+0x50/0x2d0 kernel/trace/trace_event_perf.c:221
 perf_tp_event_init+0x8d/0x110 kernel/events/core.c:10204
 perf_try_init_event+0x12b/0x3c0 kernel/events/core.c:11818
 perf_init_event kernel/events/core.c:11888 [inline]
 perf_event_alloc+0xfa4/0x21b0 kernel/events/core.c:12169
 __do_sys_perf_event_open kernel/events/core.c:12676 [inline]
 __se_sys_perf_event_open+0x70e/0x1c20 kernel/events/core.c:12567
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc77f38f749
RSP: 002b:00007fc7801e6038 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
RAX: ffffffffffffffda RBX: 00007fc77f5e5fa0 RCX: 00007fc77f38f749
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000500
RBP: 00007fc77f413f91 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc77f5e6038 R14: 00007fc77f5e5fa0 R15: 00007ffc1f799f78
 </TASK>
INFO: task syz.4.188:6685 blocked for more than 152 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.4.188       state:D stack:25832 pid:6685  ppid:5952   flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:6833
 __mutex_lock_common kernel/locking/mutex.c:679 [inline]
 __mutex_lock+0x6b7/0xcc0 kernel/locking/mutex.c:747
 perf_trace_init+0x50/0x2d0 kernel/trace/trace_event_perf.c:221
 perf_tp_event_init+0x8d/0x110 kernel/events/core.c:10204
 perf_try_init_event+0x12b/0x3c0 kernel/events/core.c:11818
 perf_init_event kernel/events/core.c:11888 [inline]
 perf_event_alloc+0xfa4/0x21b0 kernel/events/core.c:12169
 __do_sys_perf_event_open kernel/events/core.c:12676 [inline]
 __se_sys_perf_event_open+0x70e/0x1c20 kernel/events/core.c:12567

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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.