syzbot


INFO: task hung in _free_event

Status: upstream: reported on 2025/11/09 04:01
Reported-by: syzbot+196f888bfb53580e9f43@syzkaller.appspotmail.com
First crash: 6d01h, last: 3d19h
Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in _free_event perf 1 C 2 338d 361d 28/29 fixed on 2025/06/10 16:19
android-414 INFO: task hung in _free_event 1 8 2332d 2399d 0/1 auto-closed as invalid on 2019/10/26 01:49
linux-4.19 INFO: task hung in _free_event 1 1 2016d 2016d 0/1 auto-closed as invalid on 2020/09/05 20:32
linux-6.1 INFO: task hung in _free_event origin:lts-only 1 C inconclusive 604 17h39m 439d 0/3 upstream: reported C repro on 2024/09/01 12:31
linux-4.14 INFO: task hung in _free_event 1 1 1889d 1889d 0/1 auto-closed as invalid on 2021/01/10 07:54
linux-6.6 INFO: task hung in _free_event origin:lts-only 1 C inconclusive 152 12h36m 151d 0/2 upstream: reported C repro on 2025/06/16 19:30

Sample crash report:
INFO: task syz.3.655:6762 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.3.655       state:D stack:26368 pid: 6762 ppid:  4186 flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11bb/0x4390 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_preempt_disabled+0xf/0x20 kernel/sched/core.c:6537
 __mutex_lock_common+0xc71/0x2390 kernel/locking/mutex.c:669
 __mutex_lock kernel/locking/mutex.c:729 [inline]
 mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743
 perf_trace_destroy+0x2a/0x140 kernel/trace/trace_event_perf.c:239
 _free_event+0x850/0xe60 kernel/events/core.c:5164
 put_event kernel/events/core.c:5258 [inline]
 perf_event_release_kernel+0x832/0x8c0 kernel/events/core.c:5383
 perf_release+0x37/0x40 kernel/events/core.c:5393
 __fput+0x234/0x930 fs/file_table.c:311
 task_work_run+0x125/0x1a0 kernel/task_work.c:188
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:181
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fa5cd4b76c9
RSP: 002b:00007ffc260a3a98 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007fa5cd70fda0 RCX: 00007fa5cd4b76c9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007fa5cd70fda0 R08: 00000000000001ec R09: 0000001b260a3d8f
R10: 00007fa5cd70fcb0 R11: 0000000000000246 R12: 0000000000024804
R13: 00007fa5cd70e090 R14: ffffffffffffffff R15: 00007ffc260a3bb0
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/27:
 #0: ffffffff8c11c760 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30
2 locks held by udevd/3561:
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
 #1: ffff88807da7a428 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #1: ffff88807da7a428 (&mm->mmap_lock){++++}-{3:3}, at: dup_mmap kernel/fork.c:504 [inline]
 #1: ffff88807da7a428 (&mm->mmap_lock){++++}-{3:3}, at: dup_mm kernel/fork.c:1466 [inline]
 #1: ffff88807da7a428 (&mm->mmap_lock){++++}-{3:3}, at: copy_mm+0x238/0x1380 kernel/fork.c:1518
1 lock held by dhcpcd/3854:
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
2 locks held by getty/3951:
 #0: ffff88802bf66098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:252
 #1: ffffc90002cf62e8 (&ldata->atomic_read_lock){+.+.}-{3:3}, at: n_tty_read+0x5ba/0x1a30 drivers/tty/n_tty.c:2158
1 lock held by udevd/5591:
 #0: ffff88807b43c028 (&mm->mmap_lock){++++}-{3:3}, at: mmap_write_lock_killable include/linux/mmap_lock.h:87 [inline]
 #0: ffff88807b43c028 (&mm->mmap_lock){++++}-{3:3}, at: __vm_munmap+0xf3/0x230 mm/mmap.c:2949
1 lock held by syz.3.655/6762:
 #0: ffffffff8c169e68 (event_mutex){+.+.}-{3:3}, at: perf_trace_destroy+0x2a/0x140 kernel/trace/trace_event_perf.c:239
4 locks held by syz.3.655/6763:
 #0: ffffffff96115918 (&pmus_srcu){....}-{0:0}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #1: ffffffff8c169e68 (event_mutex){+.+.}-{3:3}, at: perf_uprobe_init+0x11f/0x190 kernel/trace/trace_event_perf.c:335
 #2: ffff888061773090 (&uprobe->register_rwsem){+.+.}-{3:3}, at: uprobe_apply+0x3d/0xe0 kernel/events/uprobes.c:1226
 #3: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: register_for_each_vma+0x2f/0xbb0 kernel/events/uprobes.c:1041
1 lock held by syz-executor/6766:
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
1 lock held by syz-executor/6767:
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
1 lock held by syz-executor/6768:
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
1 lock held by syz-executor/6769:
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
1 lock held by syz-executor/6783:
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518
1 lock held by syz-executor/6794:
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mmap kernel/fork.c:503 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: dup_mm kernel/fork.c:1466 [inline]
 #0: ffffffff8c1a68f0 (dup_mmap_sem){++++}-{0:0}, at: copy_mm+0x21f/0x1380 kernel/fork.c:1518

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

NMI backtrace for cpu 0
CPU: 0 PID: 27 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x397/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:148 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:212 [inline]
 watchdog+0xe0f/0xe50 kernel/hung_task.c:369
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 4540 Comm: kworker/u4:6 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue:  0x0 (bat_events)
RIP: 0010:vtime_account_idle kernel/sched/cputime.c:-1 [inline]
RIP: 0010:vtime_task_switch_generic+0x184/0x570 kernel/sched/cputime.c:776
Code: 00 00 74 08 4c 89 e7 e8 4a 3f 68 00 49 01 1c 24 4c 29 f3 48 89 df e8 3b cf ff ff 49 bc 00 00 00 00 00 fc ff df 48 8b 5c 24 08 <4c> 8b 74 24 18 48 8b 6c 24 10 eb 0b 4c 89 ff 4c 89 f6 e8 d5 ee ff
RSP: 0018:ffffc9000325fb00 EFLAGS: 00000016
RAX: 1ffff11017224ee3 RBX: ffffffff81522976 RCX: ffffffff8153c4c5
RDX: 0000000000000000 RSI: 0000000000000004 RDI: ffff8880b913add8
RBP: 1ffff11027fc90ea R08: dffffc0000000000 R09: ffffed10172275bc
R10: ffffed10172275bc R11: 1ffff110172275bb R12: dffffc0000000000
R13: 1ffff11027fc90eb R14: 0000000000005312 R15: ffff88813fe48000
FS:  0000000000000000(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f1ca8735bf4 CR3: 000000007dd42000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000200000000300 DR6: 00000000ffff0ff8 DR7: 0000000000000600
Call Trace:
 <TASK>
 vtime_task_switch include/linux/vtime.h:95 [inline]
 finish_task_switch+0x3c6/0x640 kernel/sched/core.c:4917
 context_switch kernel/sched/core.c:5052 [inline]
 __schedule+0x11c3/0x4390 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 worker_thread+0xf5c/0x12a0 kernel/workqueue.c:2478
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/11 10:11 linux-5.15.y cc5ec8769306 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in _free_event
2025/11/09 04:01 linux-5.15.y cc5ec8769306 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: task hung in _free_event
* Struck through repros no longer work on HEAD.