Re: [PATCH v2 0/2] hung_task: show the blocker task if the task is hung on rtmutex

[Ruipeng Qi <ruipengqi3@gmail.com>]

On 8/8/2026 11:34 PM, Lance Yang wrote:
> Hi Ruipeng,
>
> Guess I'll have to be the bad guy here ...
>
> Already raised this in v1 [1], but never got an answer ...
>
> This touches locking too, and Peter has already made it pretty clear he
> doesn't want this kind of debug code there.

Hi, Lance

Peter remains opposed to this kind of debug code, so I will cease work 
on this patch series. Thank you.


Best Regards，
Ruipeng

> Please don't send another version unless Peter is on board. Otherwise,
> just spinning wheels ...
>
> [1]https://lore.kernel.org/all/138ba5ec-41a1-4fe3-851a-51dbb866afae@linux.dev/
>
> Thanks, Lance
>
> On Sat, Aug 08, 2026 at 09:02:16PM +0800, ruipengqi wrote:
>> From: Ruipeng Qi<ruipengqi3@gmail.com>
>>
>> Currently, debug_show_blocker() only tracks mutex, semaphore and rwsem
>> lock types. Extend it to also cover rtmutex or rt_mutex-based lock
>> implementations on PREEMPT_RT, so that when a task is hung on an
>> rtmutex, the hung task detector can identify and report which task holds
>> the lock.
>>
>> Add rt_mutex_task_owner() to get the task's lock owner when a task is
>> blocked by an rtmutex-based lock implementation.
>>
>> Since the LSBs of task->blocker pointer are already fully utilized and
>> leave no room for new blocker types, this version avoids adding a new
>> blocker type by directly leveraging rt_mutex_task_owner() to retrieve
>> the lock owner information.
>>
>> With this change, the hung task detector can now show blocker task's
>> info like below:
>>
>> [ 3000.899985] INFO: task cat:195 blocked for more than 120 seconds.
>> [ 3000.900561]       Not tainted 7.2.0-rc4-00366-gf339a6eb59f3-dirty #22
>> [ 3000.900930] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
>> [ 3000.901376] task:cat             state:D stack:13784 pid:195   tgid:195   ppid:1      task_flags:0x400000 flags:0x00080000
>> [ 3000.902081] Call Trace:
>> [ 3000.902233]  <TASK>
>> [ 3000.902383]  __schedule+0x514/0xf50
>> [ 3000.902677]  rt_mutex_schedule+0x1b/0x30
>> [ 3000.902916]  rt_mutex_slowlock_block.constprop.0+0x3b/0x1c0
>> [ 3000.903242]  __rt_mutex_slowlock_locked.constprop.0+0xa8/0x200
>> [ 3000.903716]  rt_mutex_slowlock.constprop.0+0x48/0xb0
>> [ 3000.904023]  rt_mutex_lock+0x32/0x40
>> [ 3000.904249]  read_dummy_rtmutex+0x2a/0x60 [hung_task_tests]
>> [ 3000.904647]  full_proxy_read+0x5b/0x90
>> [ 3000.904843]  vfs_read+0xb0/0x370
>> [ 3000.905051]  ? vm_mmap_pgoff+0xf1/0x1b0
>> [ 3000.905293]  ? vm_mmap_pgoff+0x122/0x1b0
>> [ 3000.905684]  ksys_read+0x68/0xe0
>> [ 3000.905980]  do_syscall_64+0xf9/0x540
>> [ 3000.906213]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>> [ 3000.906643] RIP: 0033:0x49a182
>> [ 3000.906844] RSP: 002b:00007ffc431f6528 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
>> [ 3000.907251] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000049a182
>> [ 3000.907673] RDX: 0000000000010000 RSI: 00007f69b2166000 RDI: 0000000000000003
>> [ 3000.908044] RBP: 00007f69b2166000 R08: 00000000ffffffff R09: 0000000000000000
>> [ 3000.908485] R10: 0000000000000022 R11: 0000000000000246 R12: 0000000000010000
>> [ 3000.908816] R13: 0000000000000003 R14: 0000000000000001 R15: 0000000001000000
>> [ 3000.909206]  </TASK>
>> [ 3000.909351] INFO: task cat:195 is blocked on a rtmutex likely owned by task cat:194.
>> [ 3000.909832] task:cat             state:S stack:13784 pid:194   tgid:194   ppid:1      task_flags:0x400000 flags:0x00080000
>> [ 3000.910426] Call Trace:
>> [ 3000.910618]  <TASK>
>> [ 3000.910727]  __schedule+0x514/0xf50
>> [ 3000.910912]  schedule+0x22/0xa0
>> [ 3000.911064]  schedule_timeout+0x81/0x100
>> [ 3000.911254]  ? __pfx_process_timeout+0x10/0x10
>> [ 3000.911522]  msleep_interruptible+0x28/0x50
>> [ 3000.911754]  read_dummy_rtmutex+0x34/0x60 [hung_task_tests]
>> [ 3000.912019]  full_proxy_read+0x5b/0x90
>> [ 3000.912212]  vfs_read+0xb0/0x370
>> [ 3000.912378]  ? vm_mmap_pgoff+0xf1/0x1b0
>> [ 3000.912630]  ? vm_mmap_pgoff+0x122/0x1b0
>> [ 3000.912839]  ksys_read+0x68/0xe0
>> [ 3000.913007]  do_syscall_64+0xf9/0x540
>> [ 3000.913187]  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>> [ 3000.913461] RIP: 0033:0x49a182
>> [ 3000.913618] RSP: 002b:00007ffd0b4cf048 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
>> [ 3000.913972] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000049a182
>> [ 3000.914294] RDX: 0000000000010000 RSI: 00007fbf49a0d000 RDI: 0000000000000003
>> [ 3000.914648] RBP: 00007fbf49a0d000 R08: 00000000ffffffff R09: 0000000000000000
>> [ 3000.914955] R10: 0000000000000022 R11: 0000000000000246 R12: 0000000000010000
>> [ 3000.915208] R13: 0000000000000003 R14: 0000000000000001 R15: 0000000001000000
>> [ 3000.915439]  </TASK>
>>
>> ---
>> v2 changes:
>> - Reduce #ifdef-ery by using rt_mutex_task_owner() instead of adding a new blocker type,
>> suggested by Petr.
>> - Remove the unused function debug_trace_blocker(), suggested by Xusheng.
>> - Clean up and update relevant comments.
>> -https://lore.kernel.org/all/cover.1785376929.git.ruipengqi3@gmail.com/
>>
>> Ruipeng Qi (2):
>>   hung_task: show the blocker task if the task is hung on rtmutex
>>   samples: enhance hung_task detector test with rtmutex support
>>
>> include/linux/rtmutex.h             |  2 ++
>> kernel/hung_task.c                  | 26 +++++++++++++--
>> kernel/locking/rtmutex_api.c        | 29 +++++++++++++++++
>> lib/Kconfig.debug                   |  1 -
>> samples/Kconfig                     |  2 +-
>> samples/hung_task/hung_task_tests.c | 50 ++++++++++++++++++++++++++---
>> 6 files changed, 101 insertions(+), 9 deletions(-)
>>
>> -- 
>> 2.25.1
>>
>>