From: Lance Yang <lance.yang@linux.dev>
To: ruipengqi <ruipengqi3@gmail.com>, peterz@infradead.org
Cc: mhiramat@kernel.org, pmladek@suse.com, mingo@redhat.com,
will@kernel.org, boqun@kernel.org, longman@redhat.com,
clrkwllms@kernel.org, rostedt@goodmis.org, zhouyuhang@kylinos.cn,
arnd@arndb.de, colin.i.king@gmail.com, ebiggers@kernel.org,
inux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev,
akpm@linux-foundation.org, bigeasy@linutronix.de
Subject: Re: [PATCH 0/2] hung_task: extend blocking task stacktrace dump to rtmutex
Date: Thu, 30 Jul 2026 13:06:08 +0800 [thread overview]
Message-ID: <138ba5ec-41a1-4fe3-851a-51dbb866afae@linux.dev> (raw)
In-Reply-To: <cover.1785376929.git.ruipengqi3@gmail.com>
Afraid Peter may still strongly object to this whole approach:
https://lore.kernel.org/lkml/20260325150336.GF3738786@noisy.programming.kicks-ass.net/
Emm ... did you reach out to Peter privately, hash this out off-list,
and get his okay to extend it to rtmutex?
Cheers, Lance
On 2026/7/30 10:29, 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
> implementations locks 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.
>
> On 64-bit systems, lock pointers are 8-byte aligned, so their three
> least significant bits are always zero. Use these bits to encode the
> blocker type.
>
> Unlike semaphores, rtmutex has built-in owner tracking via lock->owner,
> so no additional bookkeeping is needed. The owner can be read with
> rt_mutex_owner().
>
> 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>
>
> 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/hung_task.h | 31 +++++++++++++-----
> kernel/hung_task.c | 22 +++++++++++++
> kernel/locking/mutex.c | 4 +--
> kernel/locking/rtmutex.c | 13 ++++++++
> kernel/locking/rwsem.c | 8 ++---
> kernel/locking/semaphore.c | 4 +--
> lib/Kconfig.debug | 1 -
> samples/Kconfig | 2 +-
> samples/hung_task/hung_task_tests.c | 50 ++++++++++++++++++++++++++---
> 9 files changed, 113 insertions(+), 22 deletions(-)
>
prev parent reply other threads:[~2026-07-30 5:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-30 2:29 [PATCH 0/2] hung_task: extend blocking task stacktrace dump to rtmutex ruipengqi
2026-07-30 2:29 ` [PATCH 1/2] hung_task: show the blocker task if the task is hung on rtmutex ruipengqi
2026-07-30 2:50 ` Zhan Xusheng
2026-07-30 2:29 ` [PATCH 2/2] samples: enhance hung_task detector test with rtmutex support ruipengqi
2026-07-30 5:06 ` Lance Yang [this message]
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