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Sun, 23 Aug 2026 19:02:25 -0700 (PDT) Message-ID: <7686ada4-0b67-4df5-82bb-b5dfdf050fc2@gmail.com> Date: Mon, 24 Aug 2026 10:02:25 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Ruipeng Qi Subject: Re: [PATCH v2 0/2] hung_task: show the blocker task if the task is hung on rtmutex To: Lance Yang Cc: akpm@linux-foundation.org, peterz@infradead.org, bigeasy@linutronix.de, mhiramat@kernel.org, pmladek@suse.com, mingo@redhat.com, will@kernel.org, boqun@kernel.org, longman@redhat.com, clrkwllms@kernel.org, rostedt@goodmis.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev References: <20260808153416.49698-1-lance.yang@linux.dev> Content-Language: en-US In-Reply-To: <20260808153416.49698-1-lance.yang@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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 >> >> 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] >> [ 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] >> [ 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] >> [ 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] >> >> --- >> 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 >> >>