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Sat, 08 Aug 2026 06:02:31 -0700 (PDT) Received: from lixiang-ThinkCentre-M755e-N000.company.local ([210.184.73.204]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2d14ccae6f8sm18584645ad.1.2026.08.08.06.02.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 08 Aug 2026 06:02:31 -0700 (PDT) From: ruipengqi To: akpm@linux-foundation.org, peterz@infradead.org, bigeasy@linutronix.de Cc: lance.yang@linux.dev, 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, ruipengqi3@gmail.com Subject: [PATCH v2 0/2] hung_task: show the blocker task if the task is hung on rtmutex Date: Sat, 8 Aug 2026 21:02:16 +0800 Message-Id: X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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