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Sat, 08 Aug 2026 06:02:44 -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 2/2] samples: enhance hung_task detector test with rtmutex support Date: Sat, 8 Aug 2026 21:02:18 +0800 Message-Id: <4991cd8e1bbddb42a1fe31dde38f85d74ff1c4cc.1786193045.git.ruipengqi3@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Ruipeng Qi Extend the hung_task detector test module with an rtmutex test. When CONFIG_RT_MUTEXES is enabled, the module creates an additional "rtmutex" debugfs file under /hung_task. Concurrent reads hold and contend on an rtmutex for 256 seconds, allowing hung-task and blocker reporting to be tested for rtmutex waits. Usage is: > cd /sys/kernel/debug/hung_task > cat rtmutex & cat rtmutex Update the module usage comments and Kconfig description to document the rtmutex debugfs file. Signed-off-by: Ruipeng Qi --- samples/Kconfig | 2 +- samples/hung_task/hung_task_tests.c | 50 ++++++++++++++++++++++++++--- 2 files changed, 47 insertions(+), 5 deletions(-) diff --git a/samples/Kconfig b/samples/Kconfig index a75e8e78330da5..11096dbc43413f 100644 --- a/samples/Kconfig +++ b/samples/Kconfig @@ -318,7 +318,7 @@ config SAMPLE_HUNG_TASK depends on DETECT_HUNG_TASK && DEBUG_FS help Build a module that provides debugfs files (e.g., mutex, semaphore, - rw_semaphore_read, rw_semaphore_write) under /hung_task. + rw_semaphore_read, rw_semaphore_write, rtmutex) under /hung_task. Reading these files with multiple processes triggers hung task detection by holding locks for a long time (256 seconds). diff --git a/samples/hung_task/hung_task_tests.c b/samples/hung_task/hung_task_tests.c index 0360ec916890b3..87346d65f860a5 100644 --- a/samples/hung_task/hung_task_tests.c +++ b/samples/hung_task/hung_task_tests.c @@ -1,14 +1,16 @@ // SPDX-License-Identifier: GPL-2.0-or-later /* * hung_task_tests.c - Sample code for testing hung tasks with mutex, - * semaphore, etc. + * semaphore, rwsem, and rtmutex. * * Usage: Load this module and read `/hung_task/mutex`, * `/hung_task/semaphore`, `/hung_task/rw_semaphore_read`, - * `/hung_task/rw_semaphore_write`, etc., with 2 or more processes. + * `/hung_task/rw_semaphore_write`, and `/hung_task/rtmutex`, + * with 2 or more processes. * * This is for testing kernel hung_task error messages with various locking - * mechanisms (e.g., mutex, semaphore, rw_semaphore_read, rw_semaphore_write, etc.). + * mechanisms (e.g., mutex, semaphore, rw_semaphore_read, rw_semaphore_write, + * and rtmutex). * Note that this may freeze your system or cause a panic. Use only for testing purposes. */ @@ -17,6 +19,7 @@ #include #include #include +#include #include #include @@ -25,10 +28,16 @@ #define HUNG_TASK_SEM_FILE "semaphore" #define HUNG_TASK_RWSEM_READ_FILE "rw_semaphore_read" #define HUNG_TASK_RWSEM_WRITE_FILE "rw_semaphore_write" +#ifdef CONFIG_RT_MUTEXES +#define HUNG_TASK_RTMUTEX_FILE "rtmutex" +#endif #define SLEEP_SECOND 256 static const char dummy_string[] = "This is a dummy string."; static DEFINE_MUTEX(dummy_mutex); +#ifdef CONFIG_RT_MUTEXES +static DEFINE_RT_MUTEX(dummy_rtmutex); +#endif static DEFINE_SEMAPHORE(dummy_sem, 1); static DECLARE_RWSEM(dummy_rwsem); static struct dentry *hung_task_dir; @@ -51,6 +60,28 @@ static ssize_t read_dummy_mutex(struct file *file, char __user *user_buf, sizeof(dummy_string)); } +#ifdef CONFIG_RT_MUTEXES +/* RT mutex-based read function */ +static ssize_t read_dummy_rtmutex(struct file *file, char __user *user_buf, + size_t count, loff_t *ppos) +{ + /* Check if data is already read */ + if (*ppos >= sizeof(dummy_string)) + return 0; + + /* Second task waits on rtmutex, entering uninterruptible sleep */ + rt_mutex_lock(&dummy_rtmutex); + + /* First task sleeps here, interruptible */ + msleep_interruptible(SLEEP_SECOND * 1000); + + rt_mutex_unlock(&dummy_rtmutex); + + return simple_read_from_buffer(user_buf, count, ppos, dummy_string, + sizeof(dummy_string)); +} +#endif + /* Semaphore-based read function */ static ssize_t read_dummy_semaphore(struct file *file, char __user *user_buf, size_t count, loff_t *ppos) @@ -116,6 +147,13 @@ static const struct file_operations hung_task_mutex_fops = { .read = read_dummy_mutex, }; +#ifdef CONFIG_RT_MUTEXES +/* File operations for rtmutex */ +static const struct file_operations hung_task_rtmutex_fops = { + .read = read_dummy_rtmutex, +}; +#endif + /* File operations for semaphore */ static const struct file_operations hung_task_sem_fops = { .read = read_dummy_semaphore, @@ -137,9 +175,13 @@ static int __init hung_task_tests_init(void) if (IS_ERR(hung_task_dir)) return PTR_ERR(hung_task_dir); - /* Create debugfs files for mutex and semaphore tests */ + /* Create debugfs files for lock tests */ debugfs_create_file(HUNG_TASK_MUTEX_FILE, 0400, hung_task_dir, NULL, &hung_task_mutex_fops); +#ifdef CONFIG_RT_MUTEXES + debugfs_create_file(HUNG_TASK_RTMUTEX_FILE, 0400, hung_task_dir, NULL, + &hung_task_rtmutex_fops); +#endif debugfs_create_file(HUNG_TASK_SEM_FILE, 0400, hung_task_dir, NULL, &hung_task_sem_fops); debugfs_create_file(HUNG_TASK_RWSEM_READ_FILE, 0400, hung_task_dir, NULL, -- 2.25.1