From: Zi Li <amaindex@outlook.com>
Extend the existing hung_task detector test module to support multiple lock
types, including mutex and semaphore, with room for future additions (e.g.,
spinlock, etc.). This module creates dummy files under <debugfs>/hung_task,
such as 'mutex' and 'semaphore'. The read process on any of these files will
sleep for enough long time (256 seconds) while holding the respective lock.
As a result, the second process will wait on the lock for a prolonged
duration and be detected by the hung_task detector.
This change unifies the previous mutex-only sample into a single,
extensible hung_task_tests module, reducing code duplication and improving
maintainability.
Usage is:
> cd /sys/kernel/debug/hung_task
> cat mutex & cat mutex # Test mutex blocking
> cat semaphore & cat semaphore # Test semaphore blocking
Update the Kconfig description to reflect multiple debugfs files support.
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Lance Yang <ioworker0@gmail.com>
Signed-off-by: Zi Li <amaindex@outlook.com>
---
samples/Kconfig | 9 +--
samples/hung_task/Makefile | 2 +-
samples/hung_task/hung_task_mutex.c | 66 --------------------
samples/hung_task/hung_task_tests.c | 97 +++++++++++++++++++++++++++++
4 files changed, 103 insertions(+), 71 deletions(-)
delete mode 100644 samples/hung_task/hung_task_mutex.c
create mode 100644 samples/hung_task/hung_task_tests.c
diff --git a/samples/Kconfig b/samples/Kconfig
index 09011be2391a..753ed1f170b5 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -304,10 +304,11 @@ config SAMPLE_HUNG_TASK
tristate "Hung task detector test code"
depends on DETECT_HUNG_TASK && DEBUG_FS
help
- Build a module which provide a simple debugfs file. If user reads
- the file, it will sleep long time (256 seconds) with holding a
- mutex. Thus if there are 2 or more processes read this file, it
- will be detected by the hung_task watchdog.
+ Build a module that provides debugfs files (e.g., mutex, semaphore,
+ etc.) under <debugfs>/hung_task. If user reads one of these files,
+ it will sleep long time (256 seconds) with holding a lock. Thus,
+ if 2 or more processes read the same file concurrently, it will
+ be detected by the hung_task watchdog.
source "samples/rust/Kconfig"
diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
index fe9dde799880..86036f1a204d 100644
--- a/samples/hung_task/Makefile
+++ b/samples/hung_task/Makefile
@@ -1,2 +1,2 @@
# SPDX-License-Identifier: GPL-2.0-only
-obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_mutex.o
\ No newline at end of file
+obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_tests.o
diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_task_mutex.c
deleted file mode 100644
index 7a29f2246d22..000000000000
--- a/samples/hung_task/hung_task_mutex.c
+++ /dev/null
@@ -1,66 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- * hung_task_mutex.c - Sample code which causes hung task by mutex
- *
- * Usage: load this module and read `<debugfs>/hung_task/mutex`
- * by 2 or more processes.
- *
- * This is for testing kernel hung_task error message.
- * Note that this will make your system freeze and maybe
- * cause panic. So do not use this except for the test.
- */
-
-#include <linux/debugfs.h>
-#include <linux/delay.h>
-#include <linux/fs.h>
-#include <linux/module.h>
-#include <linux/mutex.h>
-
-#define HUNG_TASK_DIR "hung_task"
-#define HUNG_TASK_FILE "mutex"
-#define SLEEP_SECOND 256
-
-static const char dummy_string[] = "This is a dummy string.";
-static DEFINE_MUTEX(dummy_mutex);
-struct dentry *hung_task_dir;
-
-static ssize_t read_dummy(struct file *file, char __user *user_buf,
- size_t count, loff_t *ppos)
-{
- /* If the second task waits on the lock, it is uninterruptible sleep. */
- guard(mutex)(&dummy_mutex);
-
- /* When the first task sleep here, it is interruptible. */
- msleep_interruptible(SLEEP_SECOND * 1000);
-
- return simple_read_from_buffer(user_buf, count, ppos,
- dummy_string, sizeof(dummy_string));
-}
-
-static const struct file_operations hung_task_fops = {
- .read = read_dummy,
-};
-
-static int __init hung_task_sample_init(void)
-{
- hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
- if (IS_ERR(hung_task_dir))
- return PTR_ERR(hung_task_dir);
-
- debugfs_create_file(HUNG_TASK_FILE, 0400, hung_task_dir,
- NULL, &hung_task_fops);
-
- return 0;
-}
-
-static void __exit hung_task_sample_exit(void)
-{
- debugfs_remove_recursive(hung_task_dir);
-}
-
-module_init(hung_task_sample_init);
-module_exit(hung_task_sample_exit);
-
-MODULE_LICENSE("GPL");
-MODULE_AUTHOR("Masami Hiramatsu");
-MODULE_DESCRIPTION("Simple sleep under mutex file for testing hung task");
diff --git a/samples/hung_task/hung_task_tests.c b/samples/hung_task/hung_task_tests.c
new file mode 100644
index 000000000000..a5c09bd3a47d
--- /dev/null
+++ b/samples/hung_task/hung_task_tests.c
@@ -0,0 +1,97 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * hung_task_tests.c - Sample code for testing hung tasks with mutex,
+ * semaphore, etc.
+ *
+ * Usage: Load this module and read `<debugfs>/hung_task/mutex`,
+ * `<debugfs>/hung_task/semaphore`, etc., with 2 or more processes.
+ *
+ * This is for testing kernel hung_task error messages with various locking
+ * mechanisms (e.g., mutex, semaphore, etc.). Note that this may freeze
+ * your system or cause a panic. Use only for testing purposes.
+ */
+
+#include <linux/debugfs.h>
+#include <linux/delay.h>
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/semaphore.h>
+
+#define HUNG_TASK_DIR "hung_task"
+#define HUNG_TASK_MUTEX_FILE "mutex"
+#define HUNG_TASK_SEM_FILE "semaphore"
+#define SLEEP_SECOND 256
+
+static const char dummy_string[] = "This is a dummy string.";
+static DEFINE_MUTEX(dummy_mutex);
+static DEFINE_SEMAPHORE(dummy_sem, 1);
+static struct dentry *hung_task_dir;
+
+/* Mutex-based read function */
+static ssize_t read_dummy_mutex(struct file *file, char __user *user_buf,
+ size_t count, loff_t *ppos)
+{
+ /* Second task waits on mutex, entering uninterruptible sleep */
+ guard(mutex)(&dummy_mutex);
+
+ /* First task sleeps here, interruptible */
+ msleep_interruptible(SLEEP_SECOND * 1000);
+
+ return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+ sizeof(dummy_string));
+}
+
+/* Semaphore-based read function */
+static ssize_t read_dummy_semaphore(struct file *file, char __user *user_buf,
+ size_t count, loff_t *ppos)
+{
+ /* Second task waits on semaphore, entering uninterruptible sleep */
+ down(&dummy_sem);
+
+ /* First task sleeps here, interruptible */
+ msleep_interruptible(SLEEP_SECOND * 1000);
+
+ up(&dummy_sem);
+
+ return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
+ sizeof(dummy_string));
+}
+
+/* File operations for mutex */
+static const struct file_operations hung_task_mutex_fops = {
+ .read = read_dummy_mutex,
+};
+
+/* File operations for semaphore */
+static const struct file_operations hung_task_sem_fops = {
+ .read = read_dummy_semaphore,
+};
+
+static int __init hung_task_tests_init(void)
+{
+ hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
+ if (IS_ERR(hung_task_dir))
+ return PTR_ERR(hung_task_dir);
+
+ /* Create debugfs files for mutex and semaphore tests */
+ debugfs_create_file(HUNG_TASK_MUTEX_FILE, 0400, hung_task_dir, NULL,
+ &hung_task_mutex_fops);
+ debugfs_create_file(HUNG_TASK_SEM_FILE, 0400, hung_task_dir, NULL,
+ &hung_task_sem_fops);
+
+ return 0;
+}
+
+static void __exit hung_task_tests_exit(void)
+{
+ debugfs_remove_recursive(hung_task_dir);
+}
+
+module_init(hung_task_tests_init);
+module_exit(hung_task_tests_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Masami Hiramatsu <mhiramat@kernel.org>");
+MODULE_AUTHOR("Zi Li <amaindex@outlook.com>");
+MODULE_DESCRIPTION("Simple sleep under lock files for testing hung task");
--
2.45.2On Wed, 19 Mar 2025 16:11:38 +0800
Lance Yang <ioworker0@gmail.com> wrote:
> From: Zi Li <amaindex@outlook.com>
>
> Extend the existing hung_task detector test module to support multiple lock
> types, including mutex and semaphore, with room for future additions (e.g.,
> spinlock, etc.). This module creates dummy files under <debugfs>/hung_task,
> such as 'mutex' and 'semaphore'. The read process on any of these files will
> sleep for enough long time (256 seconds) while holding the respective lock.
> As a result, the second process will wait on the lock for a prolonged
> duration and be detected by the hung_task detector.
>
> This change unifies the previous mutex-only sample into a single,
> extensible hung_task_tests module, reducing code duplication and improving
> maintainability.
>
> Usage is:
>
> > cd /sys/kernel/debug/hung_task
> > cat mutex & cat mutex # Test mutex blocking
> > cat semaphore & cat semaphore # Test semaphore blocking
>
> Update the Kconfig description to reflect multiple debugfs files support.
>
This looks good to me. (but have a nit comment below)
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Signed-off-by: Lance Yang <ioworker0@gmail.com>
> Signed-off-by: Zi Li <amaindex@outlook.com>
> ---
> samples/Kconfig | 9 +--
> samples/hung_task/Makefile | 2 +-
> samples/hung_task/hung_task_mutex.c | 66 --------------------
> samples/hung_task/hung_task_tests.c | 97 +++++++++++++++++++++++++++++
> 4 files changed, 103 insertions(+), 71 deletions(-)
> delete mode 100644 samples/hung_task/hung_task_mutex.c
> create mode 100644 samples/hung_task/hung_task_tests.c
>
> diff --git a/samples/Kconfig b/samples/Kconfig
> index 09011be2391a..753ed1f170b5 100644
> --- a/samples/Kconfig
> +++ b/samples/Kconfig
> @@ -304,10 +304,11 @@ config SAMPLE_HUNG_TASK
> tristate "Hung task detector test code"
> depends on DETECT_HUNG_TASK && DEBUG_FS
> help
> - Build a module which provide a simple debugfs file. If user reads
> - the file, it will sleep long time (256 seconds) with holding a
> - mutex. Thus if there are 2 or more processes read this file, it
> - will be detected by the hung_task watchdog.
> + Build a module that provides debugfs files (e.g., mutex, semaphore,
> + etc.) under <debugfs>/hung_task. If user reads one of these files,
> + it will sleep long time (256 seconds) with holding a lock. Thus,
> + if 2 or more processes read the same file concurrently, it will
> + be detected by the hung_task watchdog.
>
> source "samples/rust/Kconfig"
>
> diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
> index fe9dde799880..86036f1a204d 100644
> --- a/samples/hung_task/Makefile
> +++ b/samples/hung_task/Makefile
> @@ -1,2 +1,2 @@
> # SPDX-License-Identifier: GPL-2.0-only
> -obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_mutex.o
> \ No newline at end of file
> +obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_tests.o
> diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_task_mutex.c
> deleted file mode 100644
> index 7a29f2246d22..000000000000
> --- a/samples/hung_task/hung_task_mutex.c
> +++ /dev/null
> @@ -1,66 +0,0 @@
> -// SPDX-License-Identifier: GPL-2.0-or-later
> -/*
> - * hung_task_mutex.c - Sample code which causes hung task by mutex
> - *
> - * Usage: load this module and read `<debugfs>/hung_task/mutex`
> - * by 2 or more processes.
> - *
> - * This is for testing kernel hung_task error message.
> - * Note that this will make your system freeze and maybe
> - * cause panic. So do not use this except for the test.
> - */
> -
> -#include <linux/debugfs.h>
> -#include <linux/delay.h>
> -#include <linux/fs.h>
> -#include <linux/module.h>
> -#include <linux/mutex.h>
> -
> -#define HUNG_TASK_DIR "hung_task"
> -#define HUNG_TASK_FILE "mutex"
> -#define SLEEP_SECOND 256
> -
> -static const char dummy_string[] = "This is a dummy string.";
> -static DEFINE_MUTEX(dummy_mutex);
> -struct dentry *hung_task_dir;
Note that Andrew already fixed this (static)
https://web.git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/samples-add-hung_task-detector-mutex-blocking-sample-fix.patch
Thank you,
> -
> -static ssize_t read_dummy(struct file *file, char __user *user_buf,
> - size_t count, loff_t *ppos)
> -{
> - /* If the second task waits on the lock, it is uninterruptible sleep. */
> - guard(mutex)(&dummy_mutex);
> -
> - /* When the first task sleep here, it is interruptible. */
> - msleep_interruptible(SLEEP_SECOND * 1000);
> -
> - return simple_read_from_buffer(user_buf, count, ppos,
> - dummy_string, sizeof(dummy_string));
> -}
> -
> -static const struct file_operations hung_task_fops = {
> - .read = read_dummy,
> -};
> -
> -static int __init hung_task_sample_init(void)
> -{
> - hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
> - if (IS_ERR(hung_task_dir))
> - return PTR_ERR(hung_task_dir);
> -
> - debugfs_create_file(HUNG_TASK_FILE, 0400, hung_task_dir,
> - NULL, &hung_task_fops);
> -
> - return 0;
> -}
> -
> -static void __exit hung_task_sample_exit(void)
> -{
> - debugfs_remove_recursive(hung_task_dir);
> -}
> -
> -module_init(hung_task_sample_init);
> -module_exit(hung_task_sample_exit);
> -
> -MODULE_LICENSE("GPL");
> -MODULE_AUTHOR("Masami Hiramatsu");
> -MODULE_DESCRIPTION("Simple sleep under mutex file for testing hung task");
> diff --git a/samples/hung_task/hung_task_tests.c b/samples/hung_task/hung_task_tests.c
> new file mode 100644
> index 000000000000..a5c09bd3a47d
> --- /dev/null
> +++ b/samples/hung_task/hung_task_tests.c
> @@ -0,0 +1,97 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * hung_task_tests.c - Sample code for testing hung tasks with mutex,
> + * semaphore, etc.
> + *
> + * Usage: Load this module and read `<debugfs>/hung_task/mutex`,
> + * `<debugfs>/hung_task/semaphore`, etc., with 2 or more processes.
> + *
> + * This is for testing kernel hung_task error messages with various locking
> + * mechanisms (e.g., mutex, semaphore, etc.). Note that this may freeze
> + * your system or cause a panic. Use only for testing purposes.
> + */
> +
> +#include <linux/debugfs.h>
> +#include <linux/delay.h>
> +#include <linux/fs.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/semaphore.h>
> +
> +#define HUNG_TASK_DIR "hung_task"
> +#define HUNG_TASK_MUTEX_FILE "mutex"
> +#define HUNG_TASK_SEM_FILE "semaphore"
> +#define SLEEP_SECOND 256
> +
> +static const char dummy_string[] = "This is a dummy string.";
> +static DEFINE_MUTEX(dummy_mutex);
> +static DEFINE_SEMAPHORE(dummy_sem, 1);
> +static struct dentry *hung_task_dir;
> +
> +/* Mutex-based read function */
> +static ssize_t read_dummy_mutex(struct file *file, char __user *user_buf,
> + size_t count, loff_t *ppos)
> +{
> + /* Second task waits on mutex, entering uninterruptible sleep */
> + guard(mutex)(&dummy_mutex);
> +
> + /* First task sleeps here, interruptible */
> + msleep_interruptible(SLEEP_SECOND * 1000);
> +
> + return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
> + sizeof(dummy_string));
> +}
> +
> +/* Semaphore-based read function */
> +static ssize_t read_dummy_semaphore(struct file *file, char __user *user_buf,
> + size_t count, loff_t *ppos)
> +{
> + /* Second task waits on semaphore, entering uninterruptible sleep */
> + down(&dummy_sem);
> +
> + /* First task sleeps here, interruptible */
> + msleep_interruptible(SLEEP_SECOND * 1000);
> +
> + up(&dummy_sem);
> +
> + return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
> + sizeof(dummy_string));
> +}
> +
> +/* File operations for mutex */
> +static const struct file_operations hung_task_mutex_fops = {
> + .read = read_dummy_mutex,
> +};
> +
> +/* File operations for semaphore */
> +static const struct file_operations hung_task_sem_fops = {
> + .read = read_dummy_semaphore,
> +};
> +
> +static int __init hung_task_tests_init(void)
> +{
> + hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
> + if (IS_ERR(hung_task_dir))
> + return PTR_ERR(hung_task_dir);
> +
> + /* Create debugfs files for mutex and semaphore tests */
> + debugfs_create_file(HUNG_TASK_MUTEX_FILE, 0400, hung_task_dir, NULL,
> + &hung_task_mutex_fops);
> + debugfs_create_file(HUNG_TASK_SEM_FILE, 0400, hung_task_dir, NULL,
> + &hung_task_sem_fops);
> +
> + return 0;
> +}
> +
> +static void __exit hung_task_tests_exit(void)
> +{
> + debugfs_remove_recursive(hung_task_dir);
> +}
> +
> +module_init(hung_task_tests_init);
> +module_exit(hung_task_tests_exit);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Masami Hiramatsu <mhiramat@kernel.org>");
> +MODULE_AUTHOR("Zi Li <amaindex@outlook.com>");
> +MODULE_DESCRIPTION("Simple sleep under lock files for testing hung task");
> --
> 2.45.2
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
On Wed, Mar 19, 2025 at 9:49 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Wed, 19 Mar 2025 16:11:38 +0800
> Lance Yang <ioworker0@gmail.com> wrote:
>
> > From: Zi Li <amaindex@outlook.com>
> >
> > Extend the existing hung_task detector test module to support multiple lock
> > types, including mutex and semaphore, with room for future additions (e.g.,
> > spinlock, etc.). This module creates dummy files under <debugfs>/hung_task,
> > such as 'mutex' and 'semaphore'. The read process on any of these files will
> > sleep for enough long time (256 seconds) while holding the respective lock.
> > As a result, the second process will wait on the lock for a prolonged
> > duration and be detected by the hung_task detector.
> >
> > This change unifies the previous mutex-only sample into a single,
> > extensible hung_task_tests module, reducing code duplication and improving
> > maintainability.
> >
> > Usage is:
> >
> > > cd /sys/kernel/debug/hung_task
> > > cat mutex & cat mutex # Test mutex blocking
> > > cat semaphore & cat semaphore # Test semaphore blocking
> >
> > Update the Kconfig description to reflect multiple debugfs files support.
> >
>
> This looks good to me. (but have a nit comment below)
>
> Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Thanks a lot for taking time to review!
>
> > Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > Signed-off-by: Lance Yang <ioworker0@gmail.com>
> > Signed-off-by: Zi Li <amaindex@outlook.com>
> > ---
> > samples/Kconfig | 9 +--
> > samples/hung_task/Makefile | 2 +-
> > samples/hung_task/hung_task_mutex.c | 66 --------------------
> > samples/hung_task/hung_task_tests.c | 97 +++++++++++++++++++++++++++++
> > 4 files changed, 103 insertions(+), 71 deletions(-)
> > delete mode 100644 samples/hung_task/hung_task_mutex.c
> > create mode 100644 samples/hung_task/hung_task_tests.c
> >
> > diff --git a/samples/Kconfig b/samples/Kconfig
> > index 09011be2391a..753ed1f170b5 100644
> > --- a/samples/Kconfig
> > +++ b/samples/Kconfig
> > @@ -304,10 +304,11 @@ config SAMPLE_HUNG_TASK
> > tristate "Hung task detector test code"
> > depends on DETECT_HUNG_TASK && DEBUG_FS
> > help
> > - Build a module which provide a simple debugfs file. If user reads
> > - the file, it will sleep long time (256 seconds) with holding a
> > - mutex. Thus if there are 2 or more processes read this file, it
> > - will be detected by the hung_task watchdog.
> > + Build a module that provides debugfs files (e.g., mutex, semaphore,
> > + etc.) under <debugfs>/hung_task. If user reads one of these files,
> > + it will sleep long time (256 seconds) with holding a lock. Thus,
> > + if 2 or more processes read the same file concurrently, it will
> > + be detected by the hung_task watchdog.
> >
> > source "samples/rust/Kconfig"
> >
> > diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
> > index fe9dde799880..86036f1a204d 100644
> > --- a/samples/hung_task/Makefile
> > +++ b/samples/hung_task/Makefile
> > @@ -1,2 +1,2 @@
> > # SPDX-License-Identifier: GPL-2.0-only
> > -obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_mutex.o
> > \ No newline at end of file
> > +obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_tests.o
> > diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_task_mutex.c
> > deleted file mode 100644
> > index 7a29f2246d22..000000000000
> > --- a/samples/hung_task/hung_task_mutex.c
> > +++ /dev/null
> > @@ -1,66 +0,0 @@
> > -// SPDX-License-Identifier: GPL-2.0-or-later
> > -/*
> > - * hung_task_mutex.c - Sample code which causes hung task by mutex
> > - *
> > - * Usage: load this module and read `<debugfs>/hung_task/mutex`
> > - * by 2 or more processes.
> > - *
> > - * This is for testing kernel hung_task error message.
> > - * Note that this will make your system freeze and maybe
> > - * cause panic. So do not use this except for the test.
> > - */
> > -
> > -#include <linux/debugfs.h>
> > -#include <linux/delay.h>
> > -#include <linux/fs.h>
> > -#include <linux/module.h>
> > -#include <linux/mutex.h>
> > -
> > -#define HUNG_TASK_DIR "hung_task"
> > -#define HUNG_TASK_FILE "mutex"
> > -#define SLEEP_SECOND 256
> > -
> > -static const char dummy_string[] = "This is a dummy string.";
> > -static DEFINE_MUTEX(dummy_mutex);
> > -struct dentry *hung_task_dir;
>
> Note that Andrew already fixed this (static)
>
> https://web.git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/samples-add-hung_task-detector-mutex-blocking-sample-fix.patch
Good catch! I’ll rebase this patch on that.
Thanks again for your time!
Lance
>
> Thank you,
>
> > -
> > -static ssize_t read_dummy(struct file *file, char __user *user_buf,
> > - size_t count, loff_t *ppos)
> > -{
> > - /* If the second task waits on the lock, it is uninterruptible sleep. */
> > - guard(mutex)(&dummy_mutex);
> > -
> > - /* When the first task sleep here, it is interruptible. */
> > - msleep_interruptible(SLEEP_SECOND * 1000);
> > -
> > - return simple_read_from_buffer(user_buf, count, ppos,
> > - dummy_string, sizeof(dummy_string));
> > -}
> > -
> > -static const struct file_operations hung_task_fops = {
> > - .read = read_dummy,
> > -};
> > -
> > -static int __init hung_task_sample_init(void)
> > -{
> > - hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
> > - if (IS_ERR(hung_task_dir))
> > - return PTR_ERR(hung_task_dir);
> > -
> > - debugfs_create_file(HUNG_TASK_FILE, 0400, hung_task_dir,
> > - NULL, &hung_task_fops);
> > -
> > - return 0;
> > -}
> > -
> > -static void __exit hung_task_sample_exit(void)
> > -{
> > - debugfs_remove_recursive(hung_task_dir);
> > -}
> > -
> > -module_init(hung_task_sample_init);
> > -module_exit(hung_task_sample_exit);
> > -
> > -MODULE_LICENSE("GPL");
> > -MODULE_AUTHOR("Masami Hiramatsu");
> > -MODULE_DESCRIPTION("Simple sleep under mutex file for testing hung task");
> > diff --git a/samples/hung_task/hung_task_tests.c b/samples/hung_task/hung_task_tests.c
> > new file mode 100644
> > index 000000000000..a5c09bd3a47d
> > --- /dev/null
> > +++ b/samples/hung_task/hung_task_tests.c
> > @@ -0,0 +1,97 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * hung_task_tests.c - Sample code for testing hung tasks with mutex,
> > + * semaphore, etc.
> > + *
> > + * Usage: Load this module and read `<debugfs>/hung_task/mutex`,
> > + * `<debugfs>/hung_task/semaphore`, etc., with 2 or more processes.
> > + *
> > + * This is for testing kernel hung_task error messages with various locking
> > + * mechanisms (e.g., mutex, semaphore, etc.). Note that this may freeze
> > + * your system or cause a panic. Use only for testing purposes.
> > + */
> > +
> > +#include <linux/debugfs.h>
> > +#include <linux/delay.h>
> > +#include <linux/fs.h>
> > +#include <linux/module.h>
> > +#include <linux/mutex.h>
> > +#include <linux/semaphore.h>
> > +
> > +#define HUNG_TASK_DIR "hung_task"
> > +#define HUNG_TASK_MUTEX_FILE "mutex"
> > +#define HUNG_TASK_SEM_FILE "semaphore"
> > +#define SLEEP_SECOND 256
> > +
> > +static const char dummy_string[] = "This is a dummy string.";
> > +static DEFINE_MUTEX(dummy_mutex);
> > +static DEFINE_SEMAPHORE(dummy_sem, 1);
> > +static struct dentry *hung_task_dir;
> > +
> > +/* Mutex-based read function */
> > +static ssize_t read_dummy_mutex(struct file *file, char __user *user_buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + /* Second task waits on mutex, entering uninterruptible sleep */
> > + guard(mutex)(&dummy_mutex);
> > +
> > + /* First task sleeps here, interruptible */
> > + msleep_interruptible(SLEEP_SECOND * 1000);
> > +
> > + return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
> > + sizeof(dummy_string));
> > +}
> > +
> > +/* Semaphore-based read function */
> > +static ssize_t read_dummy_semaphore(struct file *file, char __user *user_buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + /* Second task waits on semaphore, entering uninterruptible sleep */
> > + down(&dummy_sem);
> > +
> > + /* First task sleeps here, interruptible */
> > + msleep_interruptible(SLEEP_SECOND * 1000);
> > +
> > + up(&dummy_sem);
> > +
> > + return simple_read_from_buffer(user_buf, count, ppos, dummy_string,
> > + sizeof(dummy_string));
> > +}
> > +
> > +/* File operations for mutex */
> > +static const struct file_operations hung_task_mutex_fops = {
> > + .read = read_dummy_mutex,
> > +};
> > +
> > +/* File operations for semaphore */
> > +static const struct file_operations hung_task_sem_fops = {
> > + .read = read_dummy_semaphore,
> > +};
> > +
> > +static int __init hung_task_tests_init(void)
> > +{
> > + hung_task_dir = debugfs_create_dir(HUNG_TASK_DIR, NULL);
> > + if (IS_ERR(hung_task_dir))
> > + return PTR_ERR(hung_task_dir);
> > +
> > + /* Create debugfs files for mutex and semaphore tests */
> > + debugfs_create_file(HUNG_TASK_MUTEX_FILE, 0400, hung_task_dir, NULL,
> > + &hung_task_mutex_fops);
> > + debugfs_create_file(HUNG_TASK_SEM_FILE, 0400, hung_task_dir, NULL,
> > + &hung_task_sem_fops);
> > +
> > + return 0;
> > +}
> > +
> > +static void __exit hung_task_tests_exit(void)
> > +{
> > + debugfs_remove_recursive(hung_task_dir);
> > +}
> > +
> > +module_init(hung_task_tests_init);
> > +module_exit(hung_task_tests_exit);
> > +
> > +MODULE_LICENSE("GPL");
> > +MODULE_AUTHOR("Masami Hiramatsu <mhiramat@kernel.org>");
> > +MODULE_AUTHOR("Zi Li <amaindex@outlook.com>");
> > +MODULE_DESCRIPTION("Simple sleep under lock files for testing hung task");
> > --
> > 2.45.2
> >
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>
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