[v4] hung_task: Dump the blocking task stacktrace

[PATCH v4 2/2] samples: Add hung_task detector mutex blocking sample

Posted by Masami Hiramatsu (Google) 9 months, 3 weeks ago

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add a hung_task detector mutex blocking test sample code.

This module will create a dummy file on the debugfs. That file will
cause the read process to sleep for enough long time (256 seconds)
while holding a mutex. As a result, the second process will wait on
the mutex for a prolonged duration and be detected by the hung_task
detector.

Usage is;

 > cd /sys/kernel/debug/hung_task
 > cat mutex & cat mutex

and wait for hung_task message.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 samples/Kconfig                     |    9 +++++
 samples/Makefile                    |    1 +
 samples/hung_task/Makefile          |    2 +
 samples/hung_task/hung_task_mutex.c |   66 +++++++++++++++++++++++++++++++++++
 4 files changed, 78 insertions(+)
 create mode 100644 samples/hung_task/Makefile
 create mode 100644 samples/hung_task/hung_task_mutex.c

diff --git a/samples/Kconfig b/samples/Kconfig
index 820e00b2ed68..09011be2391a 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -300,6 +300,15 @@ config SAMPLE_CHECK_EXEC
 	  demonstrate how they should be used with execveat(2) +
 	  AT_EXECVE_CHECK.
 
+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.
+
 source "samples/rust/Kconfig"
 
 source "samples/damon/Kconfig"
diff --git a/samples/Makefile b/samples/Makefile
index f24cd0d72dd0..bf6e6fca5410 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -42,3 +42,4 @@ obj-$(CONFIG_SAMPLE_FPROBE)		+= fprobe/
 obj-$(CONFIG_SAMPLES_RUST)		+= rust/
 obj-$(CONFIG_SAMPLE_DAMON_WSSE)		+= damon/
 obj-$(CONFIG_SAMPLE_DAMON_PRCL)		+= damon/
+obj-$(CONFIG_SAMPLE_HUNG_TASK)		+= hung_task/
diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
new file mode 100644
index 000000000000..fe9dde799880
--- /dev/null
+++ b/samples/hung_task/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_mutex.o
\ No newline at end of file
diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_task_mutex.c
new file mode 100644
index 000000000000..7a29f2246d22
--- /dev/null
+++ b/samples/hung_task/hung_task_mutex.c
@@ -0,0 +1,66 @@
+// 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");

Re: [PATCH v4 2/2] samples: Add hung_task detector mutex blocking sample

Posted by Lance Yang 9 months, 3 weeks ago

On Tue, Feb 25, 2025 at 3:02 PM Masami Hiramatsu (Google)
<mhiramat@kernel.org> wrote:
>
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> Add a hung_task detector mutex blocking test sample code.
>
> This module will create a dummy file on the debugfs. That file will
> cause the read process to sleep for enough long time (256 seconds)
> while holding a mutex. As a result, the second process will wait on
> the mutex for a prolonged duration and be detected by the hung_task
> detector.
>
> Usage is;
>
>  > cd /sys/kernel/debug/hung_task
>  > cat mutex & cat mutex
>
> and wait for hung_task message.
>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
>  samples/Kconfig                     |    9 +++++
>  samples/Makefile                    |    1 +
>  samples/hung_task/Makefile          |    2 +
>  samples/hung_task/hung_task_mutex.c |   66 +++++++++++++++++++++++++++++++++++
>  4 files changed, 78 insertions(+)
>  create mode 100644 samples/hung_task/Makefile
>  create mode 100644 samples/hung_task/hung_task_mutex.c
>
> diff --git a/samples/Kconfig b/samples/Kconfig
> index 820e00b2ed68..09011be2391a 100644
> --- a/samples/Kconfig
> +++ b/samples/Kconfig
> @@ -300,6 +300,15 @@ config SAMPLE_CHECK_EXEC
>           demonstrate how they should be used with execveat(2) +
>           AT_EXECVE_CHECK.
>
> +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.
> +
>  source "samples/rust/Kconfig"

I'm just wondering if we should also make the SAMPLE_HUNG_TASK
depend on !PREEMPT_RT for now?

Thanks,
Lance

>
>  source "samples/damon/Kconfig"
> diff --git a/samples/Makefile b/samples/Makefile
> index f24cd0d72dd0..bf6e6fca5410 100644
> --- a/samples/Makefile
> +++ b/samples/Makefile
> @@ -42,3 +42,4 @@ obj-$(CONFIG_SAMPLE_FPROBE)           += fprobe/
>  obj-$(CONFIG_SAMPLES_RUST)             += rust/
>  obj-$(CONFIG_SAMPLE_DAMON_WSSE)                += damon/
>  obj-$(CONFIG_SAMPLE_DAMON_PRCL)                += damon/
> +obj-$(CONFIG_SAMPLE_HUNG_TASK)         += hung_task/
> diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
> new file mode 100644
> index 000000000000..fe9dde799880
> --- /dev/null
> +++ b/samples/hung_task/Makefile
> @@ -0,0 +1,2 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_mutex.o
> \ No newline at end of file
> diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_task_mutex.c
> new file mode 100644
> index 000000000000..7a29f2246d22
> --- /dev/null
> +++ b/samples/hung_task/hung_task_mutex.c
> @@ -0,0 +1,66 @@
> +// 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");
>

Re: [PATCH v4 2/2] samples: Add hung_task detector mutex blocking sample

Posted by Masami Hiramatsu (Google) 9 months, 3 weeks ago

On Wed, 26 Feb 2025 09:50:32 +0800
Lance Yang <ioworker0@gmail.com> wrote:

> On Tue, Feb 25, 2025 at 3:02 PM Masami Hiramatsu (Google)
> <mhiramat@kernel.org> wrote:
> >
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> >
> > Add a hung_task detector mutex blocking test sample code.
> >
> > This module will create a dummy file on the debugfs. That file will
> > cause the read process to sleep for enough long time (256 seconds)
> > while holding a mutex. As a result, the second process will wait on
> > the mutex for a prolonged duration and be detected by the hung_task
> > detector.
> >
> > Usage is;
> >
> >  > cd /sys/kernel/debug/hung_task
> >  > cat mutex & cat mutex
> >
> > and wait for hung_task message.
> >
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > ---
> >  samples/Kconfig                     |    9 +++++
> >  samples/Makefile                    |    1 +
> >  samples/hung_task/Makefile          |    2 +
> >  samples/hung_task/hung_task_mutex.c |   66 +++++++++++++++++++++++++++++++++++
> >  4 files changed, 78 insertions(+)
> >  create mode 100644 samples/hung_task/Makefile
> >  create mode 100644 samples/hung_task/hung_task_mutex.c
> >
> > diff --git a/samples/Kconfig b/samples/Kconfig
> > index 820e00b2ed68..09011be2391a 100644
> > --- a/samples/Kconfig
> > +++ b/samples/Kconfig
> > @@ -300,6 +300,15 @@ config SAMPLE_CHECK_EXEC
> >           demonstrate how they should be used with execveat(2) +
> >           AT_EXECVE_CHECK.
> >
> > +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.
> > +
> >  source "samples/rust/Kconfig"
> 
> I'm just wondering if we should also make the SAMPLE_HUNG_TASK
> depend on !PREEMPT_RT for now?

Yeah, I also have a question. This does not check the blocker,
but just providing the testing interface with mutex. So there is
no direct connection with DETECT_HUNG_TASK_BLOCKER. Thus I didn't
add the dependency.

Thank you,

> 
> Thanks,
> Lance
> 
> >
> >  source "samples/damon/Kconfig"
> > diff --git a/samples/Makefile b/samples/Makefile
> > index f24cd0d72dd0..bf6e6fca5410 100644
> > --- a/samples/Makefile
> > +++ b/samples/Makefile
> > @@ -42,3 +42,4 @@ obj-$(CONFIG_SAMPLE_FPROBE)           += fprobe/
> >  obj-$(CONFIG_SAMPLES_RUST)             += rust/
> >  obj-$(CONFIG_SAMPLE_DAMON_WSSE)                += damon/
> >  obj-$(CONFIG_SAMPLE_DAMON_PRCL)                += damon/
> > +obj-$(CONFIG_SAMPLE_HUNG_TASK)         += hung_task/
> > diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
> > new file mode 100644
> > index 000000000000..fe9dde799880
> > --- /dev/null
> > +++ b/samples/hung_task/Makefile
> > @@ -0,0 +1,2 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_mutex.o
> > \ No newline at end of file
> > diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_task_mutex.c
> > new file mode 100644
> > index 000000000000..7a29f2246d22
> > --- /dev/null
> > +++ b/samples/hung_task/hung_task_mutex.c
> > @@ -0,0 +1,66 @@
> > +// 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");
> >


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH v4 2/2] samples: Add hung_task detector mutex blocking sample

Posted by Lance Yang 9 months, 3 weeks ago

On Wed, Feb 26, 2025 at 3:04 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> On Wed, 26 Feb 2025 09:50:32 +0800
> Lance Yang <ioworker0@gmail.com> wrote:
>
> > On Tue, Feb 25, 2025 at 3:02 PM Masami Hiramatsu (Google)
> > <mhiramat@kernel.org> wrote:
> > >
> > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > >
> > > Add a hung_task detector mutex blocking test sample code.
> > >
> > > This module will create a dummy file on the debugfs. That file will
> > > cause the read process to sleep for enough long time (256 seconds)
> > > while holding a mutex. As a result, the second process will wait on
> > > the mutex for a prolonged duration and be detected by the hung_task
> > > detector.
> > >
> > > Usage is;
> > >
> > >  > cd /sys/kernel/debug/hung_task
> > >  > cat mutex & cat mutex
> > >
> > > and wait for hung_task message.
> > >
> > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > ---
> > >  samples/Kconfig                     |    9 +++++
> > >  samples/Makefile                    |    1 +
> > >  samples/hung_task/Makefile          |    2 +
> > >  samples/hung_task/hung_task_mutex.c |   66 +++++++++++++++++++++++++++++++++++
> > >  4 files changed, 78 insertions(+)
> > >  create mode 100644 samples/hung_task/Makefile
> > >  create mode 100644 samples/hung_task/hung_task_mutex.c
> > >
> > > diff --git a/samples/Kconfig b/samples/Kconfig
> > > index 820e00b2ed68..09011be2391a 100644
> > > --- a/samples/Kconfig
> > > +++ b/samples/Kconfig
> > > @@ -300,6 +300,15 @@ config SAMPLE_CHECK_EXEC
> > >           demonstrate how they should be used with execveat(2) +
> > >           AT_EXECVE_CHECK.
> > >
> > > +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.
> > > +
> > >  source "samples/rust/Kconfig"
> >
> > I'm just wondering if we should also make the SAMPLE_HUNG_TASK
> > depend on !PREEMPT_RT for now?
>
> Yeah, I also have a question. This does not check the blocker,
> but just providing the testing interface with mutex. So there is
> no direct connection with DETECT_HUNG_TASK_BLOCKER. Thus I didn't
> add the dependency.

Yep, whether we add it or not is not a big deal ;)

Thanks,
Lance

>
> Thank you,
>
> >
> > Thanks,
> > Lance
> >
> > >
> > >  source "samples/damon/Kconfig"
> > > diff --git a/samples/Makefile b/samples/Makefile
> > > index f24cd0d72dd0..bf6e6fca5410 100644
> > > --- a/samples/Makefile
> > > +++ b/samples/Makefile
> > > @@ -42,3 +42,4 @@ obj-$(CONFIG_SAMPLE_FPROBE)           += fprobe/
> > >  obj-$(CONFIG_SAMPLES_RUST)             += rust/
> > >  obj-$(CONFIG_SAMPLE_DAMON_WSSE)                += damon/
> > >  obj-$(CONFIG_SAMPLE_DAMON_PRCL)                += damon/
> > > +obj-$(CONFIG_SAMPLE_HUNG_TASK)         += hung_task/
> > > diff --git a/samples/hung_task/Makefile b/samples/hung_task/Makefile
> > > new file mode 100644
> > > index 000000000000..fe9dde799880
> > > --- /dev/null
> > > +++ b/samples/hung_task/Makefile
> > > @@ -0,0 +1,2 @@
> > > +# SPDX-License-Identifier: GPL-2.0-only
> > > +obj-$(CONFIG_SAMPLE_HUNG_TASK) += hung_task_mutex.o
> > > \ No newline at end of file
> > > diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_task_mutex.c
> > > new file mode 100644
> > > index 000000000000..7a29f2246d22
> > > --- /dev/null
> > > +++ b/samples/hung_task/hung_task_mutex.c
> > > @@ -0,0 +1,66 @@
> > > +// 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");
> > >
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@kernel.org>

[PATCH v4 1/2] hung_task: Show the blocker task if the task is hung on mutex
[PATCH v4 2/2] samples: Add hung_task detector mutex blocking sample