1 files changed, 66 insertions, 0 deletions
diff --git a/samples/hung_task/hung_task_mutex.c b/samples/hung_task/hung_task_mutex.c
new file mode 100644
index 000000000000..47ed38239ea3
--- /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);
+static 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");