Introduce support for writing to /proc/sys/kernel/hung_task_detect_count.

Writing any value to this file atomically resets the counter of detected
hung tasks to zero. This grants system administrators the ability to clear
the cumulative diagnostic history after resolving an incident, simplifying
monitoring without requiring a system restart.

Signed-off-by: Aaron Tomlin <atomlin@atomlin.com>
---
 Documentation/admin-guide/sysctl/kernel.rst |  2 +-
 kernel/hung_task.c                          | 29 +++++++++++++++++++--
 2 files changed, 28 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 239da22c4e28..43c17b919969 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -418,7 +418,7 @@ hung_task_detect_count
 ======================
 
 Indicates the total number of tasks that have been detected as hung since
-the system boot.
+the system boot. The counter can be reset to zero when written to.
 
 This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
 
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 5902573200c0..01ce46a107b0 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -375,6 +375,31 @@ static long hung_timeout_jiffies(unsigned long last_checked,
 }
 
 #ifdef CONFIG_SYSCTL
+
+/**
+ * proc_dohung_task_detect_count - proc handler for hung_task_detect_count
+ * @table: Pointer to the struct ctl_table definition for this proc entry
+ * @write: Flag indicating the operation
+ * @buffer: User space buffer for data transfer
+ * @lenp: Pointer to the length of the data being transferred
+ * @ppos: Pointer to the current file offset
+ *
+ * This handler is used for reading the current hung task detection count
+ * and for resetting it to zero when a write operation is performed.
+ * Returns 0 on success or a negative error code on failure.
+ */
+static int proc_dohung_task_detect_count(const struct ctl_table *table, int write,
+					 void *buffer, size_t *lenp, loff_t *ppos)
+{
+	if (!write)
+		return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
+
+	WRITE_ONCE(sysctl_hung_task_detect_count, 0);
+	*ppos += *lenp;
+
+	return 0;
+}
+
 /*
  * Process updating of timeout sysctl
  */
@@ -457,8 +482,8 @@ static const struct ctl_table hung_task_sysctls[] = {
 		.procname	= "hung_task_detect_count",
 		.data		= &sysctl_hung_task_detect_count,
 		.maxlen		= sizeof(unsigned long),
-		.mode		= 0444,
-		.proc_handler	= proc_doulongvec_minmax,
+		.mode		= 0644,
+		.proc_handler	= proc_dohung_task_detect_count,
 	},
 	{
 		.procname	= "hung_task_sys_info",
-- 
2.51.0