linux-kernel - [PATCH 1/2] hung_task: Consolidate hung task warning into an atomic log block

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Message-ID: <20251209041218.1583600-2-atomlin@atomlin.com>
Date: Mon,  8 Dec 2025 23:12:17 -0500
From: Aaron Tomlin <atomlin@...mlin.com>
To: akpm@...ux-foundation.org,
	lance.yang@...ux.dev,
	mhiramat@...nel.org,
	gregkh@...uxfoundation.org
Cc: sean@...e.io,
	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] hung_task: Consolidate hung task warning into an atomic log block

Consolidate the multi-line console output in check_hung_task() into a new
helper function, hung_task_diagnostics().

This patch ensures the entire diagnostic block (task info, kernel
version, and sysctl advice) is logged to the ring buffer via a single
pr_err() call. This is critical in a concurrent environment to prevent
message lines from interleaving with other CPU activity, thus
maintaining contextual integrity of the warning message.

Signed-off-by: Aaron Tomlin <atomlin@...mlin.com>
---
 kernel/hung_task.c | 37 +++++++++++++++++++++++++++----------
 1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index d2254c91450b..d5109a0994c5 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -223,6 +223,32 @@ static inline void debug_show_blocker(struct task_struct *task, unsigned long ti
 }
 #endif
 
+/**
+ * hung_task_diagnostics - Print structured diagnostic info for a hung task.
+ * @t: The struct task_struct of the detected hung task.
+ *
+ * This function consolidates the printing of core diagnostic information
+ * for a task found to be blocked. This approach ensures atomic logging
+ * of the multi-line message block, preventing interleaving by other
+ * console activity, thus maintaining contextual clarity.
+ */
+static void hung_task_diagnostics(struct task_struct *t)
+{
+	unsigned long blocked_secs = (jiffies - t->last_switch_time) / HZ;
+
+	pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n"
+	       "      %s %s %.*s\n"
+	       "%s\n"
+	       "\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
+	       " disables this message.\n",
+	       t->comm, t->pid, blocked_secs,
+	       print_tainted(), init_utsname()->release,
+	       (int)strcspn(init_utsname()->version, " "),
+	       init_utsname()->version,
+	       (t->flags & PF_POSTCOREDUMP) ?
+	       "      Blocked by coredump." : "");
+}
+
 static void check_hung_task(struct task_struct *t, unsigned long timeout,
 		unsigned long prev_detect_count)
 {
@@ -252,16 +278,7 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout,
 	if (sysctl_hung_task_warnings || hung_task_call_panic) {
 		if (sysctl_hung_task_warnings > 0)
 			sysctl_hung_task_warnings--;
-		pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
-		       t->comm, t->pid, (jiffies - t->last_switch_time) / HZ);
-		pr_err("      %s %s %.*s\n",
-			print_tainted(), init_utsname()->release,
-			(int)strcspn(init_utsname()->version, " "),
-			init_utsname()->version);
-		if (t->flags & PF_POSTCOREDUMP)
-			pr_err("      Blocked by coredump.\n");
-		pr_err("\"echo 0 > /proc/sys/kernel/hung_task_timeout_secs\""
-			" disables this message.\n");
+		hung_task_diagnostics(t);
 		sched_show_task(t);
 		debug_show_blocker(t, timeout);
 
-- 
2.51.0