linux-kernel - [PATCH RFC 06/12] watchdog: Allow runtime toggle of hardlockup detector on CPUs

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Message-Id: <20260206-feature-dynamic_isolcpus_dhei-v1-6-00a711eb0c74@gmail.com>
Date: Fri, 06 Feb 2026 02:04:27 -0500
From: Qiliang Yuan <realwujing@...il.com>
To: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, 
 Juri Lelli <juri.lelli@...hat.com>, 
 Vincent Guittot <vincent.guittot@...aro.org>, 
 Dietmar Eggemann <dietmar.eggemann@....com>, 
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, 
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, 
 Thomas Gleixner <tglx@...nel.org>, "Paul E. McKenney" <paulmck@...nel.org>, 
 Frederic Weisbecker <frederic@...nel.org>, 
 Neeraj Upadhyay <neeraj.upadhyay@...nel.org>, 
 Joel Fernandes <joelagnelf@...dia.com>, 
 Josh Triplett <josh@...htriplett.org>, Boqun Feng <boqun.feng@...il.com>, 
 Uladzislau Rezki <urezki@...il.com>, 
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, 
 Lai Jiangshan <jiangshanlai@...il.com>, Zqiang <qiang.zhang@...ux.dev>, 
 Tejun Heo <tj@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
 Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>, 
 Michal Hocko <mhocko@...e.com>, Brendan Jackman <jackmanb@...gle.com>, 
 Johannes Weiner <hannes@...xchg.org>, Zi Yan <ziy@...dia.com>, 
 Anna-Maria Behnsen <anna-maria@...utronix.de>, 
 Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, rcu@...r.kernel.org, linux-mm@...ck.org, 
 Qiliang Yuan <realwujing@...il.com>, Qiliang Yuan <yuanql9@...natelecom.cn>
Subject: [PATCH RFC 06/12] watchdog: Allow runtime toggle of hardlockup
 detector on CPUs

The lockup detector (watchdog) affinity is initially set based on the
HK_TYPE_TIMER housekeeping mask. However, if this mask is updated at
runtime, the watchdog threads remain on their original CPUs.

Register a housekeeping notifier to update watchdog_cpumask and trigger
a reconfiguration via proc_watchdog_update() when the HK_TYPE_TIMER
housekeeping mask changes. This ensures that watchdog threads are
synchronized with the new isolation boundaries.

Signed-off-by: Qiliang Yuan <realwujing@...il.com>
Signed-off-by: Qiliang Yuan <yuanql9@...natelecom.cn>
---
 kernel/watchdog.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 366122f4a0f8..2922d7f93d61 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -26,6 +26,7 @@
 #include <linux/sysctl.h>
 #include <linux/tick.h>
 #include <linux/sys_info.h>
+#include <linux/sched/isolation.h>

 #include <linux/sched/clock.h>
 #include <linux/sched/debug.h>
@@ -1359,6 +1360,28 @@ static int __init lockup_detector_check(void)
 }
 late_initcall_sync(lockup_detector_check);

+static int watchdog_housekeeping_reconfigure(struct notifier_block *nb,
+					    unsigned long action, void *data)
+{
+	if (action == HK_UPDATE_MASK) {
+		unsigned int type = (unsigned long)data;
+
+		if (type == HK_TYPE_TIMER) {
+			mutex_lock(&watchdog_mutex);
+			cpumask_copy(&watchdog_cpumask,
+				     housekeeping_cpumask(HK_TYPE_TIMER));
+			proc_watchdog_update(false);
+			mutex_unlock(&watchdog_mutex);
+		}
+	}
+
+	return NOTIFY_OK;
+}
+
+static struct notifier_block watchdog_housekeeping_nb = {
+	.notifier_call = watchdog_housekeeping_reconfigure,
+};
+
 void __init lockup_detector_init(void)
 {
 	if (tick_nohz_full_enabled())
@@ -1373,4 +1396,5 @@ void __init lockup_detector_init(void)
 		allow_lockup_detector_init_retry = true;

 	lockup_detector_setup();
+	housekeeping_register_notifier(&watchdog_housekeeping_nb);
 }

-- 
2.51.0