Re: [PATCH v5 07/12] watchdog: Sync watchdog_cpumask with HK_TYPE_KERNEL_NOISE on isolation

[Bradley Morgan]

On 2 October 2026 14:10:27 BST, Qiliang Yuan <odys.yuan@xxxxxxxxx> wrote:
>The watchdog is initialized at boot to run on all housekeeping CPUs
>(HK_TYPE_KERNEL_NOISE). When a cpuset isolated partition removes CPUs
>from that mask at runtime, watchdog continues running on those CPUs
>because nothing updates watchdog_cpumask.
>
>Save the boot-time watchdog_cpumask as watchdog_cpumask_boot, which
>captures the user's intended coverage (possibly narrowed via kernel
>parameter or sysctl) before any runtime isolation. Introduce
>lockup_detector_hk_update() which intersects this boot snapshot with
>the current HK_TYPE_KERNEL_NOISE mask and reconfigures the detector.
>This ensures that isolated CPUs are excluded while honoring any
>manual narrowing the admin applied at or after boot.
>
>lockup_detector_hk_update() snapshots the RCU-protected housekeeping
>mask under rcu_read_lock(), then updates watchdog_cpumask and calls
>__lockup_detector_reconfigure() under watchdog_mutex, matching the
>same locking discipline used by proc_watchdog_cpumask().
>

Added Petr mladek, maybe he may be interested? See comments:

>Signed-off-by: Qiliang Yuan <odys.yuan@xxxxxxxxx>
>---
> include/linux/nmi.h |  2 ++
> kernel/watchdog.c   | 24 ++++++++++++++++++++++++
> 2 files changed, 26 insertions(+)
>
>diff --git a/include/linux/nmi.h b/include/linux/nmi.h
>index af69712df5f48..409af7884d939 100644
>--- a/include/linux/nmi.h
>+++ b/include/linux/nmi.h
>@@ -37,6 +37,7 @@ extern int sysctl_hardlockup_all_cpu_backtrace;
> static inline void lockup_detector_init(void) { }
> static inline void lockup_detector_retry_init(void) { }
> static inline void lockup_detector_soft_poweroff(void) { }
>+static inline void lockup_detector_hk_update(void) { }
> #endif /* !CONFIG_LOCKUP_DETECTOR */
> 
> #ifdef CONFIG_SOFTLOCKUP_DETECTOR
>@@ -120,6 +121,7 @@ void watchdog_hardlockup_enable(unsigned int cpu);
> void watchdog_hardlockup_disable(unsigned int cpu);
> 
> void lockup_detector_reconfigure(void);
>+void lockup_detector_hk_update(void);
> 
> #ifdef CONFIG_HARDLOCKUP_DETECTOR_BUDDY
> void watchdog_buddy_check_hardlockup(int hrtimer_interrupts);
>diff --git a/kernel/watchdog.c b/kernel/watchdog.c
>index e567fbb0d4692..d4eccb8e337f1 100644
>--- a/kernel/watchdog.c
>+++ b/kernel/watchdog.c
>@@ -53,6 +53,8 @@ static int __read_mostly watchdog_hardlockup_available;
> 
> struct cpumask watchdog_cpumask __read_mostly;
> unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);
>+/* Boot snapshot: user's intended watchdog mask before any runtime isolation. */
>+static struct cpumask watchdog_cpumask_boot __ro_after_init;
> 
> #ifdef CONFIG_HARDLOCKUP_DETECTOR
> 
>@@ -1348,6 +1350,27 @@ static void __init lockup_detector_delay_init(struct work_struct *work)
> 	lockup_detector_setup();
> }
> 

Why no comment?, other than that,

Looks good to me, cheerss

Reviewed-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>

>+void lockup_detector_hk_update(void)
>+{
>+	cpumask_var_t new_mask;
>+
>+	if (!alloc_cpumask_var(&new_mask, GFP_KERNEL))
>+		return;
>+
>+	rcu_read_lock();
>+	cpumask_and(new_mask, &watchdog_cpumask_boot,
>+		    housekeeping_cpumask_rcu(HK_TYPE_KERNEL_NOISE));
>+	rcu_read_unlock();
>+
>+	mutex_lock(&watchdog_mutex);
>+	cpumask_copy(&watchdog_cpumask, new_mask);
>+	__lockup_detector_reconfigure(false);
>+	mutex_unlock(&watchdog_mutex);
>+
>+	free_cpumask_var(new_mask);
>+}
>+EXPORT_SYMBOL_GPL(lockup_detector_hk_update);
>+
> /*
>  * lockup_detector_retry_init - retry init lockup detector if possible.
>  *
>@@ -1390,6 +1413,7 @@ void __init lockup_detector_init(void)
> 
> 	cpumask_copy(&watchdog_cpumask,
> 		     housekeeping_cpumask(HK_TYPE_KERNEL_NOISE));
>+	cpumask_copy(&watchdog_cpumask_boot, &watchdog_cpumask);
> 
> 	if (!watchdog_hardlockup_probe())
> 		watchdog_hardlockup_available = true;
>
>


--- Thanks!
"I'm not a very positive person" - Linus torvalds