Re: [PATCH linux-next v2] sched/core: Add WARN() to check overflow in migrate_disable()

[Peter Zijlstra]

On Wed, Jul 03, 2024 at 08:53:25PM +0800, xu.xin16@xxxxxxxxxx wrote:

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 8cc4975d6b2b..327010af6ce9 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2259,6 +2259,7 @@ void migrate_disable(void)
>  	struct task_struct *p = current;
> 
>  	if (p->migration_disabled) {
> +		WARN(p->migration_disabled == USHRT_MAX, "migration_disabled has encountered an overflow.");
>  		p->migration_disabled++;
>  		return;
>  	}

How about we do something like this?

---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7a5ea8fc8abb..06a559532ed6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2237,6 +2237,12 @@ void migrate_disable(void)
 
 	if (p->migration_disabled) {
 		p->migration_disabled++;
+#ifdef CONFIG_DEBUG_PREEMPT
+		/*
+		 * Warn about overflow half-way through the range.
+		 */
+		WARN_ON_ONCE((s16)p->migration_disabled < 0);
+#endif
 		return;
 	}
 
@@ -2254,14 +2260,20 @@ void migrate_enable(void)
 		.flags     = SCA_MIGRATE_ENABLE,
 	};
 
+#ifdef CONFIG_DEBUG_PREEMPT
+	/*
+	 * Check both overflow from migrate_disable() and superfluous
+	 * migrate_enable().
+	 */
+	if (WARN_ON_ONCE((s16)p->migration_disabled <= 0))
+		return;
+#endif
+
 	if (p->migration_disabled > 1) {
 		p->migration_disabled--;
 		return;
 	}
 
-	if (WARN_ON_ONCE(!p->migration_disabled))
-		return;
-
 	/*
 	 * Ensure stop_task runs either before or after this, and that
 	 * __set_cpus_allowed_ptr(SCA_MIGRATE_ENABLE) doesn't schedule().