[PATCH -next RFC 04/11] cpuset: Refactor exclusive CPU mask computation logic

[Chen Ridong <chenridong@huaweicloud.com>]

From: Chen Ridong <chenridong@huawei.com>

The current compute_effective_exclusive_cpumask function handles multiple
scenarios with different input parameters, making the code difficult to
follow. This patch refactors it into two separate functions:
compute_excpus and compute_trialcs_excpus.

The compute_excpus function calculates the exclusive CPU mask for a given
input and excludes exclusive CPUs from sibling cpusets when cs's
exclusive_cpus is not explicitly set.

The compute_trialcs_excpus function specifically handles exclusive CPU
computation for trial cpusets used during CPU mask configuration updates,
and always excludes exclusive CPUs from sibling cpusets.

This refactoring significantly improves code readability and clarity,
making it explicit which function to call for each use case and what
parameters should be provided.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
---
 kernel/cgroup/cpuset.c | 103 ++++++++++++++++++++++++++---------------
 1 file changed, 65 insertions(+), 38 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 595a8346f823..fc367ae741cf 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1402,38 +1402,25 @@ bool cpuset_cpu_is_isolated(int cpu)
 }
 EXPORT_SYMBOL_GPL(cpuset_cpu_is_isolated);
 
-/*
- * compute_effective_exclusive_cpumask - compute effective exclusive CPUs
- * @cs: cpuset
- * @xcpus: effective exclusive CPUs value to be set
- * @real_cs: the real cpuset (can be NULL)
- * Return: 0 if there is no sibling conflict, > 0 otherwise
+/**
+ * rm_siblings_excl_cpus - Remove exclusive CPUs that are used by sibling cpusets
+ * @parent: Parent cpuset containing all siblings
+ * @cs: Current cpuset (will be skipped)
+ * @excpus:  exclusive effective CPU mask to modify
  *
- * If exclusive_cpus isn't explicitly set or a real_cs is provided, we have to
- * scan the sibling cpusets and exclude their exclusive_cpus or effective_xcpus
- * as well. The provision of real_cs means that a cpumask is being changed and
- * the given cs is a trial one.
+ * This function ensures the given @excpus mask doesn't include any CPUs that
+ * are exclusively allocated to sibling cpusets. It walks through all siblings
+ * of @cs under @parent and removes their exclusive CPUs from @excpus.
  */
-static int compute_effective_exclusive_cpumask(struct cpuset *cs,
-					       struct cpumask *xcpus,
-					       struct cpuset *real_cs)
+static int rm_siblings_excl_cpus(struct cpuset *parent, struct cpuset *cs,
+					struct cpumask *excpus)
 {
 	struct cgroup_subsys_state *css;
-	struct cpuset *parent = parent_cs(cs);
 	struct cpuset *sibling;
 	int retval = 0;
 
-	if (!xcpus)
-		xcpus = cs->effective_xcpus;
-
-	cpumask_and(xcpus, user_xcpus(cs), parent->effective_xcpus);
-
-	if (!real_cs) {
-		if (!cpumask_empty(cs->exclusive_cpus))
-			return 0;
-	} else {
-		cs = real_cs;
-	}
+	if (cpumask_empty(excpus))
+		return retval;
 
 	/*
 	 * Exclude exclusive CPUs from siblings
@@ -1443,20 +1430,60 @@ static int compute_effective_exclusive_cpumask(struct cpuset *cs,
 		if (sibling == cs)
 			continue;
 
-		if (cpumask_intersects(xcpus, sibling->exclusive_cpus)) {
-			cpumask_andnot(xcpus, xcpus, sibling->exclusive_cpus);
+		if (cpumask_intersects(excpus, sibling->exclusive_cpus)) {
+			cpumask_andnot(excpus, excpus, sibling->exclusive_cpus);
 			retval++;
 			continue;
 		}
-		if (cpumask_intersects(xcpus, sibling->effective_xcpus)) {
-			cpumask_andnot(xcpus, xcpus, sibling->effective_xcpus);
+		if (cpumask_intersects(excpus, sibling->effective_xcpus)) {
+			cpumask_andnot(excpus, excpus, sibling->effective_xcpus);
 			retval++;
 		}
 	}
 	rcu_read_unlock();
+
 	return retval;
 }
 
+/*
+ * compute_excpus - compute effective exclusive CPUs
+ * @cs: cpuset
+ * @xcpus: effective exclusive CPUs value to be set
+ * Return: 0 if there is no sibling conflict, > 0 otherwise
+ *
+ * If exclusive_cpus isn't explicitly set , we have to scan the sibling cpusets
+ * and exclude their exclusive_cpus or effective_xcpus as well.
+ */
+static int compute_excpus(struct cpuset *cs, struct cpumask *excpus)
+{
+	struct cpuset *parent = parent_cs(cs);
+
+	cpumask_and(excpus, user_xcpus(cs), parent->effective_xcpus);
+
+	if (!cpumask_empty(cs->exclusive_cpus))
+		return 0;
+
+	return rm_siblings_excl_cpus(parent, cs, excpus);
+}
+
+/*
+ * compute_trialcs_excpus - Compute effective exclusive CPUs for a trial cpuset
+ * @trialcs: The trial cpuset containing the proposed new configuration
+ * @cs: The original cpuset that the trial configuration is based on
+ * Return: 0 if successful with no sibling conflict, >0 if a conflict is found
+ *
+ * Computes the effective_xcpus for a trial configuration. @cs is provided to represent
+ * the real cs.
+ */
+static int compute_trialcs_excpus(struct cpuset *trialcs, struct cpuset *cs)
+{
+	struct cpuset *parent = parent_cs(trialcs);
+	struct cpumask *excpus = trialcs->effective_xcpus;
+
+	cpumask_and(excpus, user_xcpus(trialcs), parent->effective_xcpus);
+	return rm_siblings_excl_cpus(parent, cs, excpus);
+}
+
 static inline bool is_remote_partition(struct cpuset *cs)
 {
 	return !list_empty(&cs->remote_sibling);
@@ -1498,7 +1525,7 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
 	 * Note that creating a remote partition with any local partition root
 	 * above it or remote partition root underneath it is not allowed.
 	 */
-	compute_effective_exclusive_cpumask(cs, tmp->new_cpus, NULL);
+	compute_excpus(cs, tmp->new_cpus);
 	WARN_ON_ONCE(cpumask_intersects(tmp->new_cpus, subpartitions_cpus));
 	if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) ||
 	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus))
@@ -1547,7 +1574,7 @@ static void remote_partition_disable(struct cpuset *cs, struct tmpmasks *tmp)
 		cs->partition_root_state = PRS_MEMBER;
 
 	/* effective_xcpus may need to be changed */
-	compute_effective_exclusive_cpumask(cs, NULL, NULL);
+	compute_excpus(cs, cs->effective_xcpus);
 	reset_partition_data(cs);
 	spin_unlock_irq(&callback_lock);
 	update_unbound_workqueue_cpumask(isolcpus_updated);
@@ -1748,12 +1775,12 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
 
 	if ((cmd == partcmd_enable) || (cmd == partcmd_enablei)) {
 		/*
-		 * Need to call compute_effective_exclusive_cpumask() in case
+		 * Need to call compute_excpus() in case
 		 * exclusive_cpus not set. Sibling conflict should only happen
 		 * if exclusive_cpus isn't set.
 		 */
 		xcpus = tmp->delmask;
-		if (compute_effective_exclusive_cpumask(cs, xcpus, NULL))
+		if (compute_excpus(cs, xcpus))
 			WARN_ON_ONCE(!cpumask_empty(cs->exclusive_cpus));
 
 		/*
@@ -2035,7 +2062,7 @@ static void compute_partition_effective_cpumask(struct cpuset *cs,
 	 *  2) All the effective_cpus will be used up and cp
 	 *     has tasks
 	 */
-	compute_effective_exclusive_cpumask(cs, new_ecpus, NULL);
+	compute_excpus(cs, new_ecpus);
 	cpumask_and(new_ecpus, new_ecpus, cpu_active_mask);
 
 	rcu_read_lock();
@@ -2114,7 +2141,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 		 * its value is being processed.
 		 */
 		if (remote && (cp != cs)) {
-			compute_effective_exclusive_cpumask(cp, tmp->new_cpus, NULL);
+			compute_excpus(cp, tmp->new_cpus);
 			if (cpumask_equal(cp->effective_xcpus, tmp->new_cpus)) {
 				pos_css = css_rightmost_descendant(pos_css);
 				continue;
@@ -2216,7 +2243,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 		cpumask_copy(cp->effective_cpus, tmp->new_cpus);
 		cp->partition_root_state = new_prs;
 		if (!cpumask_empty(cp->exclusive_cpus) && (cp != cs))
-			compute_effective_exclusive_cpumask(cp, NULL, NULL);
+			compute_excpus(cp, cp->effective_xcpus);
 
 		/*
 		 * Make sure effective_xcpus is properly set for a valid
@@ -2365,7 +2392,7 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 		 * for checking validity of the partition root.
 		 */
 		if (!cpumask_empty(trialcs->exclusive_cpus) || is_partition_valid(cs))
-			compute_effective_exclusive_cpumask(trialcs, NULL, cs);
+			compute_trialcs_excpus(trialcs, cs);
 	}
 
 	/* Nothing to do if the cpus didn't change */
@@ -2501,7 +2528,7 @@ static int update_exclusive_cpumask(struct cpuset *cs, struct cpuset *trialcs,
 		 * Reject the change if there is exclusive CPUs conflict with
 		 * the siblings.
 		 */
-		if (compute_effective_exclusive_cpumask(trialcs, NULL, cs))
+		if (compute_trialcs_excpus(trialcs, cs))
 			return -EINVAL;
 	}
 
-- 
2.34.1