workqueue: skip the node_nr_active update for non-unbound workqueuesgrafted

apply_wqattrs_commit() updates node_nr_active->max unconditionally.
wq->node_nr_active[] is only allocated for unbound workqueues, so guard
the call before per-cpu workqueues start using this path.

No functional change: only unbound workqueues reach apply_wqattrs_*()
today.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 49 insertions, 0 deletions

diff --git a/lib/union_find.c b/lib/union_find.c
new file mode 100644
index 000000000..413b0f8ad
--- /dev/null
+++ b/lib/union_find.c
@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/union_find.h>
+
+/**
+ * uf_find - Find the root of a node and perform path compression
+ * @node: the node to find the root of
+ *
+ * This function returns the root of the node by following the parent
+ * pointers. It also performs path compression, making the tree shallower.
+ *
+ * Returns the root node of the set containing node.
+ */
+struct uf_node *uf_find(struct uf_node *node)
+{
+	struct uf_node *parent;
+
+	while (node->parent != node) {
+		parent = node->parent;
+		node->parent = parent->parent;
+		node = parent;
+	}
+	return node;
+}
+
+/**
+ * uf_union - Merge two sets, using union by rank
+ * @node1: the first node
+ * @node2: the second node
+ *
+ * This function merges the sets containing node1 and node2, by comparing
+ * the ranks to keep the tree balanced.
+ */
+void uf_union(struct uf_node *node1, struct uf_node *node2)
+{
+	struct uf_node *root1 = uf_find(node1);
+	struct uf_node *root2 = uf_find(node2);
+
+	if (root1 == root2)
+		return;
+
+	if (root1->rank < root2->rank) {
+		root1->parent = root2;
+	} else if (root1->rank > root2->rank) {
+		root2->parent = root1;
+	} else {
+		root2->parent = root1;
+		root1->rank++;
+	}
+}