maple_tree: clean up mas_wr_append()

Avoid setting the variables until necessary, and actually use the
variables where applicable.  Introducing a variable for the slots array
avoids spanning multiple lines.

Add the missing argument to the documentation.

Use the node type when setting the metadata instead of blindly assuming
the type.

Finally, add a trace point to the function for successful store.

Link: https://lkml.kernel.org/r/20230819004356.1454718-3-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -4106,6 +4106,7 @@ static inline unsigned char mas_wr_new_end(struct ma_wr_state *wr_mas)
 /*
  * mas_wr_append: Attempt to append
  * @wr_mas: the maple write state
+ * @new_end: The end of the node after the modification
  *
  * This is currently unsafe in rcu mode since the end of the node may be cached
  * by readers while the node contents may be updated which could result in
@@ -4114,49 +4115,54 @@ static inline unsigned char mas_wr_new_end(struct ma_wr_state *wr_mas)
  * Return: True if appended, false otherwise
  */
 static inline bool mas_wr_append(struct ma_wr_state *wr_mas,
-				 unsigned char new_end)
+		unsigned char new_end)
 {
-	unsigned char end = wr_mas->node_end;
-	struct ma_state *mas = wr_mas->mas;
-	unsigned char node_pivots = mt_pivots[wr_mas->type];
+	struct ma_state *mas;
+	void __rcu **slots;
+	unsigned char end;
 
+	mas = wr_mas->mas;
 	if (mt_in_rcu(mas->tree))
 		return false;
 
 	if (mas->offset != wr_mas->node_end)
 		return false;
 
-	if (new_end < node_pivots) {
+	end = wr_mas->node_end;
+	if (mas->offset != end)
+		return false;
+
+	if (new_end < mt_pivots[wr_mas->type]) {
 		wr_mas->pivots[new_end] = wr_mas->pivots[end];
-		ma_set_meta(wr_mas->node, maple_leaf_64, 0, new_end);
+		ma_set_meta(wr_mas->node, wr_mas->type, 0, new_end);
 	}
 
-	if (new_end == wr_mas->node_end + 1) {
+	slots = wr_mas->slots;
+	if (new_end == end + 1) {
 		if (mas->last == wr_mas->r_max) {
 			/* Append to end of range */
-			rcu_assign_pointer(wr_mas->slots[new_end],
-					   wr_mas->entry);
+			rcu_assign_pointer(slots[new_end], wr_mas->entry);
 			wr_mas->pivots[end] = mas->index - 1;
 			mas->offset = new_end;
 		} else {
 			/* Append to start of range */
-			rcu_assign_pointer(wr_mas->slots[new_end],
-					   wr_mas->content);
+			rcu_assign_pointer(slots[new_end], wr_mas->content);
 			wr_mas->pivots[end] = mas->last;
-			rcu_assign_pointer(wr_mas->slots[end], wr_mas->entry);
+			rcu_assign_pointer(slots[end], wr_mas->entry);
 		}
 	} else {
 		/* Append to the range without touching any boundaries. */
-		rcu_assign_pointer(wr_mas->slots[new_end], wr_mas->content);
+		rcu_assign_pointer(slots[new_end], wr_mas->content);
 		wr_mas->pivots[end + 1] = mas->last;
-		rcu_assign_pointer(wr_mas->slots[end + 1], wr_mas->entry);
+		rcu_assign_pointer(slots[end + 1], wr_mas->entry);
 		wr_mas->pivots[end] = mas->index - 1;
 		mas->offset = end + 1;
 	}
 
 	if (!wr_mas->content || !wr_mas->entry)
 		mas_update_gap(mas);
 
+	trace_ma_write(__func__, mas, new_end, wr_mas->entry);
 	return  true;
 }