mm: userfaultfd: use swap() in double_pt_lock()

Use existing swap() function rather than duplicating its implementation.

./mm/userfaultfd.c:1006:13-14: WARNING opportunity for swap()

Link: https://lkml.kernel.org/r/20240531091643.67778-1-jiapeng.chong@linux.alibaba.comSigned-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=9266Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/userfaultfd.c

@@ -995,14 +995,8 @@ void double_pt_lock(spinlock_t *ptl1,
 	__acquires(ptl1)
 	__acquires(ptl2)
 {
-	spinlock_t *ptl_tmp;
-
-	if (ptl1 > ptl2) {
-		/* exchange ptl1 and ptl2 */
-		ptl_tmp = ptl1;
-		ptl1 = ptl2;
-		ptl2 = ptl_tmp;
-	}
+	if (ptl1 > ptl2)
+		swap(ptl1, ptl2);
 	/* lock in virtual address order to avoid lock inversion */
 	spin_lock(ptl1);
 	if (ptl1 != ptl2)