Ticket #60855: 60855.patch

src/wp-includes/functions.php

@@ -2097 +2097 @@
                 return true;
         }
 
+        /*
+         * If we get here, mkdir() failed.
+         *
+         * Maybe another process was trying to create the directory at the same time
+         * (and succeeded)?
+         *
+         * Check if the target exists (again).
+         */
+        if ( file_exists( $target ) ) {
+                return @is_dir( $target );
+        }
+
         return false;
 }