[release-1.51] overlay: create the merged path only if it does not exist

follow-up for ccb70a7

more information here: containers#1827 (comment)

Addresses: https://issues.redhat.com/browse/ACCELFIX-244

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>
Signed-off-by: tomsweeneyredhat <tsweeney@redhat.com>

drivers/overlay/overlay.go

@@ -1680,9 +1680,11 @@ func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountO
 	}
 
 	mergedDir := path.Join(workDirBase, "merged")
-	// Create the driver merged dir
-	if err := idtools.MkdirAs(mergedDir, 0o700, rootUID, rootGID); err != nil && !os.IsExist(err) {
-		return "", err
+	// Attempt to create the merged dir only if it doesn't exist.
+	if _, err := os.Stat(mergedDir); err != nil && os.IsNotExist(err) {
+		if err := idtools.MkdirAs(mergedDir, 0o700, rootUID, rootGID); err != nil && !os.IsExist(err) {
+			return "", err
+		}
 	}
 	if count := d.ctr.Increment(mergedDir); count > 1 {
 		return mergedDir, nil

tests/overlay-recreate.bats

@@ -18,7 +18,8 @@ load helpers
 	storage unmount "$lowerlayer"
 	storage mount "$midlayer"
 	storage unmount "$midlayer"
-	storage mount "$upperlayer"
+	run storage --debug=false mount "$upperlayer"
+	merged_dir="$output"
 	storage unmount "$upperlayer"
 	# okay, but how about this?
 	rm -v ${TESTDIR}/root/overlay/*/link
@@ -27,6 +28,8 @@ load helpers
 	storage unmount "$lowerlayer"
 	storage mount "$midlayer"
 	storage unmount "$midlayer"
+	# check it works if we delete the merged directory.
+	rmdir "$merged_dir"
 	storage mount "$upperlayer"
 	storage unmount "$upperlayer"
 	# okay, not bad, kid.