executor: ignore workdir if already exists

executor/containerdexecutor/executor.go

@@ -99,9 +99,11 @@ func (w containerdExecutor) Exec(ctx context.Context, meta executor.Meta, root c
 			lm.Unmount()
 			return errors.Wrapf(err, "working dir %s points to invalid target", newp)
 		}
-		if err := idtools.MkdirAllAndChown(newp, 0755, identity); err != nil {
-			lm.Unmount()
-			return errors.Wrapf(err, "failed to create working directory %s", newp)
+		if _, err := os.Stat(newp); err != nil {
+			if err := idtools.MkdirAllAndChown(newp, 0755, identity); err != nil {
+				lm.Unmount()
+				return errors.Wrapf(err, "failed to create working directory %s", newp)
+			}
 		}
 
 		lm.Unmount()

executor/runcexecutor/executor.go

@@ -236,8 +236,10 @@ func (w *runcExecutor) Exec(ctx context.Context, meta executor.Meta, root cache.
 	if err != nil {
 		return errors.Wrapf(err, "working dir %s points to invalid target", newp)
 	}
-	if err := idtools.MkdirAllAndChown(newp, 0755, identity); err != nil {
-		return errors.Wrapf(err, "failed to create working directory %s", newp)
+	if _, err := os.Stat(newp); err != nil {
+		if err := idtools.MkdirAllAndChown(newp, 0755, identity); err != nil {
+			return errors.Wrapf(err, "failed to create working directory %s", newp)
+		}
 	}
 
 	if err := setOOMScoreAdj(spec); err != nil {

frontend/dockerfile/dockerfile_test.go

@@ -108,6 +108,7 @@ var fileOpTests = []integration.Test{
 	testTarContext,
 	testTarContextExternalDockerfile,
 	testWorkdirUser,
+	testWorkdirExists,
 }
 
 var securityTests = []integration.Test{}
@@ -805,6 +806,40 @@ RUN [ "$(stat -c "%U %G" /mydir)" == "user user" ]
 	require.NoError(t, err)
 }
 
+func testWorkdirExists(t *testing.T, sb integration.Sandbox) {
+	f := getFrontend(t, sb)
+	isFileOp := getFileOp(t, sb)
+
+	dockerfile := []byte(`
+FROM busybox
+RUN adduser -D user
+RUN mkdir /mydir && chown user:user /mydir
+WORKDIR /mydir
+RUN [ "$(stat -c "%U %G" /mydir)" == "user user" ]
+`)
+
+	dir, err := tmpdir(
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	c, err := client.New(context.TODO(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	_, err = f.Solve(context.TODO(), c, client.SolveOpt{
+		FrontendAttrs: map[string]string{
+			"build-arg:BUILDKIT_DISABLE_FILEOP": strconv.FormatBool(!isFileOp),
+		},
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+}
+
 func testCopyChownCreateDest(t *testing.T, sb integration.Sandbox) {
 	f := getFrontend(t, sb)
 	isFileOp := getFileOp(t, sb)