4 files changed, 11 insertions, 28 deletions
diff --git a/pkg/sentry/fsimpl/mqfs/mqfs.go b/pkg/sentry/fsimpl/mqfs/mqfs.go
index c2b53c9d0..9b3704217 100644
--- a/pkg/sentry/fsimpl/mqfs/mqfs.go
+++ b/pkg/sentry/fsimpl/mqfs/mqfs.go
@@ -75,6 +75,7 @@ func (ft FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.VirtualF
 	impl.fs.MaxCachedDentries = maxCachedDentries
 
 	impl.fs.VFSFilesystem().IncRef()
+	impl.root.IncRef()
 	return impl.fs.VFSFilesystem(), impl.root.VFSDentry(), nil
 }
 
@@ -100,10 +101,6 @@ func maxCachedDentries(ctx context.Context, mopts map[string]string) (_ uint64,
 type filesystem struct {
 	kernfs.Filesystem
 	devMinor uint32
-
-	// root is the filesystem's root dentry. Since we take a reference on it in
-	// GetFilesystem, we should release it when the fs is released.
-	root *kernfs.Dentry
 }
 
 // Release implements vfs.FilesystemImpl.Release.
diff --git a/pkg/sentry/fsimpl/mqfs/registry.go b/pkg/sentry/fsimpl/mqfs/registry.go
index c8fbe4d33..e470ffadc 100644
--- a/pkg/sentry/fsimpl/mqfs/registry.go
+++ b/pkg/sentry/fsimpl/mqfs/registry.go
@@ -57,16 +57,19 @@ func NewRegistryImpl(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *
 		return nil, err
 	}
 
-	var dentry kernfs.Dentry
 	fs := &filesystem{
 		devMinor: devMinor,
-		root:     &dentry,
 	}
 	fs.VFSFilesystem().Init(vfsObj, &FilesystemType{}, fs)
 	vfsfs := fs.VFSFilesystem()
+	// NewDisconnectedMount will obtain a ref on dentry and vfsfs which is
+	// transferred to mount. vfsfs was initiated with 1 ref already. So get rid
+	// of the extra ref.
+	defer vfsfs.DecRef(ctx)
 
+	// dentry is initialized with 1 ref which is transferred to fs.
+	var dentry kernfs.Dentry
 	dentry.InitRoot(&fs.Filesystem, fs.newRootInode(ctx, creds))
-	defer vfsfs.DecRef(ctx) // NewDisconnectedMount will obtain a ref on success.
 
 	mount, err := vfsObj.NewDisconnectedMount(vfsfs, dentry.VFSDentry(), &vfs.MountOptions{})
 	if err != nil {
@@ -82,7 +85,7 @@ func NewRegistryImpl(ctx context.Context, vfsObj *vfs.VirtualFilesystem, creds *
 
 // Get implements mq.RegistryImpl.Get.
 func (r *RegistryImpl) Get(ctx context.Context, name string, access mq.AccessType, block bool, flags uint32) (*vfs.FileDescription, bool, error) {
-	inode, err := r.lookup(ctx, name)
+	inode, err := r.root.Inode().(*rootInode).Lookup(ctx, name)
 	if err != nil {
 		return nil, false, nil
 	}
@@ -120,7 +123,7 @@ func (r *RegistryImpl) Unlink(ctx context.Context, name string) error {
 	}
 
 	root := r.root.Inode().(*rootInode)
-	inode, err := r.lookup(ctx, name)
+	inode, err := root.Lookup(ctx, name)
 	if err != nil {
 		return err
 	}
@@ -133,16 +136,6 @@ func (r *RegistryImpl) Destroy(ctx context.Context) {
 	r.mount.DecRef(ctx)
 }
 
-// lookup retreives a kernfs.Inode using a name.
-func (r *RegistryImpl) lookup(ctx context.Context, name string) (kernfs.Inode, error) {
-	inode := r.root.Inode().(*rootInode)
-	lookup, err := inode.Lookup(ctx, name)
-	if err != nil {
-		return nil, err
-	}
-	return lookup, nil
-}
-
 // newFD returns a new file description created using the given queue and inode.
 func (r *RegistryImpl) newFD(q *mq.Queue, inode *queueInode, access mq.AccessType, block bool, flags uint32) (*vfs.FileDescription, error) {
 	view, err := mq.NewView(q, access, block)
diff --git a/pkg/sentry/fsimpl/mqfs/root.go b/pkg/sentry/fsimpl/mqfs/root.go
index 37b5749fb..922e669e2 100644
--- a/pkg/sentry/fsimpl/mqfs/root.go
+++ b/pkg/sentry/fsimpl/mqfs/root.go
@@ -34,7 +34,6 @@ type rootInode struct {
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.OrderedChildren
-	implStatFS
 
 	locks vfs.FileLocks
 }
@@ -77,13 +76,7 @@ func (*rootInode) SetStat(context.Context, *vfs.Filesystem, *auth.Credentials, v
 	return linuxerr.EPERM
 }
 
-// implStatFS provides an implementation of kernfs.Inode.StatFS for message
-// queues to be embedded in inodes.
-//
-// +stateify savable
-type implStatFS struct{}
-
 // StatFS implements kernfs.Inode.StatFS.
-func (*implStatFS) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error) {
+func (*rootInode) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error) {
 	return vfs.GenericStatFS(linux.MQUEUE_MAGIC), nil
 }
diff --git a/pkg/sentry/vfs/filesystem_type.go b/pkg/sentry/vfs/filesystem_type.go
index 9d54cc4ed..70d6eb85e 100644
--- a/pkg/sentry/vfs/filesystem_type.go
+++ b/pkg/sentry/vfs/filesystem_type.go
@@ -28,7 +28,7 @@ import (
 type FilesystemType interface {
 	// GetFilesystem returns a Filesystem configured by the given options,
 	// along with its mount root. A reference is taken on the returned
-	// Filesystem and Dentry.
+	// Filesystem and Dentry whose ownership is transferred to the caller.
 	GetFilesystem(ctx context.Context, vfsObj *VirtualFilesystem, creds *auth.Credentials, source string, opts GetFilesystemOptions) (*Filesystem, *Dentry, error)
 
 	// Name returns the name of this FilesystemType.