Use one mutex for both Registry and RegistryImpl.

Updates #136

pkg/sentry/fsimpl/mqfs/BUILD

@@ -35,7 +35,6 @@ go_library(
         "//pkg/sentry/kernel/ipc",
         "//pkg/sentry/kernel/mq",
         "//pkg/sentry/vfs",
-        "//pkg/sync",
         "//pkg/usermem",
         "//pkg/waiter",
     ],

pkg/sentry/fsimpl/mqfs/registry.go

@@ -23,18 +23,17 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/mq"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
-	"gvisor.dev/gvisor/pkg/sync"
 )
 
 // RegistryImpl implements mq.RegistryImpl. It implements the interface using
 // the message queue filesystem, and is provided to mq.Registry at
 // initialization.
 //
+// RegistryImpl is not thread-safe, so it is the responsibility of the user
+// (the containing mq.Registry) to protect using a lock.
+//
 // +stateify savable
 type RegistryImpl struct {
-	// mu protects all fields below.
-	mu sync.Mutex
-
 	// root is the root dentry of the mq filesystem. Its main usage is to
 	// retreive the root inode, which we use to add, remove, and lookup message
 	// queues.
@@ -82,9 +81,6 @@ 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) {
-	r.mu.Lock()
-	defer r.mu.Unlock()
-
 	inode, err := r.lookup(ctx, name)
 	if err != nil {
 		return nil, false, nil
@@ -106,9 +102,6 @@ func (r *RegistryImpl) Get(ctx context.Context, name string, access mq.AccessTyp
 
 // New implements mq.RegistryImpl.New.
 func (r *RegistryImpl) New(ctx context.Context, name string, q *mq.Queue, access mq.AccessType, block bool, perm linux.FileMode, flags uint32) (*vfs.FileDescription, error) {
-	r.mu.Lock()
-	defer r.mu.Unlock()
-
 	root := r.root.Inode().(*rootInode)
 	qInode := r.fs.newQueueInode(ctx, auth.CredentialsFromContext(ctx), q, perm).(*queueInode)
 	err := root.Insert(name, qInode)
@@ -120,9 +113,6 @@ func (r *RegistryImpl) New(ctx context.Context, name string, q *mq.Queue, access
 
 // Unlink implements mq.RegistryImpl.Unlink.
 func (r *RegistryImpl) Unlink(ctx context.Context, name string) error {
-	r.mu.Lock()
-	defer r.mu.Unlock()
-
 	creds := auth.CredentialsFromContext(ctx)
 	if err := r.root.Inode().CheckPermissions(ctx, creds, vfs.MayWrite|vfs.MayExec); err != nil {
 		return err
@@ -142,8 +132,6 @@ func (r *RegistryImpl) Destroy(ctx context.Context) {
 }
 
 // lookup retreives a kernfs.Inode using a name.
-//
-// Precondition: r.mu must be held.
 func (r *RegistryImpl) lookup(ctx context.Context, name string) (kernfs.Inode, error) {
 	inode := r.root.Inode().(*rootInode)
 	lookup, err := inode.Lookup(ctx, name)