Mark some kernfs inode as Anonymous.

These inodes can never be part of a filesystem tree. They are nameless and
never have a parent.

This allows us to avoid taking a lock in kernfs.InotifyWithParent for such
anonymous inodes.

PiperOrigin-RevId: 538823227

pkg/sentry/fsimpl/cgroupfs/cgroupfs.go

@@ -496,11 +496,12 @@ func (*implStatFS) StatFS(context.Context, *vfs.Filesystem) (linux.Statfs, error
 //
 // +stateify savable
 type dir struct {
-	kernfs.InodeNoopRefCount
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
-	kernfs.InodeNotSymlink
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
+	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
 	kernfs.OrderedChildren
 	implStatFS

pkg/sentry/fsimpl/devpts/devpts.go

@@ -150,6 +150,7 @@ type rootInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary // This holds no meaning as this inode can't be Looked up and is always valid.
 	kernfs.InodeWatches

pkg/sentry/fsimpl/devpts/master.go

@@ -36,6 +36,7 @@ type masterInode struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches

pkg/sentry/fsimpl/devpts/replica.go

@@ -35,6 +35,7 @@ type replicaInode struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches

pkg/sentry/fsimpl/fuse/inode.go

@@ -45,6 +45,7 @@ type fileHandle struct {
 type inode struct {
 	inodeRefs
 	kernfs.InodeAlwaysValid
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
 	kernfs.OrderedChildren

pkg/sentry/fsimpl/host/host.go

@@ -94,10 +94,11 @@ func isEpollable(fd int) bool {
 //
 // +stateify savable
 type inode struct {
+	kernfs.CachedMappable
 	kernfs.InodeNoStatFS
+	kernfs.InodeAnonymous // inode is effectively anonymous because it represents a donated FD.
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
-	kernfs.CachedMappable
 	kernfs.InodeTemporary // This holds no meaning as this inode can't be Looked up and is always valid.
 	kernfs.InodeWatches
 

pkg/sentry/fsimpl/kernfs/dynamic_bytes_file.go

@@ -38,6 +38,7 @@ type DynamicBytesFile struct {
 	InodeAttrs
 	InodeNoStatFS
 	InodeNoopRefCount
+	InodeNotAnonymous
 	InodeNotDirectory
 	InodeNotSymlink
 	InodeWatches

pkg/sentry/fsimpl/kernfs/inode_impl_util.go

@@ -724,6 +724,7 @@ type StaticDirectory struct {
 	InodeAttrs
 	InodeDirectoryNoNewChildren
 	InodeNoStatFS
+	InodeNotAnonymous
 	InodeNotSymlink
 	InodeTemporary
 	InodeWatches
@@ -819,3 +820,23 @@ type InodeWatches struct {
 func (i *InodeWatches) Watches() *vfs.Watches {
 	return &i.watches
 }
+
+// InodeAnonymous partially implements Inode.
+//
+// +stateify savable
+type InodeAnonymous struct{}
+
+// Anonymous implements Inode.Anonymous
+func (*InodeAnonymous) Anonymous() bool {
+	return true
+}
+
+// InodeNotAnonymous partially implements Inode.
+//
+// +stateify savable
+type InodeNotAnonymous struct{}
+
+// Anonymous implements Inode.Anonymous
+func (*InodeNotAnonymous) Anonymous() bool {
+	return false
+}

pkg/sentry/fsimpl/kernfs/kernfs.go

@@ -514,12 +514,18 @@ func (d *Dentry) InotifyWithParent(ctx context.Context, events, cookie uint32, e
 		events |= linux.IN_ISDIR
 	}
 
-	d.fs.mu.RLock()
-	defer d.fs.mu.RUnlock()
-	// The ordering below is important, Linux always notifies the parent first.
-	if d.parent != nil {
-		d.parent.inode.Watches().Notify(ctx, d.name, events, cookie, et, d.isDeleted())
+	// Linux always notifies the parent first.
+
+	// Don't bother looking for a parent if the inode is anonymous. It
+	// won't have one.
+	if !d.inode.Anonymous() {
+		d.fs.mu.RLock()
+		if d.parent != nil {
+			d.parent.inode.Watches().Notify(ctx, d.name, events, cookie, et, d.isDeleted())
+		}
+		d.fs.mu.RUnlock()
 	}
+
 	d.inode.Watches().Notify(ctx, "", events, cookie, et, d.isDeleted())
 }
 
@@ -704,6 +710,10 @@ type Inode interface {
 
 	// Watches returns the set of inotify watches associated with this inode.
 	Watches() *vfs.Watches
+
+	// Anonymous indicates that the Inode is anonymous. It will never have
+	// a name or parent.
+	Anonymous() bool
 }
 
 type inodeRefs interface {

pkg/sentry/fsimpl/kernfs/kernfs_test.go

@@ -104,6 +104,7 @@ type readonlyDir struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeDirectoryNoNewChildren
 	kernfs.InodeNoStatFS
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
@@ -139,8 +140,9 @@ type dir struct {
 	dirRefs
 	attrs
 	kernfs.InodeAlwaysValid
-	kernfs.InodeNotSymlink
 	kernfs.InodeNoStatFS
+	kernfs.InodeNotAnonymous
+	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
 	kernfs.OrderedChildren

pkg/sentry/fsimpl/kernfs/symlink.go

@@ -29,6 +29,7 @@ import (
 type StaticSymlink struct {
 	InodeAttrs
 	InodeNoopRefCount
+	InodeNotAnonymous
 	InodeSymlink
 	InodeNoStatFS
 	InodeWatches

pkg/sentry/fsimpl/kernfs/synthetic_directory.go

@@ -32,6 +32,7 @@ type syntheticDirectory struct {
 	InodeAlwaysValid
 	InodeAttrs
 	InodeNoStatFS
+	InodeNotAnonymous
 	InodeNotSymlink
 	InodeWatches
 	OrderedChildren

pkg/sentry/fsimpl/mqfs/root.go

@@ -29,6 +29,7 @@ import (
 type rootInode struct {
 	rootInodeRefs
 	kernfs.InodeAlwaysValid
+	kernfs.InodeAnonymous
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
 	kernfs.InodeNotSymlink

pkg/sentry/fsimpl/pipefs/pipefs.go

@@ -89,6 +89,7 @@ func (fs *filesystem) MountOptions() string {
 //
 // +stateify savable
 type inode struct {
+	kernfs.InodeAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeNoopRefCount

pkg/sentry/fsimpl/proc/subtasks.go

@@ -35,6 +35,7 @@ type subtasksInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches

pkg/sentry/fsimpl/proc/task.go

@@ -35,6 +35,7 @@ type taskInode struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches

pkg/sentry/fsimpl/proc/task_fds.go

@@ -113,6 +113,7 @@ type fdDirInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches
@@ -198,6 +199,7 @@ type fdSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -257,6 +259,7 @@ type fdInfoDirInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary
 	kernfs.InodeWatches

pkg/sentry/fsimpl/proc/task_files.go

@@ -410,6 +410,7 @@ type memInode struct {
 	kernfs.InodeAttrs
 	kernfs.InodeNoStatFS
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
@@ -730,6 +731,7 @@ type statusInode struct {
 	kernfs.InodeAttrs
 	kernfs.InodeNoStatFS
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches
@@ -963,6 +965,7 @@ type exeSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -1035,6 +1038,7 @@ type cwdSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -1096,6 +1100,7 @@ type rootSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -1269,6 +1274,7 @@ type namespaceInode struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotDirectory
 	kernfs.InodeNotSymlink
 	kernfs.InodeWatches

pkg/sentry/fsimpl/proc/tasks.go

@@ -41,6 +41,7 @@ type tasksInode struct {
 	kernfs.InodeAlwaysValid
 	kernfs.InodeAttrs
 	kernfs.InodeDirectoryNoNewChildren
+	kernfs.InodeNotAnonymous
 	kernfs.InodeNotSymlink
 	kernfs.InodeTemporary // This holds no meaning as this inode can't be Looked up and is always valid.
 	kernfs.InodeWatches

pkg/sentry/fsimpl/proc/tasks_files.go

@@ -37,6 +37,7 @@ type selfSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches
 
@@ -79,6 +80,7 @@ type threadSelfSymlink struct {
 	implStatFS
 	kernfs.InodeAttrs
 	kernfs.InodeNoopRefCount
+	kernfs.InodeNotAnonymous
 	kernfs.InodeSymlink
 	kernfs.InodeWatches