3 files changed, 24 insertions, 21 deletions
diff --git a/pkg/sentry/fs/fs.go b/pkg/sentry/fs/fs.go
index b5c72990e..0ba4b7269 100644
--- a/pkg/sentry/fs/fs.go
+++ b/pkg/sentry/fs/fs.go
@@ -44,7 +44,7 @@
 //         DirentCache.mu
 //         Locks in InodeOperations implementations or overlayEntry
 //         Inode.Watches.mu (see `Inotify` for other lock ordering)
-//	   MountSource.mu
+//         MountSource.mu
 //
 // If multiple Dirent or MountSource locks must be taken, locks in the parent must be
 // taken before locks in their children.
@@ -60,10 +60,11 @@ import (
 )
 
 var (
-	// work is a sync.WaitGroup that can be used to queue asynchronous
-	// operations via Do. Callers can use Barrier to ensure no operations
-	// are outstanding.
-	work sync.WaitGroup
+	// workMu is used to synchronize pending asynchronous work. Async work
+	// runs with the lock held for reading. AsyncBarrier will take the lock
+	// for writing, thus ensuring that all Async work completes before
+	// AsyncBarrier returns.
+	workMu sync.RWMutex
 
 	// asyncError is used to store up to one asynchronous execution error.
 	asyncError = make(chan error, 1)
@@ -71,14 +72,17 @@ var (
 
 // AsyncBarrier waits for all outstanding asynchronous work to complete.
 func AsyncBarrier() {
-	work.Wait()
+	workMu.Lock()
+	workMu.Unlock()
 }
 
 // Async executes a function asynchronously.
+//
+// Async must not be called recursively.
 func Async(f func()) {
-	work.Add(1)
-	go func() { // S/R-SAFE: Barrier must be called.
-		defer work.Done() // Ensure Done in case of panic.
+	workMu.RLock()
+	go func() { // S/R-SAFE: AsyncBarrier must be called.
+		defer workMu.RUnlock() // Ensure RUnlock in case of panic.
 		f()
 	}()
 }
@@ -89,7 +93,7 @@ func Async(f func()) {
 func AsyncErrorBarrier() error {
 	wait := make(chan struct{}, 1)
 	go func() { // S/R-SAFE: Does not touch persistent state.
-		work.Wait()
+		AsyncBarrier()
 		wait <- struct{}{}
 	}()
 	select {
diff --git a/pkg/sentry/fs/gofer/inode.go b/pkg/sentry/fs/gofer/inode.go
index 5811b8b12..7c6e5b025 100644
--- a/pkg/sentry/fs/gofer/inode.go
+++ b/pkg/sentry/fs/gofer/inode.go
@@ -333,8 +333,14 @@ func (i *inodeOperations) session() *session {
 
 // Release implements fs.InodeOperations.Release.
 func (i *inodeOperations) Release(ctx context.Context) {
-	i.fileState.Release(ctx)
 	i.cachingInodeOps.Release()
+
+	// Releasing the fileState may make RPCs to the gofer. There is
+	// no need to wait for those to return, so we can do this
+	// asynchronously.
+	fs.Async(func() {
+		i.fileState.Release(ctx)
+	})
 }
 
 // Mappable implements fs.InodeOperations.Mappable.
diff --git a/pkg/sentry/fs/inode.go b/pkg/sentry/fs/inode.go
index 38b140bd2..fa3beb111 100644
--- a/pkg/sentry/fs/inode.go
+++ b/pkg/sentry/fs/inode.go
@@ -110,20 +110,13 @@ func (i *Inode) destroy() {
 	// wouldn't be in the destructor.
 	i.Watches.targetDestroyed()
 
-	// Overlay resources should be released synchronously, since they may
-	// trigger more Inode.destroy calls which must themselves be handled
-	// synchronously, like the WriteOut call above.
 	if i.overlay != nil {
 		i.overlay.release()
-		i.MountSource.DecRef()
-		return
+	} else {
+		i.InodeOperations.Release(ctx)
 	}
 
-	// Regular (non-overlay) resources may be released asynchronously.
-	Async(func() {
-		i.InodeOperations.Release(ctx)
-		i.MountSource.DecRef()
-	})
+	i.MountSource.DecRef()
 }
 
 // Mappable calls i.InodeOperations.Mappable.