From 085a907565921e84f59dfeb51da49af2d7c36c40 Mon Sep 17 00:00:00 2001
From: Michael Pratt <mpratt@google.com>
Date: Thu, 27 Jun 2019 14:22:40 -0700
Subject: Cache directory entries in the overlay

Currently, the overlay dirCache is only used for a single logical use of
getdents. i.e., it is discard when the FD is closed or seeked back to
the beginning.

But the initial work of getting the directory contents can be quite
expensive (particularly sorting large directories), so we should keep it
as long as possible.

This is very similar to the readdirCache in fs/gofer.

Since the upper filesystem does not have to allow caching readdir
entries, the new CacheReaddir MountSourceOperations method controls this
behavior.

This caching should be trivially movable to all Inodes if desired,
though that adds an additional copy step for non-overlay Inodes.
(Overlay Inodes already do the extra copy).

PiperOrigin-RevId: 255477592
---
 pkg/sentry/fs/BUILD              |  1 +
 pkg/sentry/fs/dirent.go          |  4 +-
 pkg/sentry/fs/file_overlay.go    | 85 ++++++++++++++++++++++------------------
 pkg/sentry/fs/fsutil/file.go     |  2 +-
 pkg/sentry/fs/gofer/file.go      |  2 +-
 pkg/sentry/fs/gofer/session.go   |  9 ++++-
 pkg/sentry/fs/host/file.go       |  2 +-
 pkg/sentry/fs/host/inode_test.go |  4 +-
 pkg/sentry/fs/inode_overlay.go   | 38 ++++++++++++++++--
 pkg/sentry/fs/mock.go            |  6 +++
 pkg/sentry/fs/mount.go           | 42 ++++++++++++++------
 pkg/sentry/fs/mount_overlay.go   | 11 ++++++
 pkg/sentry/fs/overlay.go         | 18 +++++++++
 pkg/sentry/fs/ramfs/dir.go       |  2 +-
 pkg/sentry/fs/tty/dir.go         |  2 +-
 pkg/sentry/fs/tty/fs.go          |  7 ++++
 16 files changed, 169 insertions(+), 66 deletions(-)

(limited to 'pkg')

diff --git a/pkg/sentry/fs/BUILD b/pkg/sentry/fs/BUILD
index e5b9b8bc2..d7259b47b 100644
--- a/pkg/sentry/fs/BUILD
+++ b/pkg/sentry/fs/BUILD
@@ -69,6 +69,7 @@ go_library(
         "//pkg/state",
         "//pkg/syserror",
         "//pkg/waiter",
+        "//third_party/gvsync",
     ],
 )
 
diff --git a/pkg/sentry/fs/dirent.go b/pkg/sentry/fs/dirent.go
index 3cba259d9..28651e58b 100644
--- a/pkg/sentry/fs/dirent.go
+++ b/pkg/sentry/fs/dirent.go
@@ -918,7 +918,7 @@ type DirIterator interface {
 	// calls, and must start with the given offset.
 	//
 	// The caller must ensure that this operation is permitted.
-	IterateDir(ctx context.Context, dirCtx *DirCtx, offset int) (int, error)
+	IterateDir(ctx context.Context, d *Dirent, dirCtx *DirCtx, offset int) (int, error)
 }
 
 // DirentReaddir serializes the directory entries of d including "." and "..".
@@ -988,7 +988,7 @@ func direntReaddir(ctx context.Context, d *Dirent, it DirIterator, root *Dirent,
 	// it.IterateDir should be passed an offset that does not include the
 	// initial dot elements.  We will add them back later.
 	offset -= 2
-	newOffset, err := it.IterateDir(ctx, dirCtx, int(offset))
+	newOffset, err := it.IterateDir(ctx, d, dirCtx, int(offset))
 	if int64(newOffset) < offset {
 		panic(fmt.Sprintf("node.Readdir returned offset %v less than input offset %v", newOffset, offset))
 	}
diff --git a/pkg/sentry/fs/file_overlay.go b/pkg/sentry/fs/file_overlay.go
index 5fb5fbe97..29e5618f4 100644
--- a/pkg/sentry/fs/file_overlay.go
+++ b/pkg/sentry/fs/file_overlay.go
@@ -85,12 +85,6 @@ type overlayFileOperations struct {
 	// protected by File.mu of the owning file, which is held during
 	// Readdir and Seek calls.
 	dirCursor string
-
-	// dirCacheMu protects dirCache.
-	dirCacheMu sync.RWMutex `state:"nosave"`
-
-	// dirCache is cache of DentAttrs from upper and lower Inodes.
-	dirCache *SortedDentryMap
 }
 
 // Release implements FileOperations.Release.
@@ -171,53 +165,68 @@ func (f *overlayFileOperations) Readdir(ctx context.Context, file *File, seriali
 	if root != nil {
 		defer root.DecRef()
 	}
+
 	dirCtx := &DirCtx{
 		Serializer: serializer,
 		DirCursor:  &f.dirCursor,
 	}
+	return DirentReaddir(ctx, file.Dirent, f, root, dirCtx, file.Offset())
+}
 
-	// If the directory dirent is frozen, then DirentReaddir will calculate
-	// the children based off the frozen dirent tree. There is no need to
-	// call readdir on the upper/lower layers.
-	if file.Dirent.frozen {
-		return DirentReaddir(ctx, file.Dirent, f, root, dirCtx, file.Offset())
+// IterateDir implements DirIterator.IterateDir.
+func (f *overlayFileOperations) IterateDir(ctx context.Context, d *Dirent, dirCtx *DirCtx, offset int) (int, error) {
+	o := d.Inode.overlay
+
+	if !d.Inode.MountSource.CacheReaddir() {
+		// Can't use the dirCache. Simply read the entries.
+		entries, err := readdirEntries(ctx, o)
+		if err != nil {
+			return offset, err
+		}
+		n, err := GenericReaddir(dirCtx, entries)
+		return offset + n, err
 	}
 
-	// Otherwise proceed with usual overlay readdir.
-	o := file.Dirent.Inode.overlay
+	// Otherwise, use or create cached entries.
+
+	o.dirCacheMu.RLock()
+	if o.dirCache != nil {
+		n, err := GenericReaddir(dirCtx, o.dirCache)
+		o.dirCacheMu.RUnlock()
+		return offset + n, err
+	}
+	o.dirCacheMu.RUnlock()
 
 	// readdirEntries holds o.copyUpMu to ensure that copy-up does not
-	// occur while calculating the readir results.
+	// occur while calculating the readdir results.
 	//
 	// However, it is possible for a copy-up to occur after the call to
-	// readdirEntries, but before setting f.dirCache. This is OK, since
-	// copy-up only does not change the children in a way that would affect
-	// the children returned in dirCache. Copy-up only moves
-	// files/directories between layers in the overlay.
+	// readdirEntries, but before setting o.dirCache. This is OK, since
+	// copy-up does not change the children in a way that would affect the
+	// children returned in dirCache. Copy-up only moves files/directories
+	// between layers in the overlay.
 	//
-	// It is also possible for Readdir to race with a Create operation
-	// (which may trigger a copy-up during it's execution). Depending on
-	// whether the Create happens before or after the readdirEntries call,
-	// the newly created file may or may not appear in the readdir results.
-	// But this can only be caused by a real race between readdir and
-	// create syscalls, so it's also OK.
-	dirCache, err := readdirEntries(ctx, o)
-	if err != nil {
-		return file.Offset(), err
+	// We must hold dirCacheMu around both readdirEntries and setting
+	// o.dirCache to synchronize with dirCache invalidations done by
+	// Create, Remove, Rename.
+	o.dirCacheMu.Lock()
+
+	// We expect dirCache to be nil (we just checked above), but there is a
+	// chance that a racing call managed to just set it, in which case we
+	// can use that new value.
+	if o.dirCache == nil {
+		dirCache, err := readdirEntries(ctx, o)
+		if err != nil {
+			o.dirCacheMu.Unlock()
+			return offset, err
+		}
+		o.dirCache = dirCache
 	}
 
-	f.dirCacheMu.Lock()
-	f.dirCache = dirCache
-	f.dirCacheMu.Unlock()
+	o.dirCacheMu.DowngradeLock()
+	n, err := GenericReaddir(dirCtx, o.dirCache)
+	o.dirCacheMu.RUnlock()
 
-	return DirentReaddir(ctx, file.Dirent, f, root, dirCtx, file.Offset())
-}
-
-// IterateDir implements DirIterator.IterateDir.
-func (f *overlayFileOperations) IterateDir(ctx context.Context, dirCtx *DirCtx, offset int) (int, error) {
-	f.dirCacheMu.RLock()
-	n, err := GenericReaddir(dirCtx, f.dirCache)
-	f.dirCacheMu.RUnlock()
 	return offset + n, err
 }
 
diff --git a/pkg/sentry/fs/fsutil/file.go b/pkg/sentry/fs/fsutil/file.go
index cca540b6c..d7ddc038b 100644
--- a/pkg/sentry/fs/fsutil/file.go
+++ b/pkg/sentry/fs/fsutil/file.go
@@ -285,7 +285,7 @@ func NewStaticDirFileOperations(dentries *fs.SortedDentryMap) *StaticDirFileOper
 }
 
 // IterateDir implements DirIterator.IterateDir.
-func (sdfo *StaticDirFileOperations) IterateDir(ctx context.Context, dirCtx *fs.DirCtx, offset int) (int, error) {
+func (sdfo *StaticDirFileOperations) IterateDir(ctx context.Context, d *fs.Dirent, dirCtx *fs.DirCtx, offset int) (int, error) {
 	n, err := fs.GenericReaddir(dirCtx, sdfo.dentryMap)
 	return offset + n, err
 }
diff --git a/pkg/sentry/fs/gofer/file.go b/pkg/sentry/fs/gofer/file.go
index ebbca162b..9e2e412cd 100644
--- a/pkg/sentry/fs/gofer/file.go
+++ b/pkg/sentry/fs/gofer/file.go
@@ -137,7 +137,7 @@ func (f *fileOperations) Readdir(ctx context.Context, file *fs.File, serializer
 }
 
 // IterateDir implements fs.DirIterator.IterateDir.
-func (f *fileOperations) IterateDir(ctx context.Context, dirCtx *fs.DirCtx, offset int) (int, error) {
+func (f *fileOperations) IterateDir(ctx context.Context, d *fs.Dirent, dirCtx *fs.DirCtx, offset int) (int, error) {
 	f.inodeOperations.readdirMu.Lock()
 	defer f.inodeOperations.readdirMu.Unlock()
 
diff --git a/pkg/sentry/fs/gofer/session.go b/pkg/sentry/fs/gofer/session.go
index 7ad0d8bc5..e9a07175a 100644
--- a/pkg/sentry/fs/gofer/session.go
+++ b/pkg/sentry/fs/gofer/session.go
@@ -145,16 +145,21 @@ func (s *session) Destroy() {
 	s.client.Close()
 }
 
-// Revalidate implements MountSource.Revalidate.
+// Revalidate implements MountSourceOperations.Revalidate.
 func (s *session) Revalidate(ctx context.Context, name string, parent, child *fs.Inode) bool {
 	return s.cachePolicy.revalidate(ctx, name, parent, child)
 }
 
-// Keep implements MountSource.Keep.
+// Keep implements MountSourceOperations.Keep.
 func (s *session) Keep(d *fs.Dirent) bool {
 	return s.cachePolicy.keep(d)
 }
 
+// CacheReaddir implements MountSourceOperations.CacheReaddir.
+func (s *session) CacheReaddir() bool {
+	return s.cachePolicy.cacheReaddir()
+}
+
 // ResetInodeMappings implements fs.MountSourceOperations.ResetInodeMappings.
 func (s *session) ResetInodeMappings() {
 	s.inodeMappings = make(map[uint64]string)
diff --git a/pkg/sentry/fs/host/file.go b/pkg/sentry/fs/host/file.go
index bd665a6b1..f6c626f2c 100644
--- a/pkg/sentry/fs/host/file.go
+++ b/pkg/sentry/fs/host/file.go
@@ -179,7 +179,7 @@ func (f *fileOperations) Readdir(ctx context.Context, file *fs.File, serializer
 }
 
 // IterateDir implements fs.DirIterator.IterateDir.
-func (f *fileOperations) IterateDir(ctx context.Context, dirCtx *fs.DirCtx, offset int) (int, error) {
+func (f *fileOperations) IterateDir(ctx context.Context, d *fs.Dirent, dirCtx *fs.DirCtx, offset int) (int, error) {
 	if f.dirinfo == nil {
 		f.dirinfo = new(dirInfo)
 		f.dirinfo.buf = make([]byte, usermem.PageSize)
diff --git a/pkg/sentry/fs/host/inode_test.go b/pkg/sentry/fs/host/inode_test.go
index 18994c456..2d959f10d 100644
--- a/pkg/sentry/fs/host/inode_test.go
+++ b/pkg/sentry/fs/host/inode_test.go
@@ -64,12 +64,12 @@ func TestMultipleReaddir(t *testing.T) {
 	defer openFile.DecRef()
 
 	c1 := &fs.DirCtx{DirCursor: new(string)}
-	if _, err := openFile.FileOperations.(*fileOperations).IterateDir(ctx, c1, 0); err != nil {
+	if _, err := openFile.FileOperations.(*fileOperations).IterateDir(ctx, dirent, c1, 0); err != nil {
 		t.Fatalf("First Readdir failed: %v", err)
 	}
 
 	c2 := &fs.DirCtx{DirCursor: new(string)}
-	if _, err := openFile.FileOperations.(*fileOperations).IterateDir(ctx, c2, 0); err != nil {
+	if _, err := openFile.FileOperations.(*fileOperations).IterateDir(ctx, dirent, c2, 0); err != nil {
 		t.Errorf("Second Readdir failed: %v", err)
 	}
 
diff --git a/pkg/sentry/fs/inode_overlay.go b/pkg/sentry/fs/inode_overlay.go
index 920d86042..b247fa514 100644
--- a/pkg/sentry/fs/inode_overlay.go
+++ b/pkg/sentry/fs/inode_overlay.go
@@ -217,6 +217,9 @@ func overlayCreate(ctx context.Context, o *overlayEntry, parent *Dirent, name st
 		return nil, err
 	}
 
+	// We've added to the directory so we must drop the cache.
+	o.markDirectoryDirty()
+
 	// Take another reference on the upper file's inode, which will be
 	// owned by the overlay entry.
 	upperFile.Dirent.Inode.IncRef()
@@ -265,7 +268,12 @@ func overlayCreateDirectory(ctx context.Context, o *overlayEntry, parent *Dirent
 	if err := copyUpLockedForRename(ctx, parent); err != nil {
 		return err
 	}
-	return o.upper.InodeOperations.CreateDirectory(ctx, o.upper, name, perm)
+	if err := o.upper.InodeOperations.CreateDirectory(ctx, o.upper, name, perm); err != nil {
+		return err
+	}
+	// We've added to the directory so we must drop the cache.
+	o.markDirectoryDirty()
+	return nil
 }
 
 func overlayCreateLink(ctx context.Context, o *overlayEntry, parent *Dirent, oldname string, newname string) error {
@@ -273,7 +281,12 @@ func overlayCreateLink(ctx context.Context, o *overlayEntry, parent *Dirent, old
 	if err := copyUpLockedForRename(ctx, parent); err != nil {
 		return err
 	}
-	return o.upper.InodeOperations.CreateLink(ctx, o.upper, oldname, newname)
+	if err := o.upper.InodeOperations.CreateLink(ctx, o.upper, oldname, newname); err != nil {
+		return err
+	}
+	// We've added to the directory so we must drop the cache.
+	o.markDirectoryDirty()
+	return nil
 }
 
 func overlayCreateHardLink(ctx context.Context, o *overlayEntry, parent *Dirent, target *Dirent, name string) error {
@@ -285,7 +298,12 @@ func overlayCreateHardLink(ctx context.Context, o *overlayEntry, parent *Dirent,
 	if err := copyUpLockedForRename(ctx, target); err != nil {
 		return err
 	}
-	return o.upper.InodeOperations.CreateHardLink(ctx, o.upper, target.Inode.overlay.upper, name)
+	if err := o.upper.InodeOperations.CreateHardLink(ctx, o.upper, target.Inode.overlay.upper, name); err != nil {
+		return err
+	}
+	// We've added to the directory so we must drop the cache.
+	o.markDirectoryDirty()
+	return nil
 }
 
 func overlayCreateFifo(ctx context.Context, o *overlayEntry, parent *Dirent, name string, perm FilePermissions) error {
@@ -293,7 +311,12 @@ func overlayCreateFifo(ctx context.Context, o *overlayEntry, parent *Dirent, nam
 	if err := copyUpLockedForRename(ctx, parent); err != nil {
 		return err
 	}
-	return o.upper.InodeOperations.CreateFifo(ctx, o.upper, name, perm)
+	if err := o.upper.InodeOperations.CreateFifo(ctx, o.upper, name, perm); err != nil {
+		return err
+	}
+	// We've added to the directory so we must drop the cache.
+	o.markDirectoryDirty()
+	return nil
 }
 
 func overlayRemove(ctx context.Context, o *overlayEntry, parent *Dirent, child *Dirent) error {
@@ -318,6 +341,8 @@ func overlayRemove(ctx context.Context, o *overlayEntry, parent *Dirent, child *
 	if child.Inode.overlay.lowerExists {
 		return overlayCreateWhiteout(o.upper, child.name)
 	}
+	// We've removed from the directory so we must drop the cache.
+	o.markDirectoryDirty()
 	return nil
 }
 
@@ -395,6 +420,8 @@ func overlayRename(ctx context.Context, o *overlayEntry, oldParent *Dirent, rena
 	if renamed.Inode.overlay.lowerExists {
 		return overlayCreateWhiteout(oldParent.Inode.overlay.upper, oldName)
 	}
+	// We've changed the directory so we must drop the cache.
+	o.markDirectoryDirty()
 	return nil
 }
 
@@ -411,6 +438,9 @@ func overlayBind(ctx context.Context, o *overlayEntry, parent *Dirent, name stri
 		return nil, err
 	}
 
+	// We've added to the directory so we must drop the cache.
+	o.markDirectoryDirty()
+
 	// Grab the inode and drop the dirent, we don't need it.
 	inode := d.Inode
 	inode.IncRef()
diff --git a/pkg/sentry/fs/mock.go b/pkg/sentry/fs/mock.go
index b3c4ad80b..7a24c6f1b 100644
--- a/pkg/sentry/fs/mock.go
+++ b/pkg/sentry/fs/mock.go
@@ -75,6 +75,12 @@ func (n *MockMountSourceOps) Keep(dirent *Dirent) bool {
 	return n.keep
 }
 
+// CacheReaddir implements fs.MountSourceOperations.CacheReaddir.
+func (n *MockMountSourceOps) CacheReaddir() bool {
+	// Common case: cache readdir results if there is a dirent cache.
+	return n.keep
+}
+
 // WriteOut implements fs.InodeOperations.WriteOut.
 func (n *MockInodeOperations) WriteOut(context.Context, *Inode) error {
 	return nil
diff --git a/pkg/sentry/fs/mount.go b/pkg/sentry/fs/mount.go
index 2eb6a9d82..912495528 100644
--- a/pkg/sentry/fs/mount.go
+++ b/pkg/sentry/fs/mount.go
@@ -23,8 +23,8 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/context"
 )
 
-// DirentOperations provide file systems greater control over how long a Dirent stays pinned
-// in core. Implementations must not take Dirent.mu.
+// DirentOperations provide file systems greater control over how long a Dirent
+// stays pinned in core. Implementations must not take Dirent.mu.
 type DirentOperations interface {
 	// Revalidate is called during lookup each time we encounter a Dirent
 	// in the cache. Implementations may update stale properties of the
@@ -37,6 +37,12 @@ type DirentOperations interface {
 	// Keep returns true if the Dirent should be kept in memory for as long
 	// as possible beyond any active references.
 	Keep(dirent *Dirent) bool
+
+	// CacheReaddir returns true if directory entries returned by
+	// FileOperations.Readdir may be cached for future use.
+	//
+	// Postconditions: This method must always return the same value.
+	CacheReaddir() bool
 }
 
 // MountSourceOperations contains filesystem specific operations.
@@ -190,25 +196,28 @@ func (msrc *MountSource) SetDirentCacheLimiter(l *DirentCacheLimiter) {
 // aggressively.
 func NewCachingMountSource(ctx context.Context, filesystem Filesystem, flags MountSourceFlags) *MountSource {
 	return NewMountSource(ctx, &SimpleMountSourceOperations{
-		keep:       true,
-		revalidate: false,
+		keep:         true,
+		revalidate:   false,
+		cacheReaddir: true,
 	}, filesystem, flags)
 }
 
 // NewNonCachingMountSource returns a generic mount that will never cache dirents.
 func NewNonCachingMountSource(ctx context.Context, filesystem Filesystem, flags MountSourceFlags) *MountSource {
 	return NewMountSource(ctx, &SimpleMountSourceOperations{
-		keep:       false,
-		revalidate: false,
+		keep:         false,
+		revalidate:   false,
+		cacheReaddir: false,
 	}, filesystem, flags)
 }
 
 // NewRevalidatingMountSource returns a generic mount that will cache dirents,
-// but will revalidate them on each lookup.
+// but will revalidate them on each lookup and always perform uncached readdir.
 func NewRevalidatingMountSource(ctx context.Context, filesystem Filesystem, flags MountSourceFlags) *MountSource {
 	return NewMountSource(ctx, &SimpleMountSourceOperations{
-		keep:       true,
-		revalidate: true,
+		keep:         true,
+		revalidate:   true,
+		cacheReaddir: false,
 	}, filesystem, flags)
 }
 
@@ -216,8 +225,9 @@ func NewRevalidatingMountSource(ctx context.Context, filesystem Filesystem, flag
 // an actual filesystem. It is always non-caching.
 func NewPseudoMountSource(ctx context.Context) *MountSource {
 	return NewMountSource(ctx, &SimpleMountSourceOperations{
-		keep:       false,
-		revalidate: false,
+		keep:         false,
+		revalidate:   false,
+		cacheReaddir: false,
 	}, nil, MountSourceFlags{})
 }
 
@@ -225,8 +235,9 @@ func NewPseudoMountSource(ctx context.Context) *MountSource {
 //
 // +stateify savable
 type SimpleMountSourceOperations struct {
-	keep       bool
-	revalidate bool
+	keep         bool
+	revalidate   bool
+	cacheReaddir bool
 }
 
 // Revalidate implements MountSourceOperations.Revalidate.
@@ -239,6 +250,11 @@ func (smo *SimpleMountSourceOperations) Keep(*Dirent) bool {
 	return smo.keep
 }
 
+// CacheReaddir implements MountSourceOperations.CacheReaddir.
+func (smo *SimpleMountSourceOperations) CacheReaddir() bool {
+	return smo.cacheReaddir
+}
+
 // ResetInodeMappings implements MountSourceOperations.ResetInodeMappings.
 func (*SimpleMountSourceOperations) ResetInodeMappings() {}
 
diff --git a/pkg/sentry/fs/mount_overlay.go b/pkg/sentry/fs/mount_overlay.go
index bc0ce7adc..4fcdd6c01 100644
--- a/pkg/sentry/fs/mount_overlay.go
+++ b/pkg/sentry/fs/mount_overlay.go
@@ -81,6 +81,17 @@ func (o *overlayMountSourceOperations) Keep(dirent *Dirent) bool {
 	return o.upper.Keep(dirent)
 }
 
+// CacheReaddir implements MountSourceOperations.CacheReaddir for an overlay by
+// performing the logical AND of the upper and lower filesystems' CacheReaddir
+// methods.
+//
+// N.B. This is fs-global instead of inode-specific because it must always
+// return the same value. If it was inode-specific, we couldn't guarantee that
+// property across copy up.
+func (o *overlayMountSourceOperations) CacheReaddir() bool {
+	return o.lower.CacheReaddir() && o.upper.CacheReaddir()
+}
+
 // ResetInodeMappings propagates the call to both upper and lower MountSource.
 func (o *overlayMountSourceOperations) ResetInodeMappings() {
 	o.upper.ResetInodeMappings()
diff --git a/pkg/sentry/fs/overlay.go b/pkg/sentry/fs/overlay.go
index c87f24997..1d3ff39e0 100644
--- a/pkg/sentry/fs/overlay.go
+++ b/pkg/sentry/fs/overlay.go
@@ -24,6 +24,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
 	"gvisor.dev/gvisor/pkg/sentry/usermem"
 	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/third_party/gvsync"
 )
 
 // The virtual filesystem implements an overlay configuration. For a high-level
@@ -196,6 +197,12 @@ type overlayEntry struct {
 	// these locks is sufficient to read upper; holding all three for writing
 	// is required to mutate it.
 	upper *Inode
+
+	// dirCacheMu protects dirCache.
+	dirCacheMu gvsync.DowngradableRWMutex `state:"nosave"`
+
+	// dirCache is cache of DentAttrs from upper and lower Inodes.
+	dirCache *SortedDentryMap
 }
 
 // newOverlayEntry returns a new overlayEntry.
@@ -258,6 +265,17 @@ func (o *overlayEntry) isMappableLocked() bool {
 	return o.inodeLocked().Mappable() != nil
 }
 
+// markDirectoryDirty marks any cached data dirty for this directory. This is
+// necessary in order to ensure that this node does not retain stale state
+// throughout its lifetime across multiple open directory handles.
+//
+// Currently this means invalidating any readdir caches.
+func (o *overlayEntry) markDirectoryDirty() {
+	o.dirCacheMu.Lock()
+	o.dirCache = nil
+	o.dirCacheMu.Unlock()
+}
+
 // AddMapping implements memmap.Mappable.AddMapping.
 func (o *overlayEntry) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) error {
 	o.mapsMu.Lock()
diff --git a/pkg/sentry/fs/ramfs/dir.go b/pkg/sentry/fs/ramfs/dir.go
index 0c9e6ec09..f3e984c24 100644
--- a/pkg/sentry/fs/ramfs/dir.go
+++ b/pkg/sentry/fs/ramfs/dir.go
@@ -431,7 +431,7 @@ func (dfo *dirFileOperations) Seek(ctx context.Context, file *fs.File, whence fs
 }
 
 // IterateDir implements DirIterator.IterateDir.
-func (dfo *dirFileOperations) IterateDir(ctx context.Context, dirCtx *fs.DirCtx, offset int) (int, error) {
+func (dfo *dirFileOperations) IterateDir(ctx context.Context, d *fs.Dirent, dirCtx *fs.DirCtx, offset int) (int, error) {
 	dfo.dir.mu.Lock()
 	defer dfo.dir.mu.Unlock()
 
diff --git a/pkg/sentry/fs/tty/dir.go b/pkg/sentry/fs/tty/dir.go
index 58a26742c..1d128532b 100644
--- a/pkg/sentry/fs/tty/dir.go
+++ b/pkg/sentry/fs/tty/dir.go
@@ -307,7 +307,7 @@ type dirFileOperations struct {
 var _ fs.FileOperations = (*dirFileOperations)(nil)
 
 // IterateDir implements DirIterator.IterateDir.
-func (df *dirFileOperations) IterateDir(ctx context.Context, dirCtx *fs.DirCtx, offset int) (int, error) {
+func (df *dirFileOperations) IterateDir(ctx context.Context, d *fs.Dirent, dirCtx *fs.DirCtx, offset int) (int, error) {
 	df.di.mu.Lock()
 	defer df.di.mu.Unlock()
 
diff --git a/pkg/sentry/fs/tty/fs.go b/pkg/sentry/fs/tty/fs.go
index 1bbfbb90a..edee56c12 100644
--- a/pkg/sentry/fs/tty/fs.go
+++ b/pkg/sentry/fs/tty/fs.go
@@ -94,6 +94,13 @@ func (superOperations) Keep(*fs.Dirent) bool {
 	return false
 }
 
+// CacheReaddir implements fs.DirentOperations.CacheReaddir.
+//
+// CacheReaddir returns false because entries change on master operations.
+func (superOperations) CacheReaddir() bool {
+	return false
+}
+
 // ResetInodeMappings implements MountSourceOperations.ResetInodeMappings.
 func (superOperations) ResetInodeMappings() {}
 
-- 
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