Mix checklocks and atomic analyzers.

This change makes the checklocks analyzer considerable more powerful, adding:
* The ability to traverse complex structures, e.g. to have multiple nested
  fields as part of the annotation.
* The ability to resolve simple anonymous functions and closures, and perform
  lock analysis across these invocations. This does not apply to closures that
  are passed elsewhere, since it is not possible to know the context in which
  they might be invoked.
* The ability to annotate return values in addition to receivers and other
  parameters, with the same complex structures noted above.
* Ignoring locking semantics for "fresh" objects, i.e. objects that are
  allocated in the local frame (typically a new-style function).
* Sanity checking of locking state across block transitions and returns, to
  ensure that no unexpected locks are held.

Note that initially, most of these findings are excluded by a comprehensive
nogo.yaml. The findings that are included are fundamental lock violations.
The changes here should be relatively low risk, minor refactorings to either
include necessary annotations to simplify the code structure (in general
removing closures in favor of methods) so that the analyzer can be easily
track the lock state.

This change additional includes two changes to nogo itself:
* Sanity checking of all types to ensure that the binary and ast-derived
  types have a consistent objectpath, to prevent the bug above from occurring
  silently (and causing much confusion). This also requires a trick in
  order to ensure that serialized facts are consumable downstream. This can
  be removed with https://go-review.googlesource.com/c/tools/+/331789 merged.
* A minor refactoring to isolation the objdump settings in its own package.
  This was originally used to implement the sanity check above, but this
  information is now being passed another way. The minor refactor is preserved
  however, since it cleans up the code slightly and is minimal risk.

PiperOrigin-RevId: 382613300

6 files changed, 131 insertions, 95 deletions

diff --git a/pkg/sentry/fs/dirent.go b/pkg/sentry/fs/dirent.go
index 3a45e9041..8d7660e79 100644
--- a/pkg/sentry/fs/dirent.go
+++ b/pkg/sentry/fs/dirent.go
@@ -488,11 +488,11 @@ func (d *Dirent) walk(ctx context.Context, root *Dirent, name string, walkMayUnl
 	// Slow path: load the InodeOperations into memory. Since this is a hot path and the lookup may be
 	// expensive, if possible release the lock and re-acquire it.
 	if walkMayUnlock {
-		d.mu.Unlock()
+		d.mu.Unlock() // +checklocksforce: results in an inconsistent block.
 	}
 	c, err := d.Inode.Lookup(ctx, name)
 	if walkMayUnlock {
-		d.mu.Lock()
+		d.mu.Lock() // +checklocksforce: see above.
 	}
 	// No dice.
 	if err != nil {
@@ -594,21 +594,27 @@ func (d *Dirent) exists(ctx context.Context, root *Dirent, name string) bool {
 
 // lockDirectory should be called for any operation that changes this `d`s
 // children (creating or removing them).
-func (d *Dirent) lockDirectory() func() {
+// +checklocksacquire:d.dirMu
+// +checklocksacquire:d.mu
+func (d *Dirent) lockDirectory() {
 	renameMu.RLock()
 	d.dirMu.Lock()
 	d.mu.Lock()
-	return func() {
-		d.mu.Unlock()
-		d.dirMu.Unlock()
-		renameMu.RUnlock()
-	}
+}
+
+// unlockDirectory is the reverse of lockDirectory.
+// +checklocksrelease:d.dirMu
+// +checklocksrelease:d.mu
+func (d *Dirent) unlockDirectory() {
+	d.mu.Unlock()
+	d.dirMu.Unlock()
+	renameMu.RUnlock() // +checklocksforce: see lockDirectory.
 }
 
 // Create creates a new regular file in this directory.
 func (d *Dirent) Create(ctx context.Context, root *Dirent, name string, flags FileFlags, perms FilePermissions) (*File, error) {
-	unlock := d.lockDirectory()
-	defer unlock()
+	d.lockDirectory()
+	defer d.unlockDirectory()
 
 	// Does something already exist?
 	if d.exists(ctx, root, name) {
@@ -670,8 +676,8 @@ func (d *Dirent) finishCreate(ctx context.Context, child *Dirent, name string) {
 // genericCreate executes create if name does not exist. Removes a negative Dirent at name if
 // create succeeds.
 func (d *Dirent) genericCreate(ctx context.Context, root *Dirent, name string, create func() error) error {
-	unlock := d.lockDirectory()
-	defer unlock()
+	d.lockDirectory()
+	defer d.unlockDirectory()
 
 	// Does something already exist?
 	if d.exists(ctx, root, name) {
@@ -1021,8 +1027,8 @@ func (d *Dirent) Remove(ctx context.Context, root *Dirent, name string, dirPath
 		panic("Dirent.Remove: root must not be nil")
 	}
 
-	unlock := d.lockDirectory()
-	defer unlock()
+	d.lockDirectory()
+	defer d.unlockDirectory()
 
 	// Try to walk to the node.
 	child, err := d.walk(ctx, root, name, false /* may unlock */)
@@ -1082,8 +1088,8 @@ func (d *Dirent) RemoveDirectory(ctx context.Context, root *Dirent, name string)
 		panic("Dirent.Remove: root must not be nil")
 	}
 
-	unlock := d.lockDirectory()
-	defer unlock()
+	d.lockDirectory()
+	defer d.unlockDirectory()
 
 	// Check for dots.
 	if name == "." {
@@ -1259,17 +1265,15 @@ func (d *Dirent) dropExtendedReference() {
 	d.Inode.MountSource.fscache.Remove(d)
 }
 
-// lockForRename takes locks on oldParent and newParent as required by Rename
-// and returns a function that will unlock the locks taken. The returned
-// function must be called even if a non-nil error is returned.
-func lockForRename(oldParent *Dirent, oldName string, newParent *Dirent, newName string) (func(), error) {
+// lockForRename takes locks on oldParent and newParent as required by Rename.
+// On return, unlockForRename must always be called, even with an error.
+// +checklocksacquire:oldParent.mu
+// +checklocksacquire:newParent.mu
+func lockForRename(oldParent *Dirent, oldName string, newParent *Dirent, newName string) error {
 	renameMu.Lock()
 	if oldParent == newParent {
 		oldParent.mu.Lock()
-		return func() {
-			oldParent.mu.Unlock()
-			renameMu.Unlock()
-		}, nil
+		return nil // +checklocksforce: only one lock exists.
 	}
 
 	// Renaming between directories is a bit subtle:
@@ -1297,11 +1301,7 @@ func lockForRename(oldParent *Dirent, oldName string, newParent *Dirent, newName
 				// itself.
 				err = unix.EINVAL
 			}
-			return func() {
-				newParent.mu.Unlock()
-				oldParent.mu.Unlock()
-				renameMu.Unlock()
-			}, err
+			return err
 		}
 		child = p
 	}
@@ -1310,11 +1310,21 @@ func lockForRename(oldParent *Dirent, oldName string, newParent *Dirent, newName
 	// have no relationship; in either case we can do this:
 	newParent.mu.Lock()
 	oldParent.mu.Lock()
-	return func() {
+	return nil
+}
+
+// unlockForRename is the opposite of lockForRename.
+// +checklocksrelease:oldParent.mu
+// +checklocksrelease:newParent.mu
+func unlockForRename(oldParent, newParent *Dirent) {
+	if oldParent == newParent {
 		oldParent.mu.Unlock()
-		newParent.mu.Unlock()
-		renameMu.Unlock()
-	}, nil
+		renameMu.Unlock() // +checklocksforce: only one lock exists.
+		return
+	}
+	newParent.mu.Unlock()
+	oldParent.mu.Unlock()
+	renameMu.Unlock() // +checklocksforce: not tracked.
 }
 
 func (d *Dirent) checkSticky(ctx context.Context, victim *Dirent) error {
@@ -1353,8 +1363,8 @@ func (d *Dirent) MayDelete(ctx context.Context, root *Dirent, name string) error
 		return err
 	}
 
-	unlock := d.lockDirectory()
-	defer unlock()
+	d.lockDirectory()
+	defer d.unlockDirectory()
 
 	victim, err := d.walk(ctx, root, name, true /* may unlock */)
 	if err != nil {
@@ -1392,8 +1402,8 @@ func Rename(ctx context.Context, root *Dirent, oldParent *Dirent, oldName string
 	}
 
 	// Acquire global renameMu lock, and mu locks on oldParent/newParent.
-	unlock, err := lockForRename(oldParent, oldName, newParent, newName)
-	defer unlock()
+	err := lockForRename(oldParent, oldName, newParent, newName)
+	defer unlockForRename(oldParent, newParent)
 	if err != nil {
 		return err
 	}
diff --git a/pkg/sentry/fs/fs.go b/pkg/sentry/fs/fs.go
index 44587bb37..a346c316b 100644
--- a/pkg/sentry/fs/fs.go
+++ b/pkg/sentry/fs/fs.go
@@ -80,23 +80,33 @@ func AsyncBarrier() {
 // Async executes a function asynchronously.
 //
 // Async must not be called recursively.
+// +checklocksignore
 func Async(f func()) {
 	workMu.RLock()
-	go func() { // S/R-SAFE: AsyncBarrier must be called.
-		defer workMu.RUnlock() // Ensure RUnlock in case of panic.
-		f()
-	}()
+	go asyncWork(f) // S/R-SAFE: AsyncBarrier must be called.
+}
+
+// +checklocksignore
+func asyncWork(f func()) {
+	// Ensure RUnlock in case of panic.
+	defer workMu.RUnlock()
+	f()
 }
 
 // AsyncWithContext is just like Async, except that it calls the asynchronous
 // function with the given context as argument. This function exists to avoid
 // needing to allocate an extra function on the heap in a hot path.
+// +checklocksignore
 func AsyncWithContext(ctx context.Context, f func(context.Context)) {
 	workMu.RLock()
-	go func() { // S/R-SAFE: AsyncBarrier must be called.
-		defer workMu.RUnlock() // Ensure RUnlock in case of panic.
-		f(ctx)
-	}()
+	go asyncWorkWithContext(ctx, f)
+}
+
+// +checklocksignore
+func asyncWorkWithContext(ctx context.Context, f func(context.Context)) {
+	// Ensure RUnlock in case of panic.
+	defer workMu.RUnlock()
+	f(ctx)
 }
 
 // AsyncErrorBarrier waits for all outstanding asynchronous work to complete, or
diff --git a/pkg/sentry/fs/gofer/inode_state.go b/pkg/sentry/fs/gofer/inode_state.go
index e2af1d2ae..19f91f010 100644
--- a/pkg/sentry/fs/gofer/inode_state.go
+++ b/pkg/sentry/fs/gofer/inode_state.go
@@ -112,13 +112,6 @@ func (i *inodeFileState) loadLoading(_ struct{}) {
 // +checklocks:i.loading
 func (i *inodeFileState) afterLoad() {
 	load := func() (err error) {
-		// See comment on i.loading().
-		defer func() {
-			if err == nil {
-				i.loading.Unlock()
-			}
-		}()
-
 		// Manually restore the p9.File.
 		name, ok := i.s.inodeMappings[i.sattr.InodeID]
 		if !ok {
@@ -167,6 +160,9 @@ func (i *inodeFileState) afterLoad() {
 			i.savedUAttr = nil
 		}
 
+		// See comment on i.loading(). This only unlocks on the
+		// non-error path.
+		i.loading.Unlock() // +checklocksforce: per comment.
 		return nil
 	}
 
diff --git a/pkg/sentry/fs/gofer/path.go b/pkg/sentry/fs/gofer/path.go
index aa2405f68..958f46bd6 100644
--- a/pkg/sentry/fs/gofer/path.go
+++ b/pkg/sentry/fs/gofer/path.go
@@ -47,7 +47,8 @@ func (i *inodeOperations) Lookup(ctx context.Context, dir *fs.Inode, name string
 		return nil, linuxerr.ENAMETOOLONG
 	}
 
-	cp := i.session().cachePolicy
+	s := i.session()
+	cp := s.cachePolicy
 	if cp.cacheReaddir() {
 		// Check to see if we have readdirCache that indicates the
 		// child does not exist.  Avoid holding readdirMu longer than
@@ -78,7 +79,7 @@ func (i *inodeOperations) Lookup(ctx context.Context, dir *fs.Inode, name string
 		return nil, err
 	}
 
-	if i.session().overrides != nil {
+	if s.overrides != nil {
 		// Check if file belongs to a internal named pipe. Note that it doesn't need
 		// to check for sockets because it's done in newInodeOperations below.
 		deviceKey := device.MultiDeviceKey{
@@ -86,13 +87,13 @@ func (i *inodeOperations) Lookup(ctx context.Context, dir *fs.Inode, name string
 			SecondaryDevice: i.session().connID,
 			Inode:           qids[0].Path,
 		}
-		unlock := i.session().overrides.lock()
-		if pipeInode := i.session().overrides.getPipe(deviceKey); pipeInode != nil {
-			unlock()
+		s.overrides.lock()
+		if pipeInode := s.overrides.getPipe(deviceKey); pipeInode != nil {
+			s.overrides.unlock()
 			pipeInode.IncRef()
 			return fs.NewDirent(ctx, pipeInode, name), nil
 		}
-		unlock()
+		s.overrides.unlock()
 	}
 
 	// Construct the Inode operations.
@@ -221,17 +222,20 @@ func (i *inodeOperations) CreateHardLink(ctx context.Context, inode *fs.Inode, t
 	if err := i.fileState.file.link(ctx, &targetOpts.fileState.file, newName); err != nil {
 		return err
 	}
-	if i.session().cachePolicy.cacheUAttrs(inode) {
+
+	s := i.session()
+	if s.cachePolicy.cacheUAttrs(inode) {
 		// Increase link count.
 		targetOpts.cachingInodeOps.IncLinks(ctx)
 	}
+
 	i.touchModificationAndStatusChangeTime(ctx, inode)
 	return nil
 }
 
 // CreateDirectory uses Create to create a directory named s under inodeOperations.
-func (i *inodeOperations) CreateDirectory(ctx context.Context, dir *fs.Inode, s string, perm fs.FilePermissions) error {
-	if len(s) > maxFilenameLen {
+func (i *inodeOperations) CreateDirectory(ctx context.Context, dir *fs.Inode, name string, perm fs.FilePermissions) error {
+	if len(name) > maxFilenameLen {
 		return linuxerr.ENAMETOOLONG
 	}
 
@@ -247,16 +251,18 @@ func (i *inodeOperations) CreateDirectory(ctx context.Context, dir *fs.Inode, s
 		perm.SetGID = true
 	}
 
-	if _, err := i.fileState.file.mkdir(ctx, s, p9.FileMode(perm.LinuxMode()), p9.UID(owner.UID), p9.GID(owner.GID)); err != nil {
+	if _, err := i.fileState.file.mkdir(ctx, name, p9.FileMode(perm.LinuxMode()), p9.UID(owner.UID), p9.GID(owner.GID)); err != nil {
 		return err
 	}
-	if i.session().cachePolicy.cacheUAttrs(dir) {
+
+	s := i.session()
+	if s.cachePolicy.cacheUAttrs(dir) {
 		// Increase link count.
 		//
 		// N.B. This will update the modification time.
 		i.cachingInodeOps.IncLinks(ctx)
 	}
-	if i.session().cachePolicy.cacheReaddir() {
+	if s.cachePolicy.cacheReaddir() {
 		// Invalidate readdir cache.
 		i.markDirectoryDirty()
 	}
@@ -269,13 +275,14 @@ func (i *inodeOperations) Bind(ctx context.Context, dir *fs.Inode, name string,
 		return nil, linuxerr.ENAMETOOLONG
 	}
 
-	if i.session().overrides == nil {
+	s := i.session()
+	if s.overrides == nil {
 		return nil, syserror.EOPNOTSUPP
 	}
 
 	// Stabilize the override map while creation is in progress.
-	unlock := i.session().overrides.lock()
-	defer unlock()
+	s.overrides.lock()
+	defer s.overrides.unlock()
 
 	sattr, iops, err := i.createEndpointFile(ctx, dir, name, perm, p9.ModeSocket)
 	if err != nil {
@@ -284,7 +291,7 @@ func (i *inodeOperations) Bind(ctx context.Context, dir *fs.Inode, name string,
 
 	// Construct the positive Dirent.
 	childDir := fs.NewDirent(ctx, fs.NewInode(ctx, iops, dir.MountSource, sattr), name)
-	i.session().overrides.addBoundEndpoint(iops.fileState.key, childDir, ep)
+	s.overrides.addBoundEndpoint(iops.fileState.key, childDir, ep)
 	return childDir, nil
 }
 
@@ -298,8 +305,9 @@ func (i *inodeOperations) CreateFifo(ctx context.Context, dir *fs.Inode, name st
 	mode := p9.FileMode(perm.LinuxMode()) | p9.ModeNamedPipe
 
 	// N.B. FIFOs use major/minor numbers 0.
+	s := i.session()
 	if _, err := i.fileState.file.mknod(ctx, name, mode, 0, 0, p9.UID(owner.UID), p9.GID(owner.GID)); err != nil {
-		if i.session().overrides == nil || !linuxerr.Equals(linuxerr.EPERM, err) {
+		if s.overrides == nil || !linuxerr.Equals(linuxerr.EPERM, err) {
 			return err
 		}
 		// If gofer doesn't support mknod, check if we can create an internal fifo.
@@ -311,13 +319,14 @@ func (i *inodeOperations) CreateFifo(ctx context.Context, dir *fs.Inode, name st
 }
 
 func (i *inodeOperations) createInternalFifo(ctx context.Context, dir *fs.Inode, name string, owner fs.FileOwner, perm fs.FilePermissions) error {
-	if i.session().overrides == nil {
+	s := i.session()
+	if s.overrides == nil {
 		return linuxerr.EPERM
 	}
 
 	// Stabilize the override map while creation is in progress.
-	unlock := i.session().overrides.lock()
-	defer unlock()
+	s.overrides.lock()
+	defer s.overrides.unlock()
 
 	sattr, fileOps, err := i.createEndpointFile(ctx, dir, name, perm, p9.ModeNamedPipe)
 	if err != nil {
@@ -336,7 +345,7 @@ func (i *inodeOperations) createInternalFifo(ctx context.Context, dir *fs.Inode,
 
 	// Construct the positive Dirent.
 	childDir := fs.NewDirent(ctx, fs.NewInode(ctx, iops, dir.MountSource, sattr), name)
-	i.session().overrides.addPipe(fileOps.fileState.key, childDir, inode)
+	s.overrides.addPipe(fileOps.fileState.key, childDir, inode)
 	return nil
 }
 
@@ -386,8 +395,9 @@ func (i *inodeOperations) Remove(ctx context.Context, dir *fs.Inode, name string
 		return linuxerr.ENAMETOOLONG
 	}
 
+	s := i.session()
 	var key *device.MultiDeviceKey
-	if i.session().overrides != nil {
+	if s.overrides != nil {
 		// Find out if file being deleted is a socket or pipe that needs to be
 		// removed from endpoint map.
 		if d, err := i.Lookup(ctx, dir, name); err == nil {
@@ -402,8 +412,8 @@ func (i *inodeOperations) Remove(ctx context.Context, dir *fs.Inode, name string
 				}
 
 				// Stabilize the override map while deletion is in progress.
-				unlock := i.session().overrides.lock()
-				defer unlock()
+				s.overrides.lock()
+				defer s.overrides.unlock()
 			}
 		}
 	}
@@ -412,7 +422,7 @@ func (i *inodeOperations) Remove(ctx context.Context, dir *fs.Inode, name string
 		return err
 	}
 	if key != nil {
-		i.session().overrides.remove(ctx, *key)
+		s.overrides.remove(ctx, *key)
 	}
 	i.touchModificationAndStatusChangeTime(ctx, dir)
 
@@ -429,11 +439,13 @@ func (i *inodeOperations) RemoveDirectory(ctx context.Context, dir *fs.Inode, na
 	if err := i.fileState.file.unlinkAt(ctx, name, 0x200); err != nil {
 		return err
 	}
-	if i.session().cachePolicy.cacheUAttrs(dir) {
+
+	s := i.session()
+	if s.cachePolicy.cacheUAttrs(dir) {
 		// Decrease link count and updates atime.
 		i.cachingInodeOps.DecLinks(ctx)
 	}
-	if i.session().cachePolicy.cacheReaddir() {
+	if s.cachePolicy.cacheReaddir() {
 		// Invalidate readdir cache.
 		i.markDirectoryDirty()
 	}
@@ -463,12 +475,13 @@ func (i *inodeOperations) Rename(ctx context.Context, inode *fs.Inode, oldParent
 	}
 
 	// Is the renamed entity a directory? Fix link counts.
+	s := i.session()
 	if fs.IsDir(i.fileState.sattr) {
 		// Update cached state.
-		if i.session().cachePolicy.cacheUAttrs(oldParent) {
+		if s.cachePolicy.cacheUAttrs(oldParent) {
 			oldParentInodeOperations.cachingInodeOps.DecLinks(ctx)
 		}
-		if i.session().cachePolicy.cacheUAttrs(newParent) {
+		if s.cachePolicy.cacheUAttrs(newParent) {
 			// Only IncLinks if there is a new addition to
 			// newParent. If this is replacement, then the total
 			// count remains the same.
@@ -477,7 +490,7 @@ func (i *inodeOperations) Rename(ctx context.Context, inode *fs.Inode, oldParent
 			}
 		}
 	}
-	if i.session().cachePolicy.cacheReaddir() {
+	if s.cachePolicy.cacheReaddir() {
 		// Mark old directory dirty.
 		oldParentInodeOperations.markDirectoryDirty()
 		if oldParent != newParent {
@@ -487,17 +500,18 @@ func (i *inodeOperations) Rename(ctx context.Context, inode *fs.Inode, oldParent
 	}
 
 	// Rename always updates ctime.
-	if i.session().cachePolicy.cacheUAttrs(inode) {
+	if s.cachePolicy.cacheUAttrs(inode) {
 		i.cachingInodeOps.TouchStatusChangeTime(ctx)
 	}
 	return nil
 }
 
 func (i *inodeOperations) touchModificationAndStatusChangeTime(ctx context.Context, inode *fs.Inode) {
-	if i.session().cachePolicy.cacheUAttrs(inode) {
+	s := i.session()
+	if s.cachePolicy.cacheUAttrs(inode) {
 		i.cachingInodeOps.TouchModificationAndStatusChangeTime(ctx)
 	}
-	if i.session().cachePolicy.cacheReaddir() {
+	if s.cachePolicy.cacheReaddir() {
 		// Invalidate readdir cache.
 		i.markDirectoryDirty()
 	}
diff --git a/pkg/sentry/fs/gofer/session.go b/pkg/sentry/fs/gofer/session.go
index 7cf3522ff..b7debeecb 100644
--- a/pkg/sentry/fs/gofer/session.go
+++ b/pkg/sentry/fs/gofer/session.go
@@ -98,9 +98,14 @@ func (e *overrideMaps) remove(ctx context.Context, key device.MultiDeviceKey) {
 // lock blocks other addition and removal operations from happening while
 // the backing file is being created or deleted. Returns a function that unlocks
 // the endpoint map.
-func (e *overrideMaps) lock() func() {
+// +checklocksacquire:e.mu
+func (e *overrideMaps) lock() {
 	e.mu.Lock()
-	return func() { e.mu.Unlock() }
+}
+
+// +checklocksrelease:e.mu
+func (e *overrideMaps) unlock() {
+	e.mu.Unlock()
 }
 
 // getBoundEndpoint returns the bound endpoint mapped to the given key.
@@ -366,8 +371,8 @@ func newOverrideMaps() *overrideMaps {
 
 // fillKeyMap populates key and dirent maps upon restore from saved pathmap.
 func (s *session) fillKeyMap(ctx context.Context) error {
-	unlock := s.overrides.lock()
-	defer unlock()
+	s.overrides.lock()
+	defer s.overrides.unlock()
 
 	for ep, dirPath := range s.overrides.pathMap {
 		_, file, err := s.attach.walk(ctx, splitAbsolutePath(dirPath))
@@ -394,8 +399,8 @@ func (s *session) fillKeyMap(ctx context.Context) error {
 // fillPathMap populates paths for overrides from dirents in direntMap
 // before save.
 func (s *session) fillPathMap(ctx context.Context) error {
-	unlock := s.overrides.lock()
-	defer unlock()
+	s.overrides.lock()
+	defer s.overrides.unlock()
 
 	for _, endpoint := range s.overrides.keyMap {
 		mountRoot := endpoint.dirent.MountRoot()
diff --git a/pkg/sentry/fs/gofer/socket.go b/pkg/sentry/fs/gofer/socket.go
index 8a1c69ac2..1fd8a0910 100644
--- a/pkg/sentry/fs/gofer/socket.go
+++ b/pkg/sentry/fs/gofer/socket.go
@@ -32,10 +32,11 @@ func (i *inodeOperations) BoundEndpoint(inode *fs.Inode, path string) transport.
 		return nil
 	}
 
-	if i.session().overrides != nil {
-		unlock := i.session().overrides.lock()
-		defer unlock()
-		ep := i.session().overrides.getBoundEndpoint(i.fileState.key)
+	s := i.session()
+	if s.overrides != nil {
+		s.overrides.lock()
+		defer s.overrides.unlock()
+		ep := s.overrides.getBoundEndpoint(i.fileState.key)
 		if ep != nil {
 			return ep
 		}