archiver: Fix race condition triggered by TestArchiverAbortEarlyOnError

The Save methods of the BlobSaver, FileSaver and TreeSaver return early
on when the archiver is stopped due to an error. For that they select on
both the tomb.Dying() and context.Done() channels, which can lead to a
race condition when the tomb is killed due to an error: The tomb first
closes its Dying channel before canceling all child contexts.
Archiver.SaveDir only aborts its execution once the context was
canceled. When the tomb killing is paused between closing its Dying
channel and canceling the child contexts, this lets the
FileSaver/TreeSaver.Save methods return immediately, however, ScanDir
still reads further files causing the test case to fail.

As a killed tomb always cancels all child contexts and as the Savers
always use a context bound to the tomb, it is sufficient to just use
context.Done() as escape hatch in the Save functions. This fixes the
mismatch between SaveDir and Save.

Adjust the tests to use contexts bound to the tomb for all interactions
with the Savers.

internal/archiver/blob_saver.go

@@ -22,8 +22,7 @@ type BlobSaver struct {
 	m          sync.Mutex
 	knownBlobs restic.BlobSet
 
-	ch   chan<- saveBlobJob
-	done <-chan struct{}
+	ch chan<- saveBlobJob
 }
 
 // NewBlobSaver returns a new blob. A worker pool is started, it is stopped
@@ -34,7 +33,6 @@ func NewBlobSaver(ctx context.Context, t *tomb.Tomb, repo Saver, workers uint) *
 		repo:       repo,
 		knownBlobs: restic.NewBlobSet(),
 		ch:         ch,
-		done:       t.Dying(),
 	}
 
 	for i := uint(0); i < workers; i++ {
@@ -53,10 +51,6 @@ func (s *BlobSaver) Save(ctx context.Context, t restic.BlobType, buf *Buffer) Fu
 	ch := make(chan saveBlobResponse, 1)
 	select {
 	case s.ch <- saveBlobJob{BlobType: t, buf: buf, ch: ch}:
-	case <-s.done:
-		debug.Log("not sending job, BlobSaver is done")
-		close(ch)
-		return FutureBlob{ch: ch}
 	case <-ctx.Done():
 		debug.Log("not sending job, context is cancelled")
 		close(ch)

internal/archiver/blob_saver_test.go

@@ -38,12 +38,12 @@ func TestBlobSaver(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
-	var tmb tomb.Tomb
+	tmb, ctx := tomb.WithContext(ctx)
 	saver := &saveFail{
 		idx: repository.NewIndex(),
 	}
 
-	b := NewBlobSaver(ctx, &tmb, saver, uint(runtime.NumCPU()))
+	b := NewBlobSaver(ctx, tmb, saver, uint(runtime.NumCPU()))
 
 	var results []FutureBlob
 
@@ -84,13 +84,13 @@ func TestBlobSaverError(t *testing.T) {
 			ctx, cancel := context.WithCancel(context.Background())
 			defer cancel()
 
-			var tmb tomb.Tomb
+			tmb, ctx := tomb.WithContext(ctx)
 			saver := &saveFail{
 				idx:    repository.NewIndex(),
 				failAt: int32(test.failAt),
 			}
 
-			b := NewBlobSaver(ctx, &tmb, saver, uint(runtime.NumCPU()))
+			b := NewBlobSaver(ctx, tmb, saver, uint(runtime.NumCPU()))
 
 			var results []FutureBlob
 

internal/archiver/file_saver.go

@@ -58,8 +58,7 @@ type FileSaver struct {
 
 	pol chunker.Pol
 
-	ch   chan<- saveFileJob
-	done <-chan struct{}
+	ch chan<- saveFileJob
 
 	CompleteBlob func(filename string, bytes uint64)
 
@@ -80,7 +79,6 @@ func NewFileSaver(ctx context.Context, t *tomb.Tomb, save SaveBlobFn, pol chunke
 		saveFilePool: NewBufferPool(ctx, int(poolSize), chunker.MaxSize),
 		pol:          pol,
 		ch:           ch,
-		done:         t.Dying(),
 
 		CompleteBlob: func(string, uint64) {},
 	}
@@ -113,11 +111,6 @@ func (s *FileSaver) Save(ctx context.Context, snPath string, file fs.File, fi os
 
 	select {
 	case s.ch <- job:
-	case <-s.done:
-		debug.Log("not sending job, FileSaver is done")
-		_ = file.Close()
-		close(ch)
-		return FutureFile{ch: ch}
 	case <-ctx.Done():
 		debug.Log("not sending job, context is cancelled: %v", ctx.Err())
 		_ = file.Close()

internal/archiver/file_saver_test.go

@@ -30,8 +30,8 @@ func createTestFiles(t testing.TB, num int) (files []string, cleanup func()) {
 	return files, cleanup
 }
 
-func startFileSaver(ctx context.Context, t testing.TB) (*FileSaver, *tomb.Tomb) {
-	var tmb tomb.Tomb
+func startFileSaver(ctx context.Context, t testing.TB) (*FileSaver, context.Context, *tomb.Tomb) {
+	tmb, ctx := tomb.WithContext(ctx)
 
 	saveBlob := func(ctx context.Context, tpe restic.BlobType, buf *Buffer) FutureBlob {
 		ch := make(chan saveBlobResponse)
@@ -45,10 +45,10 @@ func startFileSaver(ctx context.Context, t testing.TB) (*FileSaver, *tomb.Tomb)
 		t.Fatal(err)
 	}
 
-	s := NewFileSaver(ctx, &tmb, saveBlob, pol, workers, workers)
+	s := NewFileSaver(ctx, tmb, saveBlob, pol, workers, workers)
 	s.NodeFromFileInfo = restic.NodeFromFileInfo
 
-	return s, &tmb
+	return s, ctx, tmb
 }
 
 func TestFileSaver(t *testing.T) {
@@ -62,7 +62,7 @@ func TestFileSaver(t *testing.T) {
 	completeFn := func(*restic.Node, ItemStats) {}
 
 	testFs := fs.Local{}
-	s, tmb := startFileSaver(ctx, t)
+	s, ctx, tmb := startFileSaver(ctx, t)
 
 	var results []FutureFile
 

internal/archiver/tree_saver.go

@@ -42,8 +42,7 @@ type TreeSaver struct {
 	saveTree func(context.Context, *restic.Tree) (restic.ID, ItemStats, error)
 	errFn    ErrorFunc
 
-	ch   chan<- saveTreeJob
-	done <-chan struct{}
+	ch chan<- saveTreeJob
 }
 
 // NewTreeSaver returns a new tree saver. A worker pool with treeWorkers is
@@ -53,7 +52,6 @@ func NewTreeSaver(ctx context.Context, t *tomb.Tomb, treeWorkers uint, saveTree
 
 	s := &TreeSaver{
 		ch:       ch,
-		done:     t.Dying(),
 		saveTree: saveTree,
 		errFn:    errFn,
 	}
@@ -78,10 +76,6 @@ func (s *TreeSaver) Save(ctx context.Context, snPath string, node *restic.Node,
 	}
 	select {
 	case s.ch <- job:
-	case <-s.done:
-		debug.Log("not saving tree, TreeSaver is done")
-		close(ch)
-		return FutureTree{ch: ch}
 	case <-ctx.Done():
 		debug.Log("not saving tree, context is cancelled")
 		close(ch)

internal/archiver/tree_saver_test.go

@@ -17,7 +17,7 @@ func TestTreeSaver(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
-	var tmb tomb.Tomb
+	tmb, ctx := tomb.WithContext(ctx)
 
 	saveFn := func(context.Context, *restic.Tree) (restic.ID, ItemStats, error) {
 		return restic.NewRandomID(), ItemStats{TreeBlobs: 1, TreeSize: 123}, nil
@@ -27,7 +27,7 @@ func TestTreeSaver(t *testing.T) {
 		return nil
 	}
 
-	b := NewTreeSaver(ctx, &tmb, uint(runtime.NumCPU()), saveFn, errFn)
+	b := NewTreeSaver(ctx, tmb, uint(runtime.NumCPU()), saveFn, errFn)
 
 	var results []FutureTree
 
@@ -71,7 +71,7 @@ func TestTreeSaverError(t *testing.T) {
 			ctx, cancel := context.WithCancel(context.Background())
 			defer cancel()
 
-			var tmb tomb.Tomb
+			tmb, ctx := tomb.WithContext(ctx)
 
 			var num int32
 			saveFn := func(context.Context, *restic.Tree) (restic.ID, ItemStats, error) {
@@ -88,7 +88,7 @@ func TestTreeSaverError(t *testing.T) {
 				return nil
 			}
 
-			b := NewTreeSaver(ctx, &tmb, uint(runtime.NumCPU()), saveFn, errFn)
+			b := NewTreeSaver(ctx, tmb, uint(runtime.NumCPU()), saveFn, errFn)
 
 			var results []FutureTree