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repository: fix race condition for blobSaver shutdown

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wg.Go() may not be called after wg.Wait(). This prevents connecting two
errgroups such that the errors are propagated between them if the child
errgroup dynamically starts goroutines. Instead use just a single errgroup,
and sequence the shutdown using a sync.WaitGroup. This is far simpler
and does not require any "clever" tricks.
This commit is contained in:
Michael Eischer
2025-11-24 19:37:51 +01:00
parent 9f87e9096a
commit 5607fd759f
2 changed files with 32 additions and 52 deletions
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55
internal/repository/repository.go
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@@ -42,7 +42,8 @@ type Repository struct {
opts Options
packerWg *errgroup.Group
blobWg *errgroup.Group
mainWg *errgroup.Group
blobSaver *sync.WaitGroup
uploader *packerUploader
treePM *packerManager
dataPM *packerManager
@@ -562,12 +563,14 @@ func (r *Repository) removeUnpacked(ctx context.Context, t restic.FileType, id r
func (r *Repository) WithBlobUploader(ctx context.Context, fn func(ctx context.Context, uploader restic.BlobSaverWithAsync) error) error {
wg, ctx := errgroup.WithContext(ctx)
// pack uploader + wg.Go below + blob saver (CPU bound)
wg.SetLimit(2 + runtime.GOMAXPROCS(0))
r.mainWg = wg
r.startPackUploader(ctx, wg)
saverCtx := r.startBlobSaver(ctx, wg)
// blob saver are spawned on demand, use wait group to keep track of them
r.blobSaver = &sync.WaitGroup{}
wg.Go(func() error {
// must use saverCtx to ensure that the ctx used for saveBlob calls is bound to it
// otherwise the blob saver could deadlock in case of an error.
if err := fn(saverCtx, &blobSaverRepo{repo: r}); err != nil {
if err := fn(ctx, &blobSaverRepo{repo: r}); err != nil {
return err
}
if err := r.flush(ctx); err != nil {
@@ -594,22 +597,6 @@ func (r *Repository) startPackUploader(ctx context.Context, wg *errgroup.Group)
})
}
func (r *Repository) startBlobSaver(ctx context.Context, wg *errgroup.Group) context.Context {
// blob upload computations are CPU bound
blobWg, blobCtx := errgroup.WithContext(ctx)
blobWg.SetLimit(runtime.GOMAXPROCS(0))
r.blobWg = blobWg
wg.Go(func() error {
// As the goroutines are only spawned on demand, wait until the context is canceled.
// This will either happen on an error while saving a blob or when blobWg.Wait() is called
// by flushBlobUploader().
<-blobCtx.Done()
return blobWg.Wait()
})
return blobCtx
}
type blobSaverRepo struct {
repo *Repository
}
@@ -624,28 +611,26 @@ func (r *blobSaverRepo) SaveBlobAsync(ctx context.Context, t restic.BlobType, bu
// Flush saves all remaining packs and the index
func (r *Repository) flush(ctx context.Context) error {
if err := r.flushBlobUploader(); err != nil {
return err
}
r.flushBlobSaver()
r.mainWg = nil
if err := r.flushPacks(ctx); err != nil {
if err := r.flushPackUploader(ctx); err != nil {
return err
}
return r.idx.Flush(ctx, &internalRepository{r})
}
func (r *Repository) flushBlobUploader() error {
if r.blobWg == nil {
return nil
func (r *Repository) flushBlobSaver() {
if r.blobSaver == nil {
return
}
err := r.blobWg.Wait()
r.blobWg = nil
return err
r.blobSaver.Wait()
r.blobSaver = nil
}
// FlushPacks saves all remaining packs.
func (r *Repository) flushPacks(ctx context.Context) error {
func (r *Repository) flushPackUploader(ctx context.Context) error {
if r.packerWg == nil {
return nil
}
@@ -1032,11 +1017,11 @@ func (r *Repository) saveBlob(ctx context.Context, t restic.BlobType, buf []byte
}
func (r *Repository) saveBlobAsync(ctx context.Context, t restic.BlobType, buf []byte, id restic.ID, storeDuplicate bool, cb func(newID restic.ID, known bool, size int, err error)) {
r.blobWg.Go(func() error {
r.mainWg.Go(func() error {
if ctx.Err() != nil {
// fail fast if the context is cancelled
cb(restic.ID{}, false, 0, context.Cause(ctx))
return context.Cause(ctx)
cb(restic.ID{}, false, 0, ctx.Err())
return ctx.Err()
}
newID, known, size, err := r.saveBlob(ctx, t, buf, id, storeDuplicate)
cb(newID, known, size, err)