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backup: Fix possible deadlock of scanner goroutine 

When the backup is interrupted for some reason while the scanner is
still active this could lead to a deadlock. Interruptions are triggered
by canceling the context object used by both the backup progress UI and
the scanner. It is possible that a context is canceled between the
respective check in the scanner and it calling the `ReportTotal` method
of the UI. The latter method sends a message to the UI goroutine.
However, a canceled context will also stop that goroutine, which can
cause the channel send operation to block indefinitely.

This is resolved by adding a `closed` channel which is closed once the
UI goroutine is stopped and serves as an escape hatch for reported UI
updates.

This change covers not just the ReportTotal method but all potentially
affected methods of the progress UI implementation.
This commit is contained in:
Michael Eischer 2020-09-30 15:48:39 +02:00
parent 94136132e3
commit 8d0ba55ecd
3 changed files with 80 additions and 36 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
changelog/unreleased/issue-2834 Normal file
View File

@ -0,0 +1,7 @@
Bugfix: Fix rare cases of backup command hanging forever
We've fixed an issue with the backup progress reporting which could cause
restic to hang forever right before finishing a backup.
https://github.com/restic/restic/issues/2834
https://github.com/restic/restic/pull/2963

54
internal/ui/backup.go
View File

@ -41,6 +41,7 @@ type Backup struct {
errCh chan struct{}
workerCh chan fileWorkerMessage
finished chan struct{}
closed chan struct{}
summary struct {
sync.Mutex
@ -71,6 +72,7 @@ func NewBackup(term *termstatus.Terminal, verbosity uint) *Backup {
errCh: make(chan struct{}),
workerCh: make(chan fileWorkerMessage),
finished: make(chan struct{}),
closed: make(chan struct{}),
}
}
@ -88,6 +90,7 @@ func (b *Backup) Run(ctx context.Context) error {
t := time.NewTicker(time.Second)
defer t.Stop()
defer close(b.closed)
for {
select {
@ -192,20 +195,27 @@ func (b *Backup) ScannerError(item string, fi os.FileInfo, err error) error {
// Error is the error callback function for the archiver, it prints the error and returns nil.
func (b *Backup) Error(item string, fi os.FileInfo, err error) error {
b.E("error: %v\n", err)
b.errCh <- struct{}{}
select {
case b.errCh <- struct{}{}:
case <-b.closed:
}
return nil
}
// StartFile is called when a file is being processed by a worker.
func (b *Backup) StartFile(filename string) {
b.workerCh <- fileWorkerMessage{
filename: filename,
select {
case b.workerCh <- fileWorkerMessage{filename: filename}:
case <-b.closed:
}
}
// CompleteBlob is called for all saved blobs for files.
func (b *Backup) CompleteBlob(filename string, bytes uint64) {
b.processedCh <- counter{Bytes: bytes}
select {
case b.processedCh <- counter{Bytes: bytes}:
case <-b.closed:
}
}
func formatPercent(numerator uint64, denominator uint64) string {
@ -270,22 +280,28 @@ func (b *Backup) CompleteItem(item string, previous, current *restic.Node, s arc
if current == nil {
// error occurred, tell the status display to remove the line
b.workerCh <- fileWorkerMessage{
filename: item,
done: true,
select {
case b.workerCh <- fileWorkerMessage{filename: item, done: true}:
case <-b.closed:
}
return
}
switch current.Type {
case "file":
b.processedCh <- counter{Files: 1}
b.workerCh <- fileWorkerMessage{
filename: item,
done: true,
select {
case b.processedCh <- counter{Files: 1}:
case <-b.closed:
}
select {
case b.workerCh <- fileWorkerMessage{filename: item, done: true}:
case <-b.closed:
}
case "dir":
b.processedCh <- counter{Dirs: 1}
select {
case b.processedCh <- counter{Dirs: 1}:
case <-b.closed:
}
}
if current.Type == "dir" {
@ -310,10 +326,9 @@ func (b *Backup) CompleteItem(item string, previous, current *restic.Node, s arc
}
} else if current.Type == "file" {
b.workerCh <- fileWorkerMessage{
done: true,
filename: item,
select {
case b.workerCh <- fileWorkerMessage{done: true, filename: item}:
case <-b.closed:
}
if previous == nil {
@ -342,7 +357,7 @@ func (b *Backup) CompleteItem(item string, previous, current *restic.Node, s arc
func (b *Backup) ReportTotal(item string, s archiver.ScanStats) {
select {
case b.totalCh <- counter{Files: s.Files, Dirs: s.Dirs, Bytes: s.Bytes}:
case <-b.finished:
case <-b.closed:
}
if item == "" {
@ -357,7 +372,10 @@ func (b *Backup) ReportTotal(item string, s archiver.ScanStats) {
// Finish prints the finishing messages.
func (b *Backup) Finish(snapshotID restic.ID) {
close(b.finished)
select {
case b.finished <- struct{}{}:
case <-b.closed:
}
b.P("\n")
b.P("Files: %5d new, %5d changed, %5d unmodified\n", b.summary.Files.New, b.summary.Files.Changed, b.summary.Files.Unchanged)

55
internal/ui/json/backup.go
View File

@ -42,6 +42,7 @@ type Backup struct {
errCh chan struct{}
workerCh chan fileWorkerMessage
finished chan struct{}
closed chan struct{}
summary struct {
sync.Mutex
@ -72,6 +73,7 @@ func NewBackup(term *termstatus.Terminal, verbosity uint) *Backup {
errCh: make(chan struct{}),
workerCh: make(chan fileWorkerMessage),
finished: make(chan struct{}),
closed: make(chan struct{}),
}
}
@ -103,6 +105,7 @@ func (b *Backup) Run(ctx context.Context) error {
t := time.NewTicker(time.Second)
defer t.Stop()
defer close(b.closed)
for {
select {
@ -200,20 +203,27 @@ func (b *Backup) Error(item string, fi os.FileInfo, err error) error {
During: "archival",
Item: item,
})
b.errCh <- struct{}{}
select {
case b.errCh <- struct{}{}:
case <-b.closed:
}
return nil
}
// StartFile is called when a file is being processed by a worker.
func (b *Backup) StartFile(filename string) {
b.workerCh <- fileWorkerMessage{
filename: filename,
select {
case b.workerCh <- fileWorkerMessage{filename: filename}:
case <-b.closed:
}
}
// CompleteBlob is called for all saved blobs for files.
func (b *Backup) CompleteBlob(filename string, bytes uint64) {
b.processedCh <- counter{Bytes: bytes}
select {
case b.processedCh <- counter{Bytes: bytes}:
case <-b.closed:
}
}
// CompleteItem is the status callback function for the archiver when a
@ -225,9 +235,9 @@ func (b *Backup) CompleteItem(item string, previous, current *restic.Node, s arc
if current == nil {
// error occurred, tell the status display to remove the line
b.workerCh <- fileWorkerMessage{
filename: item,
done: true,
select {
case b.workerCh <- fileWorkerMessage{filename: item, done: true}:
case <-b.closed:
}
return
}
@ -236,13 +246,19 @@ func (b *Backup) CompleteItem(item string, previous, current *restic.Node, s arc
switch current.Type {
case "file":
b.processedCh <- counter{Files: 1}
b.workerCh <- fileWorkerMessage{
filename: item,
done: true,
select {
case b.processedCh <- counter{Files: 1}:
case <-b.closed:
}
select {
case b.workerCh <- fileWorkerMessage{filename: item, done: true}:
case <-b.closed:
}
case "dir":
b.processedCh <- counter{Dirs: 1}
select {
case b.processedCh <- counter{Dirs: 1}:
case <-b.closed:
}
}
if current.Type == "dir" {
@ -291,10 +307,9 @@ func (b *Backup) CompleteItem(item string, previous, current *restic.Node, s arc
}
} else if current.Type == "file" {
b.workerCh <- fileWorkerMessage{
done: true,
filename: item,
select {
case b.workerCh <- fileWorkerMessage{done: true, filename: item}:
case <-b.closed:
}
if previous == nil {
@ -345,7 +360,7 @@ func (b *Backup) CompleteItem(item string, previous, current *restic.Node, s arc
func (b *Backup) ReportTotal(item string, s archiver.ScanStats) {
select {
case b.totalCh <- counter{Files: uint64(s.Files), Dirs: uint64(s.Dirs), Bytes: s.Bytes}:
case <-b.finished:
case <-b.closed:
}
if item == "" {
@ -365,7 +380,11 @@ func (b *Backup) ReportTotal(item string, s archiver.ScanStats) {
// Finish prints the finishing messages.
func (b *Backup) Finish(snapshotID restic.ID) {
close(b.finished)
select {
case b.finished <- struct{}{}:
case <-b.closed:
}
b.print(summaryOutput{
MessageType: "summary",
FilesNew: b.summary.Files.New,