gcs backend: fix race condition on locking (#1342)

Signed-off-by: Oleksii Prudkyi <Oleksii.Prudkyi@gmail.com>

CHANGELOG.md

@@ -16,6 +16,7 @@ BUG FIXES:
 * `tofu test` now supports accessing module outputs when the module has no resources. ([#1409](https://github.com/opentofu/opentofu/pull/1409))
 * Fixed support for provider functions in tests ([#1603](https://github.com/opentofu/opentofu/pull/1603))
 * Added a better error message on `for_each` block with sensitive value of unsuitable type. ([#1485](https://github.com/opentofu/opentofu/pull/1485))
+* Fix race condition on locking in gcs backend ([#1342](https://github.com/opentofu/opentofu/pull/1342))
 
 ## Previous Releases
 

internal/backend/remote-state/gcs/client.go

@@ -7,6 +7,7 @@ package gcs
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"strconv"
@@ -135,9 +136,13 @@ func (c *remoteClient) lockError(err error) *statemgr.LockError {
 	}
 
 	info, infoErr := c.lockInfo()
-	if infoErr != nil {
+	switch {
+	case errors.Is(infoErr, storage.ErrObjectNotExist):
+		// Race condition - file exists initially but then has been deleted by other process
+		lockErr.InconsistentRead = true
+	case infoErr != nil:
 		lockErr.Err = multierror.Append(lockErr.Err, infoErr)
-	} else {
+	default:
 		lockErr.Info = info
 	}
 	return lockErr

internal/states/statemgr/locker.go

@@ -89,9 +89,7 @@ func LockWithContext(ctx context.Context, s Locker, info *LockInfo) (string, err
 			return "", err
 		}
 
-		if le == nil || le.Info == nil || le.Info.ID == "" {
+		if !le.Retriable() {
-			// If we don't have a complete LockError then there's something
-			// wrong with the lock.
 			return "", err
 		}
 
@@ -99,6 +97,11 @@ func LockWithContext(ctx context.Context, s Locker, info *LockInfo) (string, err
 			postLockHook()
 		}
 
+		// Lock() can be repeated without sleep
+		if le.RetriableWithoutDelay() {
+			continue
+		}
+
 		// there's an existing lock, wait and try again
 		select {
 		case <-ctx.Done():
@@ -214,6 +217,10 @@ func (l *LockInfo) String() string {
 type LockError struct {
 	Info *LockInfo
 	Err  error
+
+	// Set when writing of lock file fails because of conflict and
+	// then reading fails because file doesn't exist (removed by other process)
+	InconsistentRead bool
 }
 
 func (e *LockError) Error() string {
@@ -227,3 +234,19 @@ func (e *LockError) Error() string {
 	}
 	return strings.Join(out, "\n")
 }
+
+// Retriable returns true when locking should be retried
+func (e *LockError) Retriable() bool {
+	// If we don't have a complete LockError then there's something
+	// wrong with the lock.
+	if e == nil {
+		return false
+	}
+
+	return e.InconsistentRead || (e.Info != nil && e.Info.ID != "")
+}
+
+// RetriableWithoutDelay returns true when delaying can be avoided
+func (e *LockError) RetriableWithoutDelay() bool {
+	return e != nil && e.InconsistentRead
+}