swarm/controller: allow cancellation to propagate

Ensure that cancellation of a pull propagates rather than continuing to
container creation. This ensures that the `Prepare` method is properly
re-entrant.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/distribution/errors.go b/distribution/errors.go
index a9a17bd261..1e7630e380 100644
--- a/distribution/errors.go
+++ b/distribution/errors.go
@@ -40,7 +40,11 @@ type fallbackError struct {
 
 // Error renders the FallbackError as a string.
 func (f fallbackError) Error() string {
-	return f.err.Error()
+	return f.Cause().Error()
+}
+
+func (f fallbackError) Cause() error {
+	return f.err
 }
 
 // shouldV2Fallback returns true if this error is a reason to fall back to v1.