make sure execerror is released on cancellation

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

solver/jobs.go

@@ -659,6 +659,7 @@ func (s *sharedOp) CalcSlowCache(ctx context.Context, index Index, p PreprocessF
 			case <-ctx.Done():
 				if strings.Contains(err.Error(), context.Canceled.Error()) {
 					complete = false
+					releaseError(err)
 					err = errors.Wrap(ctx.Err(), err.Error())
 				}
 			default:
@@ -717,6 +718,7 @@ func (s *sharedOp) CacheMap(ctx context.Context, index int) (resp *cacheMapResp,
 			case <-ctx.Done():
 				if strings.Contains(err.Error(), context.Canceled.Error()) {
 					complete = false
+					releaseError(err)
 					err = errors.Wrap(ctx.Err(), err.Error())
 				}
 			default:
@@ -774,6 +776,7 @@ func (s *sharedOp) Exec(ctx context.Context, inputs []Result) (outputs []Result,
 			case <-ctx.Done():
 				if strings.Contains(err.Error(), context.Canceled.Error()) {
 					complete = false
+					releaseError(err)
 					err = errors.Wrap(ctx.Err(), err.Error())
 				}
 			default:
@@ -911,3 +914,15 @@ func WrapSlowCache(err error, index Index, res Result) error {
 	}
 	return &SlowCacheError{Index: index, Result: res, error: err}
 }
+
+func releaseError(err error) {
+	if err == nil {
+		return
+	}
+	if re, ok := err.(interface {
+		Release() error
+	}); ok {
+		re.Release()
+	}
+	releaseError(errors.Unwrap(err))
+}

solver/llbsolver/bridge.go

@@ -167,6 +167,8 @@ func newResultProxy(b *llbBridge, req frontend.SolveRequest) *resultProxy {
 				rp.errResults = append(rp.errResults, res)
 				return nil
 			})
+			// acquire ownership so ExecError finalizer doesn't attempt to release as well
+			ee.OwnerBorrowed = true
 		}
 		return res, err
 	}

solver/llbsolver/errdefs/exec.go

@@ -1,14 +1,19 @@
 package errdefs
 
 import (
+	"context"
+	"runtime"
+
 	"github.com/moby/buildkit/solver"
+	"github.com/sirupsen/logrus"
 )
 
 // ExecError will be returned when an error is encountered when evaluating an op.
 type ExecError struct {
 	error
-	Inputs []solver.Result
-	Mounts []solver.Result
+	Inputs        []solver.Result
+	Mounts        []solver.Result
+	OwnerBorrowed bool
 }
 
 func (e *ExecError) Unwrap() error {
@@ -35,13 +40,35 @@ func (e *ExecError) EachRef(fn func(solver.Result) error) (err error) {
 	return err
 }
 
+func (e *ExecError) Release() error {
+	if e.OwnerBorrowed {
+		return nil
+	}
+	err := e.EachRef(func(r solver.Result) error {
+		r.Release(context.TODO())
+		return nil
+	})
+	e.OwnerBorrowed = true
+	return err
+}
+
 func WithExecError(err error, inputs, mounts []solver.Result) error {
 	if err == nil {
 		return nil
 	}
-	return &ExecError{
+	ee := &ExecError{
 		error:  err,
 		Inputs: inputs,
 		Mounts: mounts,
 	}
+	runtime.SetFinalizer(ee, func(e *ExecError) {
+		if !e.OwnerBorrowed {
+			e.EachRef(func(r solver.Result) error {
+				logrus.Warn("leaked execError detected and released")
+				r.Release(context.TODO())
+				return nil
+			})
+		}
+	})
+	return ee
 }