From 4cbef07d37f74ced75c33e2223ff93e6049a3415 Mon Sep 17 00:00:00 2001
From: Preetha Appan <preetha@hashicorp.com>
Date: Fri, 19 Jan 2018 10:09:30 -0600
Subject: [PATCH] Prevent side effect modification of select options when
 preferred nodes are set

---
 scheduler/stack.go      |  7 ++++---
 scheduler/stack_test.go | 11 +++++++++--
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/scheduler/stack.go b/scheduler/stack.go
index 92e65aa04..16a982b7a 100644
--- a/scheduler/stack.go
+++ b/scheduler/stack.go
@@ -172,13 +172,14 @@ func (s *GenericStack) Select(tg *structs.TaskGroup, options *SelectOptions) (*R
 	if options != nil && len(options.PreferredNodes) > 0 {
 		originalNodes := s.source.nodes
 		s.source.SetNodes(options.PreferredNodes)
-		options.PreferredNodes = nil
-		if option, resources := s.Select(tg, options); option != nil {
+		optionsNew := *options
+		optionsNew.PreferredNodes = nil
+		if option, resources := s.Select(tg, &optionsNew); option != nil {
 			s.source.SetNodes(originalNodes)
 			return option, resources
 		}
 		s.source.SetNodes(originalNodes)
-		return s.Select(tg, options)
+		return s.Select(tg, &optionsNew)
 	}
 
 	// Reset the max selector and context
diff --git a/scheduler/stack_test.go b/scheduler/stack_test.go
index b245ac418..cf8084ea8 100644
--- a/scheduler/stack_test.go
+++ b/scheduler/stack_test.go
@@ -8,6 +8,7 @@ import (
 
 	"github.com/hashicorp/nomad/nomad/mock"
 	"github.com/hashicorp/nomad/nomad/structs"
+	"github.com/stretchr/testify/require"
 )
 
 func BenchmarkServiceStack_With_ComputedClass(b *testing.B) {
@@ -140,7 +141,8 @@ func TestServiceStack_Select_PreferringNodes(t *testing.T) {
 
 	// Create a preferred node
 	preferredNode := mock.Node()
-	selectOptions := &SelectOptions{PreferredNodes: []*structs.Node{preferredNode}}
+	prefNodes := []*structs.Node{preferredNode}
+	selectOptions := &SelectOptions{PreferredNodes: prefNodes}
 	option, _ := stack.Select(job.TaskGroups[0], selectOptions)
 	if option == nil {
 		t.Fatalf("missing node %#v", ctx.Metrics())
@@ -149,12 +151,16 @@ func TestServiceStack_Select_PreferringNodes(t *testing.T) {
 		t.Fatalf("expected: %v, actual: %v", option.Node.ID, preferredNode.ID)
 	}
 
+	// Make sure select doesn't have a side effect on preferred nodes
+	require.Equal(t, prefNodes, selectOptions.PreferredNodes)
+
 	// Change the preferred node's kernel to windows and ensure the allocations
 	// are placed elsewhere
 	preferredNode1 := preferredNode.Copy()
 	preferredNode1.Attributes["kernel.name"] = "windows"
 	preferredNode1.ComputeClass()
-	selectOptions = &SelectOptions{PreferredNodes: []*structs.Node{preferredNode1}}
+	prefNodes1 := []*structs.Node{preferredNode1}
+	selectOptions = &SelectOptions{PreferredNodes: prefNodes1}
 	option, _ = stack.Select(job.TaskGroups[0], selectOptions)
 	if option == nil {
 		t.Fatalf("missing node %#v", ctx.Metrics())
@@ -163,6 +169,7 @@ func TestServiceStack_Select_PreferringNodes(t *testing.T) {
 	if option.Node.ID != nodes[0].ID {
 		t.Fatalf("expected: %#v, actual: %#v", nodes[0], option.Node)
 	}
+	require.Equal(t, prefNodes1, selectOptions.PreferredNodes)
 }
 
 func TestServiceStack_Select_MetricsReset(t *testing.T) {