CSI: no early return when feasibility check fails on eligible nodes

As a performance optimization in the scheduler, feasibility checks
that apply to an entire class are only checked once for all nodes of
that class. Other feasibility checks are "available" checks because
they rely on more ephemeral characteristics and don't contribute to
the hash for the node class. This currently includes only CSI.

We have a separate fast path for "available" checks when the node has
already been marked eligible on the basis of class. This fast path has
a bug where it returns early rather than continuing the loop. This
causes the entire task group to be rejected.

Fix the bug by not returning early in the fast path and instead jump
to the top of the loop like all the other code paths in this method.
Includes a new test exercising topology at whole-scheduler level and a
fix for an existing test that should've caught this previously.

.changelog/13274.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+csi: Fixed a scheduler bug where failed feasibility checks would return early and prevent processing additional nodes
+```

scheduler/feasible.go

@@ -1135,9 +1135,8 @@ OUTER:
 			if w.available(option) {
 				return option
 			}
-			// We match the class but are temporarily unavailable, the eval
-			// should be blocked
-			return nil
+			// We match the class but are temporarily unavailable
+			continue OUTER
 		case EvalComputedClassEscaped:
 			tgEscaped = true
 		case EvalComputedClassUnknown:

scheduler/generic_sched_test.go

@@ -6353,7 +6353,7 @@ func TestServiceSched_CSIVolumesPerAlloc(t *testing.T) {
 	require.NotEqual("", h.Evals[1].BlockedEval,
 		"expected a blocked eval to be spawned")
 	require.Equal(2, h.Evals[1].QueuedAllocations["web"], "expected 2 queued allocs")
-	require.Equal(1, h.Evals[1].FailedTGAllocs["web"].
+	require.Equal(5, h.Evals[1].FailedTGAllocs["web"].
 		ConstraintFiltered["missing CSI Volume volume-unique[3]"])
 
 	// Upsert 2 more per-alloc volumes
@@ -6397,6 +6397,93 @@ func TestServiceSched_CSIVolumesPerAlloc(t *testing.T) {
 
 }
 
+func TestServiceSched_CSITopology(t *testing.T) {
+	ci.Parallel(t)
+	h := NewHarness(t)
+
+	zones := []string{"zone-0", "zone-1", "zone-2", "zone-3"}
+
+	// Create some nodes, each running a CSI plugin with topology for
+	// a different "zone"
+	for i := 0; i < 12; i++ {
+		node := mock.Node()
+		node.Datacenter = zones[i%4]
+		node.CSINodePlugins = map[string]*structs.CSIInfo{
+			"test-plugin-" + zones[i%4]: {
+				PluginID: "test-plugin-" + zones[i%4],
+				Healthy:  true,
+				NodeInfo: &structs.CSINodeInfo{
+					MaxVolumes: 3,
+					AccessibleTopology: &structs.CSITopology{
+						Segments: map[string]string{"zone": zones[i%4]}},
+				},
+			},
+		}
+		require.NoError(t, h.State.UpsertNode(
+			structs.MsgTypeTestSetup, h.NextIndex(), node))
+	}
+
+	// create 2 per-alloc volumes for those zones
+	vol0 := structs.NewCSIVolume("myvolume[0]", 0)
+	vol0.PluginID = "test-plugin-zone-0"
+	vol0.Namespace = structs.DefaultNamespace
+	vol0.AccessMode = structs.CSIVolumeAccessModeSingleNodeWriter
+	vol0.AttachmentMode = structs.CSIVolumeAttachmentModeFilesystem
+	vol0.RequestedTopologies = &structs.CSITopologyRequest{
+		Required: []*structs.CSITopology{{
+			Segments: map[string]string{"zone": "zone-0"},
+		}},
+	}
+
+	vol1 := vol0.Copy()
+	vol1.ID = "myvolume[1]"
+	vol1.PluginID = "test-plugin-zone-1"
+	vol1.RequestedTopologies.Required[0].Segments["zone"] = "zone-1"
+
+	require.NoError(t, h.State.UpsertCSIVolume(
+		h.NextIndex(), []*structs.CSIVolume{vol0, vol1}))
+
+	// Create a job that uses those volumes
+	job := mock.Job()
+	job.Datacenters = zones
+	job.TaskGroups[0].Count = 2
+	job.TaskGroups[0].Volumes = map[string]*structs.VolumeRequest{
+		"myvolume": {
+			Type:     "csi",
+			Name:     "unique",
+			Source:   "myvolume",
+			PerAlloc: true,
+		},
+	}
+
+	require.NoError(t, h.State.UpsertJob(structs.MsgTypeTestSetup, h.NextIndex(), job))
+
+	// Create a mock evaluation to register the job
+	eval := &structs.Evaluation{
+		Namespace:   structs.DefaultNamespace,
+		ID:          uuid.Generate(),
+		Priority:    job.Priority,
+		TriggeredBy: structs.EvalTriggerJobRegister,
+		JobID:       job.ID,
+		Status:      structs.EvalStatusPending,
+	}
+
+	require.NoError(t, h.State.UpsertEvals(structs.MsgTypeTestSetup,
+		h.NextIndex(), []*structs.Evaluation{eval}))
+
+	// Process the evaluation and expect a single plan without annotations
+	err := h.Process(NewServiceScheduler, eval)
+	require.NoError(t, err)
+	require.Len(t, h.Plans, 1, "expected one plan")
+	require.Nil(t, h.Plans[0].Annotations, "expected no annotations")
+
+	// Expect the eval has not spawned a blocked eval
+	require.Equal(t, len(h.CreateEvals), 0)
+	require.Equal(t, "", h.Evals[0].BlockedEval, "did not expect a blocked eval")
+	require.Equal(t, structs.EvalStatusComplete, h.Evals[0].Status)
+
+}
+
 // TestPropagateTaskState asserts that propagateTaskState only copies state
 // when the previous allocation is lost or draining.
 func TestPropagateTaskState(t *testing.T) {