metrics/cgroups: handle error on call to cgroup

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

metrics/cgroups/cgroups.go

@@ -75,7 +75,14 @@ func (m *cgroupsMonitor) Monitor(c runtime.Task) error {
 func (m *cgroupsMonitor) Stop(c runtime.Task) error {
 	info := c.Info()
 	t := c.(*linux.Task)
-	m.collector.collect(info.ID, info.Namespace, t.Cgroup(), m.collector.storedMetrics, false, nil)
+
+	cgroup, err := t.Cgroup()
+	if err != nil {
+		log.G(m.context).WithError(err).Warnf("unable to retrieve cgroup on stop")
+	} else {
+		m.collector.collect(info.ID, info.Namespace, cgroup, m.collector.storedMetrics, false, nil)
+	}
+
 	m.collector.Remove(info.ID, info.Namespace)
 	return nil
 }

metrics/cgroups/metrics.go

@@ -8,9 +8,9 @@ import (
 	"sync"
 
 	"github.com/containerd/cgroups"
+	"github.com/containerd/containerd/log"
 	metrics "github.com/docker/go-metrics"
 	"github.com/prometheus/client_golang/prometheus"
-	"github.com/sirupsen/logrus"
 )
 
 var (
@@ -97,9 +97,10 @@ func (c *collector) collect(id, namespace string, cg cgroups.Cgroup, ch chan<- p
 	if wg != nil {
 		defer wg.Done()
 	}
+
 	stats, err := cg.Stat(cgroups.IgnoreNotExist)
 	if err != nil {
-		logrus.WithError(err).Errorf("stat cgroup %s", id)
+		log.L.WithError(err).Errorf("stat cgroup %s", id)
 		return
 	}
 	for _, m := range c.metrics {