Merge pull request #1872 from masters-of-cats/better-find-cgroup-mountpoint

Respect container's cgroup path

libcontainer/cgroups/fs/apply_raw.go

@@ -317,7 +317,7 @@ func getCgroupData(c *configs.Cgroup, pid int) (*cgroupData, error) {
 }
 
 func (raw *cgroupData) path(subsystem string) (string, error) {
-	mnt, err := cgroups.FindCgroupMountpoint(subsystem)
+	mnt, err := cgroups.FindCgroupMountpoint(raw.root, subsystem)
 	// If we didn't mount the subsystem, there is no point we make the path.
 	if err != nil {
 		return "", err

libcontainer/cgroups/systemd/apply_systemd.go

@@ -470,7 +470,7 @@ func ExpandSlice(slice string) (string, error) {
 }
 
 func getSubsystemPath(c *configs.Cgroup, subsystem string) (string, error) {
-	mountpoint, err := cgroups.FindCgroupMountpoint(subsystem)
+	mountpoint, err := cgroups.FindCgroupMountpoint(c.Path, subsystem)
 	if err != nil {
 		return "", err
 	}

libcontainer/cgroups/utils.go

@@ -22,31 +22,41 @@ const (
 )
 
 // https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt
-func FindCgroupMountpoint(subsystem string) (string, error) {
-	mnt, _, err := FindCgroupMountpointAndRoot(subsystem)
+func FindCgroupMountpoint(cgroupPath, subsystem string) (string, error) {
+	mnt, _, err := FindCgroupMountpointAndRoot(cgroupPath, subsystem)
 	return mnt, err
 }
 
-func FindCgroupMountpointAndRoot(subsystem string) (string, string, error) {
+func FindCgroupMountpointAndRoot(cgroupPath, subsystem string) (string, string, error) {
 	// We are not using mount.GetMounts() because it's super-inefficient,
 	// parsing it directly sped up x10 times because of not using Sscanf.
 	// It was one of two major performance drawbacks in container start.
 	if !isSubsystemAvailable(subsystem) {
 		return "", "", NewNotFoundError(subsystem)
 	}
+
 	f, err := os.Open("/proc/self/mountinfo")
 	if err != nil {
 		return "", "", err
 	}
 	defer f.Close()
 
-	scanner := bufio.NewScanner(f)
+	return findCgroupMountpointAndRootFromReader(f, cgroupPath, subsystem)
+}
+
+func findCgroupMountpointAndRootFromReader(reader io.Reader, cgroupPath, subsystem string) (string, string, error) {
+	scanner := bufio.NewScanner(reader)
 	for scanner.Scan() {
 		txt := scanner.Text()
-		fields := strings.Split(txt, " ")
-		for _, opt := range strings.Split(fields[len(fields)-1], ",") {
-			if opt == subsystem {
-				return fields[4], fields[3], nil
+		fields := strings.Fields(txt)
+		if len(fields) < 5 {
+			continue
+		}
+		if strings.HasPrefix(fields[4], cgroupPath) {
+			for _, opt := range strings.Split(fields[len(fields)-1], ",") {
+				if opt == subsystem {
+					return fields[4], fields[3], nil
+				}
 			}
 		}
 	}
@@ -257,7 +267,7 @@ func GetInitCgroupPath(subsystem string) (string, error) {
 }
 
 func getCgroupPathHelper(subsystem, cgroup string) (string, error) {
-	mnt, root, err := FindCgroupMountpointAndRoot(subsystem)
+	mnt, root, err := FindCgroupMountpointAndRoot("", subsystem)
 	if err != nil {
 		return "", err
 	}

libcontainer/cgroups/utils_test.go

@@ -372,7 +372,8 @@ func TestIgnoreCgroup2Mount(t *testing.T) {
 	}
 }
 
-const fakeMountInfo = ` 18 24 0:17 / /sys rw,nosuid,nodev,noexec,relatime - sysfs sysfs rw
+func TestGetClosestMountpointAncestor(t *testing.T) {
+	fakeMountInfo := ` 18 24 0:17 / /sys rw,nosuid,nodev,noexec,relatime - sysfs sysfs rw
 100 99 1:31 / /foo/bar rw,relatime - fake fake rw,fake
 100 99 1:31 / /foo/bar/baz2 rw,relatime - fake fake rw,fake
 100 99 1:31 / /foo/bar/baz rw,relatime - fake fake rw,fake
@@ -382,21 +383,39 @@ const fakeMountInfo = ` 18 24 0:17 / /sys rw,nosuid,nodev,noexec,relatime - sysf
 100 99 1:31 / /unrelated rw,relatime - fake fake rw,fake
 100 99 1:31 / / rw,relatime - fake fake rw,fake
 `
-
-func TestGetClosestMountpointAncestor(t *testing.T) {
 	testCases := []struct {
-		input      string
-		mountinfos string
-		output     string
+		input  string
+		output string
 	}{
-		{input: "/foo/bar/baz/a/b/c", mountinfos: fakeMountInfo, output: "/foo/bar/baz"},
-		{input: "/foo/bar/baz", mountinfos: fakeMountInfo, output: "/foo/bar/baz"},
-		{input: "/foo/bar/bazza", mountinfos: fakeMountInfo, output: "/foo/bar/bazza"},
-		{input: "/a/b/c/d", mountinfos: fakeMountInfo, output: "/"},
+		{input: "/foo/bar/baz/a/b/c", output: "/foo/bar/baz"},
+		{input: "/foo/bar/baz", output: "/foo/bar/baz"},
+		{input: "/foo/bar/bazza", output: "/foo/bar/bazza"},
+		{input: "/a/b/c/d", output: "/"},
 	}
 
 	for _, c := range testCases {
-		mountpoint := GetClosestMountpointAncestor(c.input, c.mountinfos)
+		mountpoint := GetClosestMountpointAncestor(c.input, fakeMountInfo)
+		if mountpoint != c.output {
+			t.Errorf("expected %s, got %s", c.output, mountpoint)
+		}
+	}
+}
+
+func TestFindCgroupMountpointAndRoot(t *testing.T) {
+	fakeMountInfo := `
+35 27 0:29 / /foo rw,nosuid,nodev,noexec,relatime shared:18 - cgroup cgroup rw,devices
+35 27 0:29 / /sys/fs/cgroup/devices rw,nosuid,nodev,noexec,relatime shared:18 - cgroup cgroup rw,devices
+`
+	testCases := []struct {
+		cgroupPath string
+		output     string
+	}{
+		{cgroupPath: "/sys/fs", output: "/sys/fs/cgroup/devices"},
+		{cgroupPath: "", output: "/foo"},
+	}
+
+	for _, c := range testCases {
+		mountpoint, _, _ := findCgroupMountpointAndRootFromReader(strings.NewReader(fakeMountInfo), c.cgroupPath, "devices")
 		if mountpoint != c.output {
 			t.Errorf("expected %s, got %s", c.output, mountpoint)
 		}