A sandbox process should wait until it has not been moved into cgroups

PiperOrigin-RevId: 224418900
Change-Id: I53cf4d7c1c70117875b6920f8fd3d58a3b1497e9

runsc/cmd/boot.go

@@ -69,6 +69,9 @@ type Boot struct {
 
 	// userLogFD is the file descriptor to write user logs to.
 	userLogFD int
+
+	// startSyncFD is the file descriptor to synchronize runsc and sandbox.
+	startSyncFD int
 }
 
 // Name implements subcommands.Command.Name.
@@ -99,12 +102,13 @@ func (b *Boot) SetFlags(f *flag.FlagSet) {
 	f.IntVar(&b.cpuNum, "cpu-num", 0, "number of CPUs to create inside the sandbox")
 	f.Uint64Var(&b.totalMem, "total-memory", 0, "sets the initial amount of total memory to report back to the container")
 	f.IntVar(&b.userLogFD, "user-log-fd", 0, "file descriptor to write user logs to. 0 means no logging.")
+	f.IntVar(&b.startSyncFD, "start-sync-fd", -1, "required FD to used to synchronize sandbox startup")
 }
 
 // Execute implements subcommands.Command.Execute.  It starts a sandbox in a
 // waiting state.
 func (b *Boot) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) subcommands.ExitStatus {
-	if b.specFD == -1 || b.controllerFD == -1 || f.NArg() != 1 {
+	if b.specFD == -1 || b.controllerFD == -1 || b.startSyncFD == -1 || f.NArg() != 1 {
 		f.Usage()
 		return subcommands.ExitUsageError
 	}
@@ -155,6 +159,14 @@ func (b *Boot) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 		panic("setCapsAndCallSelf must never return success")
 	}
 
+	// Wait until this process has been moved into cgroups.
+	startSyncFile := os.NewFile(uintptr(b.startSyncFD), "start-sync file")
+	defer startSyncFile.Close()
+	buf := make([]byte, 1)
+	if r, err := startSyncFile.Read(buf); err != nil || r != 1 {
+		Fatalf("Unable to read from the start-sync descriptor: %v", err)
+	}
+
 	// Create the loader.
 	bootArgs := boot.Args{
 		ID:           f.Arg(0),
@@ -173,9 +185,19 @@ func (b *Boot) Execute(_ context.Context, f *flag.FlagSet, args ...interface{})
 	if err != nil {
 		Fatalf("error creating loader: %v", err)
 	}
+
 	// Fatalf exits the process and doesn't run defers. 'l' must be destroyed
 	// explicitly!
 
+	// Notify the parent process the controller has been created.
+	if w, err := startSyncFile.Write(buf); err != nil || w != 1 {
+		l.Destroy()
+		Fatalf("Unable to write into the start-sync descriptor: %v", err)
+	}
+	// startSyncFile is closed here to be sure that starting with this point
+	// the runsc process will not write anything into it.
+	startSyncFile.Close()
+
 	// Notify other processes the loader has been created.
 	l.NotifyLoaderCreated()
 

runsc/sandbox/sandbox.go

@@ -60,7 +60,7 @@ type Sandbox struct {
 	// is running in.
 	Chroot string `json:"chroot"`
 
-	// Ccroup has the cgroup configuration for the sandbox.
+	// Cgroup has the cgroup configuration for the sandbox.
 	Cgroup *cgroup.Cgroup `json:"cgroup"`
 }
 
@@ -69,7 +69,7 @@ type Sandbox struct {
 func Create(id string, spec *specs.Spec, conf *boot.Config, bundleDir, consoleSocket, userLog string, ioFiles []*os.File) (*Sandbox, error) {
 	s := &Sandbox{ID: id}
 	// The Cleanup object cleans up partially created sandboxes when an error occurs.
-	// Any errors occuring during cleanup itself are ignored.
+	// Any errors occurring during cleanup itself are ignored.
 	c := specutils.MakeCleanup(func() { _ = s.destroy() })
 	defer c.Clean()
 
@@ -82,13 +82,25 @@ func Create(id string, spec *specs.Spec, conf *boot.Config, bundleDir, consoleSo
 		}
 	}
 
-	// Create the sandbox process.
-	if err := s.createSandboxProcess(spec, conf, bundleDir, consoleSocket, userLog, ioFiles); err != nil {
-		return nil, err
+	// Create a socket pair to synchronize runsc and sandbox processes.
+	// It is used for the following:
+	// * to notify the sandbox process when it has been moved into cgroups.
+	// * to wait for the controller socket.
+	fds, err := syscall.Socketpair(syscall.AF_UNIX, syscall.SOCK_SEQPACKET, 0)
+	if err != nil {
+		return nil, fmt.Errorf("error creating a start-sync socket pair %q: %v", s.ID, err)
 	}
+	startSyncFile := os.NewFile(uintptr(fds[0]), "start-sync socket")
+	defer startSyncFile.Close()
 
-	// Wait for the control server to come up (or timeout).
-	if err := s.waitForCreated(20 * time.Second); err != nil {
+	sandboxSyncFile := os.NewFile(uintptr(fds[1]), "sandbox start-sync socket")
+
+	// Create the sandbox process.
+	err = s.createSandboxProcess(spec, conf, bundleDir, consoleSocket, userLog, ioFiles, sandboxSyncFile)
+	// sandboxSyncFile has to be closed to be able to detect
+	// when the sandbox process exits unexpectedly.
+	sandboxSyncFile.Close()
+	if err != nil {
 		return nil, err
 	}
 
@@ -98,6 +110,24 @@ func Create(id string, spec *specs.Spec, conf *boot.Config, bundleDir, consoleSo
 		}
 	}
 
+	b := make([]byte, 1)
+	// Notify the sandbox process it has been moved into cgroups.
+	if l, err := startSyncFile.Write(b); err != nil || l != 1 {
+		return nil, fmt.Errorf("error writing into the start-sync descriptor: %v", err)
+	}
+	// Wait until the sandbox process has initialized the controller socket.
+	if l, err := startSyncFile.Read(b); err != nil || l != 1 {
+		return nil, fmt.Errorf("error reading from the start-sync descriptor: %v", err)
+	}
+	// startSyncFile is closed here to be sure that starting with this point
+	// the sandbox process will not write anything into it.
+	startSyncFile.Close()
+
+	// Wait for the control server to come up.
+	if err := s.waitForCreated(); err != nil {
+		return nil, err
+	}
+
 	c.Release()
 	return s, nil
 }
@@ -282,7 +312,7 @@ func (s *Sandbox) connError(err error) error {
 
 // createSandboxProcess starts the sandbox as a subprocess by running the "boot"
 // command, passing in the bundle dir.
-func (s *Sandbox) createSandboxProcess(spec *specs.Spec, conf *boot.Config, bundleDir, consoleSocket, userLog string, ioFiles []*os.File) error {
+func (s *Sandbox) createSandboxProcess(spec *specs.Spec, conf *boot.Config, bundleDir, consoleSocket, userLog string, ioFiles []*os.File, startSyncFile *os.File) error {
 	// nextFD is used to get unused FDs that we can pass to the sandbox.  It
 	// starts at 3 because 0, 1, and 2 are taken by stdin/out/err.
 	nextFD := 3
@@ -346,6 +376,10 @@ func (s *Sandbox) createSandboxProcess(spec *specs.Spec, conf *boot.Config, bund
 	cmd.Args = append(cmd.Args, "--spec-fd="+strconv.Itoa(nextFD))
 	nextFD++
 
+	cmd.ExtraFiles = append(cmd.ExtraFiles, startSyncFile)
+	cmd.Args = append(cmd.Args, "--start-sync-fd="+strconv.Itoa(nextFD))
+	nextFD++
+
 	// If there is a gofer, sends all socket ends to the sandbox.
 	for _, f := range ioFiles {
 		defer f.Close()
@@ -581,21 +615,8 @@ func (s *Sandbox) createSandboxProcess(spec *specs.Spec, conf *boot.Config, bund
 // waitForCreated waits for the sandbox subprocess control server to be
 // running and for the loader to have been created, at which point the sandbox
 // is in Created state.
-func (s *Sandbox) waitForCreated(timeout time.Duration) error {
+func (s *Sandbox) waitForCreated() error {
 	log.Debugf("Waiting for sandbox %q creation", s.ID)
-
-	ready := func() (bool, error) {
-		c, err := client.ConnectTo(boot.ControlSocketAddr(s.ID))
-		if err != nil {
-			return false, nil
-		}
-		// It's alive!
-		c.Close()
-		return true, nil
-	}
-	if err := specutils.WaitForReady(s.Pid, timeout, ready); err != nil {
-		return fmt.Errorf("unexpected error waiting for sandbox %q, err: %v", s.ID, err)
-	}
 	conn, err := s.sandboxConnect()
 	if err != nil {
 		return err