bugfix: wait for stdin creation before CloseIO

The stdin fifo of exec process is created in containerd side after
client calls Start. If the client calls CloseIO before Start call, the
stdin of exec process is still opened and wait for close.

For this case, client closes stdinCloseSync channel after Start.

Signed-off-by: Wei Fu <fuweid89@gmail.com>

libcontainerd/client_daemon.go

@@ -328,6 +328,13 @@ func (c *client) Start(ctx context.Context, id, checkpointDir string, withStdin
 	return int(t.Pid()), nil
 }
 
+// Exec creates exec process.
+//
+// The containerd client calls Exec to register the exec config in the shim side.
+// When the client calls Start, the shim will create stdin fifo if needs. But
+// for the container main process, the stdin fifo will be created in Create not
+// the Start call. stdinCloseSync channel should be closed after Start exec
+// process.
 func (c *client) Exec(ctx context.Context, containerID, processID string, spec *specs.Process, withStdin bool, attachStdio StdioCallback) (int, error) {
 	ctr := c.getContainer(containerID)
 	if ctr == nil {
@@ -372,7 +379,9 @@ func (c *client) Exec(ctx context.Context, containerID, processID string, spec *
 	ctr.addProcess(processID, p)
 
 	// Signal c.createIO that it can call CloseIO
-	close(stdinCloseSync)
+	//
+	// the stdin of exec process will be created after p.Start in containerd
+	defer close(stdinCloseSync)
 
 	if err = p.Start(ctx); err != nil {
 		p.Delete(context.Background())