pkg/cri/server: add timeout to drain exec io

By default, the child processes spawned by exec process will inherit standard
io file descriptors. The shim server creates a pipe as data channel. Both exec
process and its children write data into the write end of the pipe. And the
shim server will read data from the pipe. If the write end is still open, the
shim server will continue to wait for data from pipe.

So, if the exec command is like `bash -c "sleep 365d &"`, the exec process is
bash and quit after create `sleep 365d`. But the `sleep 365d` will hold the
write end of the pipe for a year! It doesn't make senses that CRI plugin
should wait for it.

For this case, we should use timeout to drain exec process's io instead of
waiting for it.

Fixes: #7802

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

pkg/cri/server/container_execsync.go

@@ -37,6 +37,23 @@ import (
 	cioutil "github.com/containerd/containerd/pkg/ioutil"
 )
 
+// defaultDrainExecIOTimeout is used to drain exec io after exec process exits.
+//
+// By default, the child processes spawned by exec process will inherit standard
+// io file descriptors. The shim server creates a pipe as data channel. Both
+// exec process and its children write data into the write end of the pipe.
+// And the shim server will read data from the pipe. If the write end is still
+// open, the shim server will continue to wait for data from pipe.
+//
+// If the exec command is like `bash -c "sleep 365d &"`, the exec process
+// is bash and quit after create `sleep 365d`. But the `sleep 365d` will hold
+// the write end of the pipe for a year! It doesn't make senses that CRI plugin
+// should wait for it.
+//
+// So, CRI plugin uses 15 seconds to drain the exec io and then deletes exec
+// process to stop copy io in shim side.
+const defaultDrainExecIOTimeout = 15 * time.Second
+
 type cappedWriter struct {
 	w      io.WriteCloser
 	remain int
@@ -159,7 +176,7 @@ func (c *criService) execInternal(ctx context.Context, container containerd.Cont
 	defer func() {
 		deferCtx, deferCancel := util.DeferContext()
 		defer deferCancel()
-		if _, err := process.Delete(deferCtx, containerd.WithProcessKill); err != nil {
+		if _, err := process.Delete(deferCtx, containerd.WithProcessKill); err != nil && !errdefs.IsNotFound(err) {
 			log.G(ctx).WithError(err).Errorf("Failed to delete exec process %q for container %q", execID, id)
 		}
 	}()
@@ -206,8 +223,11 @@ func (c *criService) execInternal(ctx context.Context, container containerd.Cont
 		exitRes := <-exitCh
 		log.G(ctx).Debugf("Timeout received while waiting for exec process kill %q code %d and error %v",
 			execID, exitRes.ExitCode(), exitRes.Error())
-		<-attachDone
-		log.G(ctx).Debugf("Stream pipe for exec process %q done", execID)
+
+		if err := drainExecIO(ctx, process, attachDone); err != nil {
+			log.G(ctx).WithError(err).Warnf("failed to drain exec process %q io", execID)
+		}
+
 		return nil, fmt.Errorf("timeout %v exceeded: %w", opts.timeout, execCtx.Err())
 	case exitRes := <-exitCh:
 		code, _, err := exitRes.Result()
@@ -215,8 +235,10 @@ func (c *criService) execInternal(ctx context.Context, container containerd.Cont
 		if err != nil {
 			return nil, fmt.Errorf("failed while waiting for exec %q: %w", execID, err)
 		}
-		<-attachDone
-		log.G(ctx).Debugf("Stream pipe for exec process %q done", execID)
+
+		if err := drainExecIO(ctx, process, attachDone); err != nil {
+			return nil, fmt.Errorf("failed to drain exec process %q io: %w", execID, err)
+		}
 		return &code, nil
 	}
 }
@@ -249,3 +271,26 @@ func (c *criService) execInContainer(ctx context.Context, id string, opts execOp
 
 	return c.execInternal(ctx, cntr.Container, id, opts)
 }
+
+func drainExecIO(ctx context.Context, execProcess containerd.Process, attachDone <-chan struct{}) error {
+	timer := time.NewTimer(defaultDrainExecIOTimeout)
+	defer timer.Stop()
+
+	select {
+	case <-timer.C:
+
+	case <-attachDone:
+		log.G(ctx).Debugf("Stream pipe for exec process %q done", execProcess.ID())
+		return nil
+	}
+
+	log.G(ctx).Debugf("Exec process %q exits but the io is still hold by other processes. Trying to delete exec process to release io", execProcess.ID())
+	_, err := execProcess.Delete(ctx, containerd.WithProcessKill)
+	if err != nil {
+		if !errdefs.IsNotFound(err) {
+			return fmt.Errorf("failed to release exec io by deleting exec process %q: %w",
+				execProcess.ID(), err)
+		}
+	}
+	return fmt.Errorf("failed to drain exec process %q io because io is still hold by other processes", execProcess.ID())
+}