@@ -3,6 +3,7 @@ package jsonfilelog

 import (

 	"bytes"

 	"os"

+	"sync"

 	"github.com/docker/docker/daemon/logger"

 	"github.com/docker/docker/pkg/jsonlog"

@@ -12,7 +13,8 @@ import (

 // JSON objects to file

 type JSONFileLogger struct {

 	buf *bytes.Buffer

-	f   *os.File // store for closing

+	f   *os.File   // store for closing

+	mu  sync.Mutex // protects buffer

 }

 // New creates new JSONFileLogger which writes to filename

@@ -29,13 +31,20 @@ func New(filename string) (logger.Logger, error) {

 // Log converts logger.Message to jsonlog.JSONLog and serializes it to file

 func (l *JSONFileLogger) Log(msg *logger.Message) error {

+	l.mu.Lock()

+	defer l.mu.Unlock()

 	err := (&jsonlog.JSONLog{Log: string(msg.Line) + "\n", Stream: msg.Source, Created: msg.Timestamp}).MarshalJSONBuf(l.buf)

 	if err != nil {

 		return err

 	}

 	l.buf.WriteByte('\n')

 	_, err = l.buf.WriteTo(l.f)

-	return err

+	if err != nil {

+		// this buffer is screwed, replace it with another to avoid races

+		l.buf = bytes.NewBuffer(nil)

+		return err

+	}

+	return nil

 }

 // Close closes underlying file