lock: Moving locking to handler layer. (#3381)

This is implemented so that the issues like in the
following flow don't affect the behavior of operation.

```
GetObjectInfo()
.... --> Time window for mutation (no lock held)
.... --> Time window for mutation (no lock held)
GetObject()
```

This happens when two simultaneous uploads are made
to the same object the object has returned wrong
info to the client.

Another classic example is "CopyObject" API itself
which reads from a source object and copies to
destination object.

Fixes #3370
Fixes #2912

cmd/event-notifier.go

@@ -301,8 +301,14 @@ func eventNotify(event eventData) {
 // structured notification config.
 func loadNotificationConfig(bucket string, objAPI ObjectLayer) (*notificationConfig, error) {
 	// Construct the notification config path.
-	notificationConfigPath := path.Join(bucketConfigPrefix, bucket, bucketNotificationConfig)
-	objInfo, err := objAPI.GetObjectInfo(minioMetaBucket, notificationConfigPath)
+	ncPath := path.Join(bucketConfigPrefix, bucket, bucketNotificationConfig)
+
+	// Acquire a write lock on notification config before modifying.
+	objLock := globalNSMutex.NewNSLock(minioMetaBucket, ncPath)
+	objLock.RLock()
+	defer objLock.RUnlock()
+
+	objInfo, err := objAPI.GetObjectInfo(minioMetaBucket, ncPath)
 	if err != nil {
 		// 'notification.xml' not found return
 		// 'errNoSuchNotifications'.  This is default when no
@@ -315,7 +321,7 @@ func loadNotificationConfig(bucket string, objAPI ObjectLayer) (*notificationCon
 		return nil, err
 	}
 	var buffer bytes.Buffer
-	err = objAPI.GetObject(minioMetaBucket, notificationConfigPath, 0, objInfo.Size, &buffer)
+	err = objAPI.GetObject(minioMetaBucket, ncPath, 0, objInfo.Size, &buffer)
 	if err != nil {
 		// 'notification.xml' not found return
 		// 'errNoSuchNotifications'.  This is default when no
@@ -350,8 +356,14 @@ func loadListenerConfig(bucket string, objAPI ObjectLayer) ([]listenerConfig, er
 	}
 
 	// Construct the notification config path.
-	listenerConfigPath := path.Join(bucketConfigPrefix, bucket, bucketListenerConfig)
-	objInfo, err := objAPI.GetObjectInfo(minioMetaBucket, listenerConfigPath)
+	lcPath := path.Join(bucketConfigPrefix, bucket, bucketListenerConfig)
+
+	// Acquire a write lock on notification config before modifying.
+	objLock := globalNSMutex.NewNSLock(minioMetaBucket, lcPath)
+	objLock.RLock()
+	defer objLock.RUnlock()
+
+	objInfo, err := objAPI.GetObjectInfo(minioMetaBucket, lcPath)
 	if err != nil {
 		// 'listener.json' not found return
 		// 'errNoSuchNotifications'.  This is default when no
@@ -364,7 +376,7 @@ func loadListenerConfig(bucket string, objAPI ObjectLayer) ([]listenerConfig, er
 		return nil, err
 	}
 	var buffer bytes.Buffer
-	err = objAPI.GetObject(minioMetaBucket, listenerConfigPath, 0, objInfo.Size, &buffer)
+	err = objAPI.GetObject(minioMetaBucket, lcPath, 0, objInfo.Size, &buffer)
 	if err != nil {
 		// 'notification.xml' not found return
 		// 'errNoSuchNotifications'.  This is default when no
@@ -399,6 +411,11 @@ func persistNotificationConfig(bucket string, ncfg *notificationConfig, obj Obje
 
 	// build path
 	ncPath := path.Join(bucketConfigPrefix, bucket, bucketNotificationConfig)
+	// Acquire a write lock on notification config before modifying.
+	objLock := globalNSMutex.NewNSLock(minioMetaBucket, ncPath)
+	objLock.Lock()
+	defer objLock.Unlock()
+
 	// write object to path
 	sha256Sum := getSHA256Hash(buf)
 	_, err = obj.PutObject(minioMetaBucket, ncPath, int64(len(buf)), bytes.NewReader(buf), nil, sha256Sum)
@@ -419,6 +436,11 @@ func persistListenerConfig(bucket string, lcfg []listenerConfig, obj ObjectLayer
 
 	// build path
 	lcPath := path.Join(bucketConfigPrefix, bucket, bucketListenerConfig)
+	// Acquire a write lock on notification config before modifying.
+	objLock := globalNSMutex.NewNSLock(minioMetaBucket, lcPath)
+	objLock.Lock()
+	defer objLock.Unlock()
+
 	// write object to path
 	sha256Sum := getSHA256Hash(buf)
 	_, err = obj.PutObject(minioMetaBucket, lcPath, int64(len(buf)), bytes.NewReader(buf), nil, sha256Sum)
@@ -428,12 +450,34 @@ func persistListenerConfig(bucket string, lcfg []listenerConfig, obj ObjectLayer
 	return err
 }
 
+// Removes notification.xml for a given bucket, only used during DeleteBucket.
+func removeNotificationConfig(bucket string, objAPI ObjectLayer) error {
+	// Verify bucket is valid.
+	if !IsValidBucketName(bucket) {
+		return BucketNameInvalid{Bucket: bucket}
+	}
+
+	ncPath := path.Join(bucketConfigPrefix, bucket, bucketNotificationConfig)
+
+	// Acquire a write lock on notification config before modifying.
+	objLock := globalNSMutex.NewNSLock(minioMetaBucket, ncPath)
+	objLock.Lock()
+	err := objAPI.DeleteObject(minioMetaBucket, ncPath)
+	objLock.Unlock()
+	return err
+}
+
 // Remove listener configuration from storage layer. Used when a bucket is deleted.
 func removeListenerConfig(bucket string, objAPI ObjectLayer) error {
 	// make the path
 	lcPath := path.Join(bucketConfigPrefix, bucket, bucketListenerConfig)
-	// remove it
-	return objAPI.DeleteObject(minioMetaBucket, lcPath)
+
+	// Acquire a write lock on notification config before modifying.
+	objLock := globalNSMutex.NewNSLock(minioMetaBucket, lcPath)
+	objLock.Lock()
+	err := objAPI.DeleteObject(minioMetaBucket, lcPath)
+	objLock.Unlock()
+	return err
 }
 
 // Loads both notification and listener config.