splice: fix i_mutex locking in generic_splice_write()

Rearrange locking of i_mutex on destination so it's only held while
buffers are copied with the pipe_to_file() actor, and not while
waiting for more data on the pipe.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

fs/splice.c

@@ -895,17 +895,29 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 	};
 	ssize_t ret;
 
-	WARN_ON(S_ISFIFO(inode->i_mode));
-	mutex_lock_nested(&inode->i_mutex, I_MUTEX_PARENT);
-	ret = file_remove_suid(out);
-	if (likely(!ret)) {
-		if (pipe->inode)
-			mutex_lock_nested(&pipe->inode->i_mutex, I_MUTEX_CHILD);
-		ret = __splice_from_pipe(pipe, &sd, pipe_to_file);
-		if (pipe->inode)
-			mutex_unlock(&pipe->inode->i_mutex);
-	}
-	mutex_unlock(&inode->i_mutex);
+	if (pipe->inode)
+		mutex_lock_nested(&pipe->inode->i_mutex, I_MUTEX_PARENT);
+
+	splice_from_pipe_begin(&sd);
+	do {
+		ret = splice_from_pipe_next(pipe, &sd);
+		if (ret <= 0)
+			break;
+
+		mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
+		ret = file_remove_suid(out);
+		if (!ret)
+			ret = splice_from_pipe_feed(pipe, &sd, pipe_to_file);
+		mutex_unlock(&inode->i_mutex);
+	} while (ret > 0);
+	splice_from_pipe_end(pipe, &sd);
+
+	if (pipe->inode)
+		mutex_unlock(&pipe->inode->i_mutex);
+
+	if (sd.num_spliced)
+		ret = sd.num_spliced;
+
 	if (ret > 0) {
 		unsigned long nr_pages;