[PATCH] vmsplice: restrict stealing a little more

Apply the same rules as the anon pipe pages, only allow stealing
if no one else is using the page.
Signed-off-by: Jens Axboe <axboe@suse.de>

fs/pipe.c

@@ -184,7 +184,7 @@ void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,
 		kunmap(buf->page);
 }
 
-static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
+int generic_pipe_buf_steal(struct pipe_inode_info *pipe,
 			   struct pipe_buffer *buf)
 {
 	struct page *page = buf->page;
@@ -213,7 +213,7 @@ static struct pipe_buf_operations anon_pipe_buf_ops = {
 	.unmap = generic_pipe_buf_unmap,
 	.pin = generic_pipe_buf_pin,
 	.release = anon_pipe_buf_release,
-	.steal = anon_pipe_buf_steal,
+	.steal = generic_pipe_buf_steal,
 	.get = generic_pipe_buf_get,
 };
 

fs/splice.c

@@ -141,7 +141,7 @@ static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
 	if (!(buf->flags & PIPE_BUF_FLAG_GIFT))
 		return 1;
 
-	return 0;
+	return generic_pipe_buf_steal(pipe, buf);
 }
 
 static struct pipe_buf_operations user_page_pipe_buf_ops = {

include/linux/pipe_fs_i.h

@@ -69,6 +69,7 @@ void *generic_pipe_buf_map(struct pipe_inode_info *, struct pipe_buffer *, int);
 void generic_pipe_buf_unmap(struct pipe_inode_info *, struct pipe_buffer *, void *);
 void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
 int generic_pipe_buf_pin(struct pipe_inode_info *, struct pipe_buffer *);
+int generic_pipe_buf_steal(struct pipe_inode_info *, struct pipe_buffer *);
 
 /*
  * splice is tied to pipes as a transport (at least for now), so we'll just