2/2 splice: dont readpage

Splice does not need to readpage to bring the page uptodate before writing
to it, because prepare_write will take care of that for us.

Splice is also wrong to SetPageUptodate before the page is actually uptodate.
This results in the old uninitialised memory leak. This gets fixed as a
matter of course when removing the readpage logic.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

fs/splice.c

@@ -593,36 +593,6 @@ static int pipe_to_file(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 			goto out;
 	}
 
-	/*
-	 * We get here with the page locked. If the page is also
-	 * uptodate, we don't need to do more. If it isn't, we
-	 * may need to bring it in if we are not going to overwrite
-	 * the full page.
-	 */
-	if (!PageUptodate(page)) {
-		if (this_len < PAGE_CACHE_SIZE) {
-			ret = mapping->a_ops->readpage(file, page);
-			if (unlikely(ret))
-				goto out;
-
-			lock_page(page);
-
-			if (!PageUptodate(page)) {
-				/*
-				 * Page got invalidated, repeat.
-				 */
-				if (!page->mapping) {
-					unlock_page(page);
-					page_cache_release(page);
-					goto find_page;
-				}
-				ret = -EIO;
-				goto out;
-			}
-		} else
-			SetPageUptodate(page);
-	}
-
 	ret = mapping->a_ops->prepare_write(file, page, offset, offset+this_len);
 	if (unlikely(ret)) {
 		loff_t isize = i_size_read(mapping->host);