btrfs: don't check for uptodate pages in read_extent_buffer_pages

The only place that reads in pages and thus marks them uptodate for
the btree inode is read_extent_buffer_pages.  Which means that either
pages are already uptodate from an old buffer when creating a new
one in alloc_extent_buffer, or they will be updated by ca call
to read_extent_buffer_pages.  This means the checks for uptodate
pages in read_extent_buffer_pages and read_extent_buffer_subpage are
superfluous and can be removed.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -4136,10 +4136,7 @@ static int read_extent_buffer_subpage(struct extent_buffer *eb, int wait,
 			return ret;
 	}
 
-	if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags) ||
-	    PageUptodate(page) ||
-	    btrfs_subpage_test_uptodate(fs_info, page, eb->start, eb->len)) {
-		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
+	if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags)) {
 		unlock_extent(io_tree, eb->start, eb->start + eb->len - 1,
 			      &cached_state);
 		return 0;
@@ -4166,7 +4163,6 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
 	int i;
 	struct page *page;
 	int locked_pages = 0;
-	int all_uptodate = 1;
 	int num_pages;
 
 	if (test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags))
@@ -4201,21 +4197,6 @@ int read_extent_buffer_pages(struct extent_buffer *eb, int wait, int mirror_num,
 		}
 		locked_pages++;
 	}
-	/*
-	 * We need to firstly lock all pages to make sure that
-	 * the uptodate bit of our pages won't be affected by
-	 * clear_extent_buffer_uptodate().
-	 */
-	for (i = 0; i < num_pages; i++) {
-		page = eb->pages[i];
-		if (!PageUptodate(page))
-			all_uptodate = 0;
-	}
-
-	if (all_uptodate) {
-		set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
-		goto unlock_exit;
-	}
 
 	__read_extent_buffer_pages(eb, mirror_num, check);