block_invalidatepage(): only release page if the full page was invali…

…dated

Prior to commit d47992f ("mm: change invalidatepage prototype to
accept length"), an offset of 0 meant that the full page was being
invalidated.  After that commit, we need to instead check the length.

Jan said:
:
: The only possible issue is that try_to_release_page() was called more
: often than necessary.  Otherwise the issue is harmless but still it's good
: to have this fixed.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: d47992f ("mm: change invalidatepage prototype to accept length")
Signed-off-by: Jeff Moyer <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Cc: Lukas Czerner <[email protected]>
Cc: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/buffer.c

@@ -1511,7 +1511,7 @@ void block_invalidatepage(struct page *page, unsigned int offset,
 	 * The get_block cached value has been unconditionally invalidated,
 	 * so real IO is not possible anymore.
 	 */
-	if (offset == 0)
+	if (length == PAGE_SIZE)
 		try_to_release_page(page, 0);
 out:
 	return;