From: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Subject: mm/filemap.c: remove redundant test from find_get_pages_contig
After we establish a reference on the page, we check the pointer
continues to be in the correct position in i_pages. Checking
page->index afterwards is unnecessary; if it were to change, then the
pointer to it from the page cache would also move. The check used to
be done before grabbing a reference on the page which was racy (see
9cbb4cb21b19f ("mm: find_get_pages_contig fixlet")), but nobody noticed
that moving the check after grabbing the reference was redundant.
Link: http://lkml.kernel.org/r/20190107200224.13260-1-willy@xxxxxxxxxxxxx
Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 10 ----------
1 file changed, 10 deletions(-)
--- a/mm/filemap.c~mm-remove-redundant-test-from-find_get_pages_contig
+++ a/mm/filemap.c
@@ -1837,16 +1837,6 @@ unsigned find_get_pages_contig(struct ad
if (unlikely(page != xas_reload(&xas)))
goto put_page;
- /*
- * must check mapping and index after taking the ref.
- * otherwise we can get both false positives and false
- * negatives, which is just confusing to the caller.
- */
- if (!page->mapping || page_to_pgoff(page) != xas.xa_index) {
- put_page(page);
- break;
- }
-
pages[ret] = page;
if (++ret == nr_pages)
break;
_
