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 commit
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@infradead.org
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/filemap.c b/mm/filemap.c
index 9f5e323..935fbc2 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1837,16 +1837,6 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
                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;