Commit 14ef1fc7 authored Mar 05, 2019 by Matthew Wilcox Committed by Linus Torvalds Mar 05, 2019

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
9cbb4cb2 ("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>

parent 67b8046f

mm/filemap.c

+0 −10

Original line number	Diff line number	Diff line
		@@ -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;