linux-kernel - [PATCH 1/2] mm: Remove redundant test from find_get_pages

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Message-Id: <20181122213224.12793-2-willy@infradead.org>
Date:   Thu, 22 Nov 2018 13:32:23 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Hugh Dickins <hughd@...gle.com>,
        Matthew Wilcox <willy@...radead.org>
Subject: [PATCH 1/2] mm: 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.  There's no need to check the
page->mapping or page->index afterwards; if those can change after we've
got the reference, they can change after we return the page to the caller.

Signed-off-by: Matthew Wilcox <willy@...radead.org>
---
 mm/filemap.c | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 81adec8ee02cc..538531590ef2d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1776,16 +1776,6 @@ 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;
-- 
2.19.1