linux-kernel - [PATCH v10 2/7] filemap: check compound_head(page)->mapping in pagecache_get

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Message-ID: <20190801184244.3169074-3-songliubraving@fb.com>
Date:   Thu, 1 Aug 2019 11:42:39 -0700
From:   Song Liu <songliubraving@...com>
To:     <linux-mm@...ck.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <matthew.wilcox@...cle.com>, <kirill.shutemov@...ux.intel.com>,
        <kernel-team@...com>, <william.kucharski@...cle.com>,
        <akpm@...ux-foundation.org>, <hdanton@...a.com>,
        Song Liu <songliubraving@...com>
Subject: [PATCH v10 2/7] filemap: check compound_head(page)->mapping in pagecache_get_page()

Similar to previous patch, pagecache_get_page() avoids race condition
with truncate by checking page->mapping == mapping. This does not work
for compound pages. This patch let it check compound_head(page)->mapping
instead.

Suggested-by: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Song Liu <songliubraving@...com>
---
 mm/filemap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index d0bd9e585c2f..aaee1ef96f6d 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1644,7 +1644,7 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t offset,
 		}
 
 		/* Has the page been truncated? */
-		if (unlikely(page->mapping != mapping)) {
+		if (unlikely(compound_head(page)->mapping != mapping)) {
 			unlock_page(page);
 			put_page(page);
 			goto repeat;
-- 
2.17.1