2019-08-01 23:46:27

by Song Liu

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 <[email protected]>
Signed-off-by: Song Liu <[email protected]>
---
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

2019-08-12 20:34:22

by Johannes Weiner

Subject: Re: [PATCH v10 2/7] filemap: check compound_head(page)->mapping in pagecache_get_page()

On Thu, Aug 01, 2019 at 11:42:39AM -0700, Song Liu wrote:
> 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 <[email protected]>
> Signed-off-by: Song Liu <[email protected]>

Acked-by: Johannes Weiner <[email protected]>