linux-kernel - [PATCH 4.9 087/121] fuse: dont check refcount after stealing page

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Message-Id: <20200929105934.488374850@linuxfoundation.org>
Date:   Tue, 29 Sep 2020 13:00:31 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 087/121] fuse: dont check refcount after stealing page

From: Miklos Szeredi <mszeredi@...hat.com>

[ Upstream commit 32f98877c57bee6bc27f443a96f49678a2cd6a50 ]

page_count() is unstable.  Unless there has been an RCU grace period
between when the page was removed from the page cache and now, a
speculative reference may exist from the page cache.

Reported-by: Matthew Wilcox <willy@...radead.org>
Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/fuse/dev.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index b99225e117120..f0129c033bd66 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -825,7 +825,6 @@ static int fuse_check_page(struct page *page)
 {
 	if (page_mapcount(page) ||
 	    page->mapping != NULL ||
-	    page_count(page) != 1 ||
 	    (page->flags & PAGE_FLAGS_CHECK_AT_PREP &
 	     ~(1 << PG_locked |
 	       1 << PG_referenced |
-- 
2.25.1