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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Matthew Wilcox <willy@infradead.org>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.4 61/85] fuse: dont check refcount after stealing page
Date:   Tue, 29 Sep 2020 13:00:28 +0200
Message-Id: <20200929105931.262811710@linuxfoundation.org>
In-Reply-To: <20200929105928.198942536@linuxfoundation.org>
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From: Miklos Szeredi <mszeredi@redhat.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@infradead.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/fuse/dev.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 8142f6bf3d310..fc265f4b839ae 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -850,7 +850,6 @@ 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