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From:   ZhangXiaoxu <zhangxiaoxu5@huawei.com>
To:     <tglx@linutronix.de>, <mingo@redhat.com>, <peterz@infradead.org>,
        <dvhart@infradead.org>, <linux-kernel@vger.kernel.org>,
        <zhangxiaoxu5@huawei.com>
Subject: [PATCH] futex: Fix futex lock the wrong page
Date:   Wed, 12 Jun 2019 09:54:25 +0800
Message-ID: <1560304465-68966-1-git-send-email-zhangxiaoxu5@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-kernel-owner@vger.kernel.org
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The upstram commit 65d8fc777f6d ("futex: Remove requirement
for lock_page() in get_futex_key()") use variable 'page' as
the page head, when merge it to stable branch, the variable
`page_head` is page head.

In the stable branch, the variable `page` not means the page
head, when lock the page head, we should lock 'page_head',
rather than 'page'.

It maybe lead a hung task problem.

Signed-off-by: ZhangXiaoxu <zhangxiaoxu5@huawei.com>
Cc: stable@vger.kernel.org
---
 kernel/futex.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index ec9df5b..15d850f 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -593,8 +593,8 @@ again:
 		 * applies. If this is really a shmem page then the page lock
 		 * will prevent unexpected transitions.
 		 */
-		lock_page(page);
-		shmem_swizzled = PageSwapCache(page) || page->mapping;
+		lock_page(page_head);
+		shmem_swizzled = PageSwapCache(page_head) || page_head->mapping;
 		unlock_page(page_head);
 		put_page(page_head);
 
-- 
2.7.4