From: ZhangXiaoxu <zhangxiaoxu5@huawei.com>
Date: Wed, 12 Jun 2019 01:54:25 +0000 (+0800)
Subject: futex: Fix futex lock the wrong page
X-Git-Tag: v4.4.183~47
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cd23996afa1441a2b658c33399e644a71025bdd5;p=thirdparty%2Fkernel%2Fstable.git

futex: Fix futex lock the wrong page

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
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/kernel/futex.c b/kernel/futex.c
index ec9df5ba040ba..15d850ffbe29d 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);