Re: [PATCH] futex: Fix futex lock the wrong page

From: zhangxiaoxu (A)
Date: Tue Jun 11 2019 - 21:56:34 EST

This patch is for stable branch linux-4.4-y.

On 2019/6/12 9:54, ZhangXiaoxu wrote:
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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
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;