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

[zhangxiaoxu (A)]

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;
>   		unlock_page(page_head);
>   		put_page(page_head);
>