linux-kernel - Re: [PATCH] futex: Fix futex lock the wrong page

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Date:   Wed, 12 Jun 2019 09:50:25 +0800
From:   "zhangxiaoxu (A)" <zhangxiaoxu5@...wei.com>
To:     <tglx@...utronix.de>, <mingo@...hat.com>, <peterz@...radead.org>,
        <dvhart@...radead.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH] futex: Fix futex lock the wrong page

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@...wei.com>
> Cc: stable@...r.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);
>   
>