linux-kernel - Re: "mm: fix lazyfree BUG_ON check in try_to_unmap

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Date:   Thu, 9 Mar 2017 09:50:55 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: "mm: fix lazyfree BUG_ON check in try_to_unmap_one()" build error

On Thu 09-03-17 15:02:26, Minchan Kim wrote:
[...]
> >From 38b10e560d066c2cef8f9d028e14008cefdaa3e0 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@...nel.org>
> Date: Thu, 9 Mar 2017 14:58:23 +0900
> Subject: [PATCH] mm: do not use VM_WARN_ON_ONCE as if condition
> 
> Sergey reported VM_WARN_ON_ONCE returns void with !CONFIG_DEBUG_VM
> so we cannot use it as if's condition unlike WARN_ON.

I would swear I've seen WARN_ON_ONCE there when looking at the previous
patch! Btw. could have simply s@VM_@@ 

> This patch fixes it.
> 
> Signed-off-by: Minchan Kim <minchan@...nel.org>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/rmap.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 1d82057144ba..7d24bb93445b 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1413,12 +1413,11 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
>  			 * Store the swap location in the pte.
>  			 * See handle_pte_fault() ...
>  			 */
> -			if (VM_WARN_ON_ONCE(PageSwapBacked(page) !=
> -						PageSwapCache(page))) {
> +			if (unlikely(PageSwapBacked(page) != PageSwapCache(page))) {
> +				WARN_ON_ONCE(1);
>  				ret = SWAP_FAIL;
>  				page_vma_mapped_walk_done(&pvmw);
>  				break;
> -
>  			}
>  
>  			/* MADV_FREE page check */
> -- 
> 2.7.4

-- 
Michal Hocko
SUSE Labs