linux-kernel - Re: [PATCH] frontswap: enable call to invalidate area on swapoff

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Message-ID: <20131007153756.GA4473@variantweb.net>
Date:	Mon, 7 Oct 2013 10:37:56 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	linux-kernel@...r.kernel.org, Shaohua Li <shli@...ionio.com>,
	Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH] frontswap: enable call to invalidate area on swapoff

On Mon, Oct 07, 2013 at 05:25:41PM +0200, Krzysztof Kozlowski wrote:
> During swapoff the frontswap_map was NULL-ified before calling
> frontswap_invalidate_area(). However the frontswap_invalidate_area()
> exits early if frontswap_map is NULL. Invalidate was never called during
> swapoff.
> 
> This patch moves frontswap_map_set() in swapoff just after calling
> frontswap_invalidate_area() so outside of locks
> (swap_lock and swap_info_struct->lock). This shouldn't be a problem as
> during swapon the frontswap_map_set() is called also outside of any
> locks.
> 
> Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>

Nice catch!

Reviewed-by: Seth Jennings <sjenning@...ux.vnet.ibm.com>

> ---
>  mm/swapfile.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 3963fc2..3a4896b 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1922,10 +1922,10 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
>  	p->cluster_info = NULL;
>  	p->flags = 0;
>  	frontswap_map = frontswap_map_get(p);
> -	frontswap_map_set(p, NULL);
>  	spin_unlock(&p->lock);
>  	spin_unlock(&swap_lock);
>  	frontswap_invalidate_area(type);
> +	frontswap_map_set(p, NULL);
>  	mutex_unlock(&swapon_mutex);
>  	free_percpu(p->percpu_cluster);
>  	p->percpu_cluster = NULL;
> -- 
> 1.7.9.5
> 
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