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Subject: Re: [PATCH] xen/gntdev: fix up blockable calls to mn_invl_range_start
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        xen-devel@lists.xenproject.org,
        LKML <linux-kernel@vger.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>
References: <20180823120707.10998-1-mhocko@kernel.org>
 <07c7ead4-334d-9b25-f588-25e9b46bbea0@i-love.sakura.ne.jp>
 <20180823135151.GM29735@dhcp22.suse.cz>
From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Message-ID: <470950f0-a579-6c74-c5f0-bea635259176@i-love.sakura.ne.jp>
Date:   Thu, 23 Aug 2018 23:20:54 +0900
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On 2018/08/23 22:51, Michal Hocko wrote:
> You are right. I completely forgot I've removed in_range there. Does
> this look any better?
> 
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index e7d8bb1bee2a..30f81004ea63 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -525,14 +525,20 @@ static int mn_invl_range_start(struct mmu_notifier *mn,
>  		return -EAGAIN;
>  
>  	list_for_each_entry(map, &priv->maps, next) {
> -		if (!blockable && in_range(map, start, end)) {
> +		if (in_range(map, start, end)) {
> +			if (blockable)
> +				continue;
> +
>  			ret = -EAGAIN;
>  			goto out_unlock;
>  		}

This still looks strange. in_range() returns false if map->vma == NULL.
But unmap_if_in_range() unconditionally dereferences map->vma->vm_[start|end] .
Suggestion from Boris looks better.

>  		unmap_if_in_range(map, start, end);
>  	}
>  	list_for_each_entry(map, &priv->freeable_maps, next) {
> -		if (!blockable && in_range(map, start, end)) {
> +		if (in_range(map, start, end)) {
> +			if (blockable)
> +				continue;
> +			
>  			ret = -EAGAIN;
>  			goto out_unlock;
>  		}
>