linux-kernel - Re: [PATCH] xen/gntdev: fix up blockable calls to mn_invl_range

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Date:   Thu, 23 Aug 2018 23:20:54 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        xen-devel@...ts.xenproject.org,
        LKML <linux-kernel@...r.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH] xen/gntdev: fix up blockable calls to mn_invl_range_start

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;
>  		}
>