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Subject: Re: [PATCH] xen/gntdev: fix up blockable calls to mn_invl_range_start
To:     Michal Hocko <mhocko@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, xen-devel@lists.xenproject.org,
        LKML <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>
References: <20180823120707.10998-1-mhocko@kernel.org>
From:   Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Message-ID: <07c7ead4-334d-9b25-f588-25e9b46bbea0@i-love.sakura.ne.jp>
Date:   Thu, 23 Aug 2018 22:44:07 +0900
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On 2018/08/23 21:07, Michal Hocko wrote:
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 57390c7666e5..e7d8bb1bee2a 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -519,21 +519,20 @@ static int mn_invl_range_start(struct mmu_notifier *mn,
>  	struct gntdev_grant_map *map;
>  	int ret = 0;
>  
> -	/* TODO do we really need a mutex here? */
>  	if (blockable)
>  		mutex_lock(&priv->lock);
>  	else if (!mutex_trylock(&priv->lock))
>  		return -EAGAIN;
>  
>  	list_for_each_entry(map, &priv->maps, next) {
> -		if (in_range(map, start, end)) {
> +		if (!blockable && in_range(map, start, end)) {

This still looks strange. Prior to 93065ac753e4, in_range() test was
inside unmap_if_in_range(). But this patch removes in_range() test
if blockable == true. That is, unmap_if_in_range() will unconditionally
unmap if blockable == true, which seems to be an unexpected change.

>  			ret = -EAGAIN;
>  			goto out_unlock;
>  		}
>  		unmap_if_in_range(map, start, end);
>  	}