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Date:   Thu, 21 May 2020 15:19:19 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     js1304@...il.com, Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        kernel-team@....com, Vlastimil Babka <vbabka@...e.cz>,
        Christoph Hellwig <hch@...radead.org>,
        Roman Gushchin <guro@...com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Michal Hocko <mhocko@...e.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 06/11] mm/hugetlb: do not modify user provided gfp_mask

On 5/17/20 6:20 PM, js1304@...il.com wrote:
> From: Joonsoo Kim <iamjoonsoo.kim@....com>
> 
> It's not good practice to modify user input. Instead of using it to
> build correct gfp_mask for APIs, this patch introduces another gfp_mask
> field, __gfp_mask, for internal usage.

Modifying the flags as is done in the existing code does not bother me
too much, but that is just my opinion.  Adding __gfp_mask for modifications
is fine with me if others think it is a good thing.

Does dequeue_huge_page_vma() need to be modified so that it will set
ac.__gfp_mask before calling dequeue_huge_page_nodemask()?
-- 
Mike Kravetz

> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> ---
>  mm/hugetlb.c  | 15 ++++++++-------
>  mm/internal.h |  2 ++
>  2 files changed, 10 insertions(+), 7 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 53edd02..5f43b7e 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1069,15 +1069,15 @@ static struct page *dequeue_huge_page_nodemask(struct hstate *h,
>  	struct zoneref *z;
>  	int node = NUMA_NO_NODE;
>  
> -	zonelist = node_zonelist(ac->nid, ac->gfp_mask);
> +	zonelist = node_zonelist(ac->nid, ac->__gfp_mask);
>  
>  retry_cpuset:
>  	cpuset_mems_cookie = read_mems_allowed_begin();
>  	for_each_zone_zonelist_nodemask(zone, z, zonelist,
> -			gfp_zone(ac->gfp_mask), ac->nmask) {
> +			gfp_zone(ac->__gfp_mask), ac->nmask) {
>  		struct page *page;
>  
> -		if (!cpuset_zone_allowed(zone, ac->gfp_mask))
> +		if (!cpuset_zone_allowed(zone, ac->__gfp_mask))
>  			continue;
>  		/*
>  		 * no need to ask again on the same node. Pool is node rather than
> @@ -1952,7 +1952,7 @@ static struct page *alloc_migrate_huge_page(struct hstate *h,
>  	if (hstate_is_gigantic(h))
>  		return NULL;
>  
> -	page = alloc_fresh_huge_page(h, ac->gfp_mask,
> +	page = alloc_fresh_huge_page(h, ac->__gfp_mask,
>  				ac->nid, ac->nmask, NULL);
>  	if (!page)
>  		return NULL;
> @@ -1990,9 +1990,10 @@ struct page *alloc_buddy_huge_page_with_mpol(struct hstate *h,
>  struct page *alloc_huge_page_nodemask(struct hstate *h,
>  				struct alloc_control *ac)
>  {
> -	ac->gfp_mask |= htlb_alloc_mask(h);
> +	ac->__gfp_mask = htlb_alloc_mask(h);
> +	ac->__gfp_mask |= ac->gfp_mask;
>  	if (ac->thisnode && ac->nid != NUMA_NO_NODE)
> -		ac->gfp_mask |= __GFP_THISNODE;
> +		ac->__gfp_mask |= __GFP_THISNODE;
>  
>  	spin_lock(&hugetlb_lock);
>  	if (h->free_huge_pages - h->resv_huge_pages > 0) {
> @@ -2011,7 +2012,7 @@ struct page *alloc_huge_page_nodemask(struct hstate *h,
>  	 * will not come from CMA area
>  	 */
>  	if (ac->skip_cma)
> -		ac->gfp_mask &= ~__GFP_MOVABLE;
> +		ac->__gfp_mask &= ~__GFP_MOVABLE;
>  
>  	return alloc_migrate_huge_page(h, ac);
>  }
> diff --git a/mm/internal.h b/mm/internal.h
> index 6b6507e..3239d71 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -620,6 +620,8 @@ struct alloc_control {
>  	gfp_t gfp_mask;
>  	bool thisnode;
>  	bool skip_cma;
> +
> +	gfp_t __gfp_mask;	/* Used internally in API implementation */
>  };
>  
>  #endif	/* __MM_INTERNAL_H */
> 

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