Re: [bug report] hugetlb, mempolicy: fix the mbind hugetlb migration

[Michal Hocko <mhocko@suse.com>]

On Wed 10-01-18 11:47:12, Michal Hocko wrote:
> [CC Mike and Naoya]

ping

> From 7227218bd526cceb954a688727d78af0b5874e18 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Wed, 10 Jan 2018 11:40:20 +0100
> Subject: [PATCH] hugetlb, mbind: fall back to default policy if vma is NULL
> 
> Dan Carpenter has noticed that mbind migration callback (new_page)
> can get a NULL vma pointer and choke on it inside alloc_huge_page_vma
> which relies on the VMA to get the hstate. We used to BUG_ON this
> case but the BUG_+ON has been removed recently by "hugetlb, mempolicy:
> fix the mbind hugetlb migration".
> 
> The proper way to handle this is to get the hstate from the migrated
> page and rely on huge_node (resp. get_vma_policy) do the right thing
> with null VMA. We are currently falling back to the default mempolicy in
> that case which is in line what THP path is doing here.
> 
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
>  include/linux/hugetlb.h | 5 +++--
>  mm/hugetlb.c            | 5 ++---
>  mm/mempolicy.c          | 3 ++-
>  3 files changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 612a29b7f6c6..36fa6a2a82e3 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -358,7 +358,8 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
>  struct page *alloc_huge_page_node(struct hstate *h, int nid);
>  struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
>  				nodemask_t *nmask);
> -struct page *alloc_huge_page_vma(struct vm_area_struct *vma, unsigned long address);
> +struct page *alloc_huge_page_vma(struct hstate *h, struct vm_area_struct *vma,
> +				unsigned long address);
>  int huge_add_to_page_cache(struct page *page, struct address_space *mapping,
>  			pgoff_t idx);
>  
> @@ -536,7 +537,7 @@ struct hstate {};
>  #define alloc_huge_page(v, a, r) NULL
>  #define alloc_huge_page_node(h, nid) NULL
>  #define alloc_huge_page_nodemask(h, preferred_nid, nmask) NULL
> -#define alloc_huge_page_vma(vma, address) NULL
> +#define alloc_huge_page_vma(h, vma, address) NULL
>  #define alloc_bootmem_huge_page(h) NULL
>  #define hstate_file(f) NULL
>  #define hstate_sizelog(s) NULL
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index ffcae114ceed..27872270ead7 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1675,16 +1675,15 @@ struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
>  }
>  
>  /* mempolicy aware migration callback */
> -struct page *alloc_huge_page_vma(struct vm_area_struct *vma, unsigned long address)
> +struct page *alloc_huge_page_vma(struct hstate *h, struct vm_area_struct *vma,
> +		unsigned long address)
>  {
>  	struct mempolicy *mpol;
>  	nodemask_t *nodemask;
>  	struct page *page;
> -	struct hstate *h;
>  	gfp_t gfp_mask;
>  	int node;
>  
> -	h = hstate_vma(vma);
>  	gfp_mask = htlb_alloc_mask(h);
>  	node = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
>  	page = alloc_huge_page_nodemask(h, node, nodemask);
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 30e68da64873..a8b7d59002e8 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1097,7 +1097,8 @@ static struct page *new_page(struct page *page, unsigned long start)
>  	}
>  
>  	if (PageHuge(page)) {
> -		return alloc_huge_page_vma(vma, address);
> +		return alloc_huge_page_vma(page_hstate(compound_head(page)),
> +				vma, address);
>  	} else if (PageTransHuge(page)) {
>  		struct page *thp;
>  
> -- 
> 2.15.1
> 
> -- 
> Michal Hocko
> SUSE Labs

-- 
Michal Hocko
SUSE Labs

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