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@xxxxxxxx>
> 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@xxxxxxxxxx>
> Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> 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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