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hugetlb, mbind: fall back to default policy if vma is NULL

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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.

Link: http://lkml.kernel.org/r/20180110104712.GR1732@dhcp22.suse.cz
Signed-off-by: Michal Hocko <mhocko@suse.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Michal Hocko
2018-01-31 16:21:03 -08:00
committed by Linus Torvalds
parent ebd6372358
commit 389c8178d0
3 changed files with 7 additions and 6 deletions
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5
mm/hugetlb.c
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@@ -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);