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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/[email protected]
Signed-off-by: Michal Hocko <[email protected]>
Reported-by: Dan Carpenter <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Mike Kravetz <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Michal Hocko 2018-01-31 16:21:03 -08:00 • committed by Linus Torvalds
commit 389c8178d0
3 changed files with 7 additions and 6 deletions
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3
mm/mempolicy.c
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@ -1121,7 +1121,8 @@ static struct page *new_page(struct page *page, unsigned long start, int **x)
}
if (PageHuge(page)) {
return alloc_huge_page_vma(vma, address);
return alloc_huge_page_vma(page_hstate(compound_head(page)),
vma, address);
} else if (thp_migration_supported() && PageTransHuge(page)) {
struct page *thp;