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

[Michal Hocko <mhocko@suse.com>]

On Wed 17-01-18 23:15:03, Naoya Horiguchi wrote:
> On 01/17/2018 09:18 PM, Michal Hocko wrote:
> > 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.
> 
> vma is used only for getting mempolicy in alloc_huge_page_vma(), so
> falling back to default mempolicy looks better to me than BUG_ON.
> 
> Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

Thanks for the review Naoya!
-- 
Michal Hocko
SUSE Labs

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