linux-kernel - Re: [PATCH v1] hugetlb: pass head page to remove_hugetlb

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Message-ID: <YK9Wv+EexkCi2+U5@dhcp22.suse.cz>
Date:   Thu, 27 May 2021 10:22:23 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Oscar Salvador <osalvador@...e.de>
Cc:     Naoya Horiguchi <nao.horiguchi@...il.com>, linux-mm@...ck.org,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <songmuchun@...edance.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] hugetlb: pass head page to remove_hugetlb_page()

On Thu 27-05-21 09:47:44, Oscar Salvador wrote:
> On Thu, May 27, 2021 at 08:52:57AM +0900, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@....com>
> > 
> > When memory_failure() or soft_offline_page() is called on a tail page of
> > some hugetlb page, "BUG: unable to handle page fault" error can be
> > triggered.
> > 
> > remove_hugetlb_page() dereferences page->lru, so it's assumed that the
> > page points to a head page, but one of the caller,
> > dissolve_free_huge_page(), provides remove_hugetlb_page() with 'page'
> > which could be a tail page.  So pass 'head' to it, instead.
> > 
> > Fixes: 6eb4e88a6d27 ("hugetlb: create remove_hugetlb_page() to separate functionality")
> > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> 
> Reviewed-by: Oscar Salvador <osalvador@...e.de>
> 
> It is probably worth adding a comment in remove_hugetlb_page() noting
> that we need a head page, so future users do not repeat the same
> mistake.

Ideally this will turn into page folio concept and no comments are
really needed.
-- 
Michal Hocko
SUSE Labs