From: Muchun Song <songmuchun@bytedance.com>
To: "HORIGUCHI NAOYA(堀口 直也)" <naoya.horiguchi@nec.com>
Cc: Michal Hocko <mhocko@suse.com>,
"mike.kravetz@oracle.com" <mike.kravetz@oracle.com>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"osalvador@suse.de" <osalvador@suse.de>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [External] Re: [PATCH] mm: hugetlb: fix a race between memory-failure/soft_offline and gather_surplus_pages
Date: Wed, 21 Apr 2021 17:02:44 +0800 [thread overview]
Message-ID: <CAMZfGtXSuuMjtr0zNOxSsN3cYZPAYzuf6bqAVqwoO8q4eQ0HtQ@mail.gmail.com> (raw)
In-Reply-To: <20210421083315.GA7552@hori.linux.bs1.fc.nec.co.jp>
On Wed, Apr 21, 2021 at 4:33 PM HORIGUCHI NAOYA(堀口 直也)
<naoya.horiguchi@nec.com> wrote:
>
> On Wed, Apr 21, 2021 at 10:03:34AM +0200, Michal Hocko wrote:
> > [Cc Naoya]
> >
> > On Wed 21-04-21 14:02:59, Muchun Song wrote:
> > > The possible bad scenario:
> > >
> > > CPU0: CPU1:
> > >
> > > gather_surplus_pages()
> > > page = alloc_surplus_huge_page()
> > > memory_failure_hugetlb()
> > > get_hwpoison_page(page)
> > > __get_hwpoison_page(page)
> > > get_page_unless_zero(page)
> > > zero = put_page_testzero(page)
> > > VM_BUG_ON_PAGE(!zero, page)
> > > enqueue_huge_page(h, page)
> > > put_page(page)
> > >
> > > The refcount can possibly be increased by memory-failure or soft_offline
> > > handlers, we can trigger VM_BUG_ON_PAGE and wrongly add the page to the
> > > hugetlb pool list.
> >
> > The hwpoison side of this looks really suspicious to me. It shouldn't
> > really touch the reference count of hugetlb pages without being very
> > careful (and having hugetlb_lock held).
>
> I have the same feeling, there is a window where a hugepage is refcounted
> during converting from buddy free pages into free hugepage, so refcount
> alone is not enough to prevent the race. hugetlb_lock is retaken after
> alloc_surplus_huge_page returns, so simply holding hugetlb_lock in
> get_hwpoison_page() seems not work. Is there any status bit to show that a
> hugepage is just being initialized (not in free hugepage pool or in use)?
HPageFreed() can indicate whether a page is on the
free pool list.
>
> > What would happen if the
> > reference count was increased after the page has been enqueed into the
> > pool? This can just blow up later.
>
> Yes, this is another concern.
>
> Thanks,
> Naoya Horiguchi
next prev parent reply other threads:[~2021-04-21 9:03 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-21 6:02 [PATCH] mm: hugetlb: fix a race between memory-failure/soft_offline and gather_surplus_pages Muchun Song
2021-04-21 8:03 ` Michal Hocko
2021-04-21 8:15 ` [External] " Muchun Song
2021-04-21 8:21 ` Oscar Salvador
2021-04-21 8:41 ` Muchun Song
2021-04-21 8:49 ` Oscar Salvador
2021-04-21 8:58 ` Muchun Song
2021-04-21 8:43 ` Michal Hocko
2021-04-21 8:25 ` Michal Hocko
2021-04-21 8:33 ` HORIGUCHI NAOYA(堀口 直也)
2021-04-21 9:02 ` Muchun Song [this message]
2021-04-21 18:03 ` Mike Kravetz
2021-04-22 8:27 ` HORIGUCHI NAOYA(堀口 直也)
2021-04-23 8:01 ` HORIGUCHI NAOYA(堀口 直也)
2021-04-28 7:46 ` [PATCH] mm,hwpoison: fix race with compound page allocation Naoya Horiguchi
2021-04-28 8:23 ` Oscar Salvador
2021-04-28 9:18 ` HORIGUCHI NAOYA(堀口 直也)
2021-05-06 1:31 ` [PATCH v2] " Naoya Horiguchi
2021-05-06 8:51 ` Oscar Salvador
2021-05-07 4:17 ` HORIGUCHI NAOYA(堀口 直也)
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