linux-kernel - Re: [PATCH v6 1/2] mm,hwpoison: fix race with hugetlb page allocation

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Date:   Thu, 12 Aug 2021 09:03:04 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     "Luck, Tony" <tony.luck@...el.com>
CC:     Naoya Horiguchi <nao.horiguchi@...il.com>,
        Oscar Salvador <osalvador@...e.de>,
        Muchun Song <songmuchun@...edance.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 1/2] mm,hwpoison: fix race with hugetlb page allocation

On Wed, Aug 11, 2021 at 09:28:13PM -0700, Luck, Tony wrote:
> On Fri, Jun 04, 2021 at 08:36:31AM +0900, Naoya Horiguchi wrote:
> > From: Naoya Horiguchi <naoya.horiguchi@....com>
> > 
> > When hugetlb page fault (under overcommitting situation) and
> > memory_failure() race, VM_BUG_ON_PAGE() is triggered by the following race:
> > 
> >     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)
> > 
> > __get_hwpoison_page() only checks the page refcount before taking an
> > additional one for memory error handling, which is not enough because
> > there's a time window where compound pages have non-zero refcount during
> > hugetlb page initialization.
> > 
> > So make __get_hwpoison_page() check page status a bit more for hugetlb
> > pages with get_hwpoison_huge_page(). Checking hugetlb-specific flags
> > under hugetlb_lock makes sure that the hugetlb page is not transitive.
> > It's notable that another new function, HWPoisonHandlable(), is helpful
> > to prevent a race against other transitive page states (like a generic
> > compound page just before PageHuge becomes true).
> 
> I'm seeing some strange results when doing a simple injection/recovery.
> 
> Current upstream often fails to offline the page with messages like:
> 
> 	"high-order kernel page"
> or
> 	"unknown page"
> 
> Things were working in v5.12. Broken in v5.13.
> 
> Bisect says that:
> 
> 25182f05ffed ("mm,hwpoison: fix race with hugetlb page allocation")
> 
> is the culprit (though it is possible that there is more than one
> issue ... failure symptoms changed a bit during the bisection).

Sorry for the failures. I think that the following patch (and dependencies)
should solve the issue.
https://lore.kernel.org/linux-mm/20210614021212.223326-6-nao.horiguchi@gmail.com/.
I'll submit the update (maybe the patchset will be smaller by feedbacks)
later soon.

Thanks,
Naoya Horiguchi

> 
> This commit doesn't revert automatically from upstream. But it
> does revert from v5.13. Running with this reverted from v5.13
> gives kernel that recovers normally[1] from hundreds of consecutive
> error injections.
> 
> -Tony
> 
> [1] Almost normally. My test catches SIGBUS and prints the virtual
> address from the siginfo_t structure. Sometimes the address is correct
> other times it is NULL.