Re: [PATCH v6 1/2] mm,hwpoison: fix race with hugetlb page allocation
From: HORIGUCHI NAOYA(堀口 直也)
Date: Thu Aug 12 2021 - 05:03:09 EST
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@xxxxxxx>
> > 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"
> "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.
I'll submit the update (maybe the patchset will be smaller by feedbacks)
> 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 from hundreds of consecutive
> error injections.
>  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.