linux-kernel - Re: [PATCH v5] mm/hwpoison: fix race between hugetlb free/demotion and memory_failure

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Date:   Wed, 23 Mar 2022 07:22:22 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     Yang Shi <shy828301@...il.com>
CC:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] mm/hwpoison: fix race between hugetlb free/demotion
 and memory_failure_hugetlb()

On Tue, Mar 22, 2022 at 02:55:30AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Mon, Mar 21, 2022 at 05:46:48PM -0700, Yang Shi wrote:
> > On Thu, Mar 17, 2022 at 10:16 PM Naoya Horiguchi
> > <naoya.horiguchi@...ux.dev> wrote:
> > >
> > > From: Naoya Horiguchi <naoya.horiguchi@....com>
> > >
> > > There is a race condition between memory_failure_hugetlb() and hugetlb
> > > free/demotion, which causes setting PageHWPoison flag on the wrong page.
> > > The one simple result is that wrong processes can be killed, but another
> > > (more serious) one is that the actual error is left unhandled, so no one
> > > prevents later access to it, and that might lead to more serious results
> > > like consuming corrupted data.
> > >
> > > Think about the below race window:
> > >
> > >   CPU 1                                   CPU 2
> > >   memory_failure_hugetlb
> > >   struct page *head = compound_head(p);
> > >                                           hugetlb page might be freed to
> > >                                           buddy, or even changed to another
> > >                                           compound page.
> > >
> > >   get_hwpoison_page -- page is not what we want now...
> > >
> > > The compound_head is called outside hugetlb_lock, so the head is not
> > > reliable.
> > >
> > > So set PageHWPoison flag after passing prechecks. And to detect
> > > potential violation, this patch also introduces a new action type
> > > MF_MSG_DIFFERENT_PAGE_SIZE.
> > >
> > > Reported-by: Mike Kravetz <mike.kravetz@...cle.com>
> > > Signed-off-by: Naoya Horiguchi <naoya.horiguchi@....com>
> > > Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> > > Cc: <stable@...r.kernel.org>
> ...
> > > @@ -1547,21 +1545,31 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags)
> > >          * If this happens just bail out.
> > >          */
> > >         if (!PageHuge(p) || compound_head(p) != head) {
> > > +               if (TestSetPageHWPoison(p))
> > > +                       already_hwpoisoned = pfn;
> > > +               else
> > > +                       num_poisoned_pages_inc();
> > >                 action_result(pfn, MF_MSG_DIFFERENT_PAGE_SIZE, MF_IGNORED);
> > 
> > The commit log says "this patch also introduces a new action type
> > MF_MSG_DIFFERENT_PAGE_SIZE", but it is not defined in the patch and it
> > is called here. Did I miss something?
> 
> Sorry, you're right.  MF_MSG_DIFFERENT_PAGE_SIZE is defined in the separate
> patch in mmotm, and disappeared when rebasing (not intended).
> I think of rebasing this to mainline again to apply cleanly to -stable,
> expecting it to applied before other recent hwpoison patches.

The mainline kernel now has the depending patches, so maybe rebasing
the patch onto upstream should no longer cleanly applicable.
(This is due to my poor patch management in mmotm, sorry about that...)

As pointed out by Mike, this patch has readability issue so the base code
needs (maybe substantial) cleanup and redesigning around pinning pages.
So I'm inclined to redoing this fix with more cleaner form, not targeting
to stable.

Thanks,
Naoya Horiguchi