linux-kernel - Re: [PATCH v6] mm/hwpoison: fix race between hugetlb free/demotion and memory_failure

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Message-Id: <20220404185123.5be4389d99a0e4665a775da1@linux-foundation.org>
Date:   Mon, 4 Apr 2022 18:51:23 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     HORIGUCHI NAOYA (堀口　直也) 
        <naoya.horiguchi@....com>
Cc:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Yang Shi <shy828301@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6] mm/hwpoison: fix race between hugetlb free/demotion
 and memory_failure_hugetlb()

On Tue, 5 Apr 2022 01:45:45 +0000 HORIGUCHI NAOYA(堀口　直也) <naoya.horiguchi@....com> wrote:

> On Mon, Apr 04, 2022 at 11:53:33AM -0700, Andrew Morton wrote:
> > On Mon,  4 Apr 2022 18:21:31 +0900 Naoya Horiguchi <naoya.horiguchi@...ux.dev> wrote:
> > 
> > > 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.
> > 
> > Should this fix be backported into stable kernels?
> 
> This is a bug fix, so eligible to send to stable. But I thought that this
> patch is larger than 100 lines (and hard to separeter to finer patches),
> which seems to violate the rule stated in
> Documentation/process/stable-kernel-rules.rst.
> 
> But actually this rule might not be strictly applied (some patches in
> v5.16.y do have more than 100 lines diff...). So if we can ignore this rule
> exceptionally, that's OK and I'll add CC to stable again.

I never actually knew about that rule ;)

Thanks, I added the cc:stable.

> The target commit of Fixed: tag is 761ad8d7c7b5 ("mm: hwpoison: introduce
> memory_failure_hugetlb()") which was introduced in 4.13, so most of active
> stable trees are affected.

Oh. That's good to know.  The original patch didn't have a Fixes: line.
I added that as well.