linux-kernel - Re: [PATCH] mm/memory-failure: fix race with compound page split/merge

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Message-Id: <20160421164454.3da1afe01cc4f5adb6b9772c@linux-foundation.org>
Date:	Thu, 21 Apr 2016 16:44:54 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH] mm/memory-failure: fix race with compound page
 split/merge

On Mon, 18 Apr 2016 23:15:52 +0000 Naoya Horiguchi <n-horiguchi@...jp.nec.com> wrote:

> # CCed Andrew,

Thanks.

> On Mon, Apr 18, 2016 at 02:43:45PM +0300, Konstantin Khlebnikov wrote:
> > Get_hwpoison_page() must recheck relation between head and tail pages.
> > 
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> 
> Looks good to me. Without this recheck, the race causes kernel to pin
> an irrelevant page, and finally makes kernel crash for refcount mismcach...

Thanks.  I'll add the above (important!) info to the changelog and
cc:stable.

> > -	return get_page_unless_zero(head);
> > +	if (get_page_unless_zero(head)) {
> > +		if (head == compound_head(page))
> > +			return 1;
> > +
> > +		pr_info("MCE: %#lx cannot catch tail\n", page_to_pfn(page));
> 
> Recently Chen Yucong replaced the label "MCE:" with "Memory failure:",
> but the resolution is trivial, I think.

Yup, that patch is in my (large) backlog.  Away at conferences for
seven days, receiving 100 actionable emails per day.  Give me a few
days ;)