Re: [PATCH v2] mm: clean up hwpoison page cache page in fault path

From: "HORIGUCHI NAOYA(堀口　直也)" <naoya.horiguchi@nec.com>
To: Rik van Riel <riel@surriel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"kernel-team@fb.com" <kernel-team@fb.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	Miaohe Lin <linmiaohe@huawei.com>, Mel Gorman <mgorman@suse.de>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Matthew Wilcox <willy@infradead.org>,
	Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: Re: [PATCH v2] mm: clean up hwpoison page cache page in fault path
Date: Tue, 15 Feb 2022 05:15:17 +0000	[thread overview]
Message-ID: <20220215051515.GA1918865@hori.linux.bs1.fc.nec.co.jp> (raw)
In-Reply-To: <6f70cc26ccc92d099f1080e4c57ab44709bafd68.camel@surriel.com>

On Mon, Feb 14, 2022 at 08:37:26PM -0500, Rik van Riel wrote:
> On Mon, 2022-02-14 at 15:24 -0800, Andrew Morton wrote:
> > 
> > > Subject: [PATCH v2] mm: clean up hwpoison page cache page in fault
> > > path
> > 
> > At first scan I thought this was a code cleanup.
> > 
> > I think I'll do s/clean up/invalidate/.
> > 
> OK, that sounds good.
> 
> > On Sat, 12 Feb 2022 21:37:40 -0500 Rik van Riel <riel@surriel.com>
> > wrote:
> > 
> > > Sometimes the page offlining code can leave behind a hwpoisoned
> > > clean
> > > page cache page.
> > 
> > Is this correct behaviour?
> 
> It is not desirable, and the soft page offlining code
> tries to invalidate the page, but I don't think overhauling
> the way we lock and refcount page cache pages just to make
> offlining them more reliable would be worthwhile, when we
> already have a branch in the page fault handler to deal with
> these pages, anyway.

I don't have any idea about how this kind of page is left on page
cache after page offlining.  But I agree with the suggested change.

> 
> > > This can lead to programs being killed over and over
> > > and over again as they fault in the hwpoisoned page, get killed,
> > > and
> > > then get re-spawned by whatever wanted to run them.
> > > 
> > > This is particularly embarrassing when the page was offlined due to
> > > having too many corrected memory errors. Now we are killing tasks
> > > due to them trying to access memory that probably isn't even
> > > corrupted.
> > > 
> > > This problem can be avoided by invalidating the page from the page
> > > fault handler, which already has a branch for dealing with these
> > > kinds of pages. With this patch we simply pretend the page fault
> > > was successful if the page was invalidated, return to userspace,
> > > incur another page fault, read in the file from disk (to a new
> > > memory page), and then everything works again.
> > 
> > Is this worth a cc:stable?
> 
> Maybe. I don't know how far back this issue goes...

This issue should be orthogonal with recent changes on hwpoison, and
the base code targetted by this patch is unchanged since 2016 (4.10-rc1),
so this patch is simply applicable to most of the maintained stable trees
(maybe except 4.9.z).

Acked-by: Naoya Horiguchi <naoya.horiguchi@nec.com>

Thanks,
Naoya Horiguchi