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Message-ID: <6f70cc26ccc92d099f1080e4c57ab44709bafd68.camel@surriel.com>
Subject: Re: [PATCH v2] mm: clean up hwpoison page cache page in fault path
From:   Rik van Riel <riel@surriel.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-kernel@vger.kernel.org, kernel-team@fb.com,
        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>,
        Naoya Horiguchi <naoya.horiguchi@nec.com>
Date:   Mon, 14 Feb 2022 20:37:26 -0500
In-Reply-To: <20220214152407.67e0d7dd1a532252c9dd203e@linux-foundation.org>
References: <20220212213740.423efcea@imladris.surriel.com>
         <20220214152407.67e0d7dd1a532252c9dd203e@linux-foundation.org>
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On Mon, 2022-02-14 at 15:24 -0800, Andrew Morton wrote:
>=20
> > Subject: [PATCH v2] mm: clean up hwpoison page cache page in fault
> > path
>=20
> At first scan I thought this was a code cleanup.
>=20
> I think I'll do s/clean up/invalidate/.
>=20
OK, that sounds good.

> On Sat, 12 Feb 2022 21:37:40 -0500 Rik van Riel <riel@surriel.com>
> wrote:
>=20
> > Sometimes the page offlining code can leave behind a hwpoisoned
> > clean
> > page cache page.
>=20
> 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.

> > 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.
> >=20
> > 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.
> >=20
> > 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.
>=20
> Is this worth a cc:stable?

Maybe. I don't know how far back this issue goes...

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