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

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Message-ID: <Yguh5JUGHln/iRJ8@localhost.localdomain>
Date:   Tue, 15 Feb 2022 13:51:48 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     Rik van Riel <riel@...riel.com>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com,
        linux-mm@...ck.org, Miaohe Lin <linmiaohe@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2] mm: clean up hwpoison page cache page in fault path

On Sat, Feb 12, 2022 at 09:37:40PM -0500, Rik van Riel wrote:
> Sometimes the page offlining code can leave behind a hwpoisoned clean
> page cache page. 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.

Hi Rik,

Do you know how that exactly happens? We should not be really leaving
anything behind, and soft-offline (not hard) code works with the premise
of only poisoning a page in case it was contained, so I am wondering
what is going on here.

In-use pagecache pages are migrated away, and the actual page is
contained, and for clean ones, we already do the invalidate_inode_page()
and then contain it in case we succeed.

One scenario I can imagine this can happen is if by the time we call
page_handle_poison(), someone has taken another refcount on the page,
and the put_page() does not really free it, but I am not sure that
can happen.

-- 
Oscar Salvador
SUSE Labs