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

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Message-ID: <c5eefc68193669160429437f7151b53f60c1b755.camel@surriel.com>
Date:   Tue, 15 Feb 2022 10:04:57 -0500
From:   Rik van Riel <riel@...riel.com>
To:     Oscar Salvador <osalvador@...e.de>
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 Tue, 2022-02-15 at 13:51 +0100, Oscar Salvador wrote:
> 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.

I do not know the exact failure case, since I have never
caught a system in the act of leaking one of these pages.

I just know I have seen this issue on systems where the
"soft_offline: %#lx: invalidated\n" printk was the only
offline method leaving any message in the kernel log.

However, there are a few code paths through the soft
offlining code path that don't seem to have any printks,
so I am not sure exactly where things went wrong.

I only really found the aftermath, and tested this patch
by loading it as a kernel live patch module on some of
those systems.

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