linux-kernel - RE: [PATCH v2] mm: hwpoison: coredump: support recovery from dump_user

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Date:   Mon, 24 Apr 2023 16:17:27 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>, Kefeng Wang <wangkefeng.wang@...wei.com>
CC:     "chu, jane" <jane.chu@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tong Tiangen <tongtiangen@...wei.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: RE: [PATCH v2] mm: hwpoison: coredump: support recovery from
 dump_user_range()

> > This change seems to not related to what you try to fix.
> > Could this break some other workloads like copying from user address?
> > 
> 
> Yes, this move MCE_IN_KERNEL_COPYIN set into next case, both COPY and
> MCE_SAFE type will set MCE_IN_KERNEL_COPYIN, for EX_TYPE_COPY, we don't
> break it.

Should Linux even try to take a core dump for a SIGBUS generated because
the application accessed a poisoned page?

It doesn't seem like it would be useful. Core dumps are for debugging s/w
program errors in applications and libraries. That isn't the case when there
is a poison consumption. The application did nothing wrong.

This patch is still useful though. There may be an undiscovered poison
page in the application. Avoiding a kernel crash when dumping core
is still a good thing.

-Tony