linux-kernel - Re: [PATCH v8 1/4] fs/proc/kcore: avoid bounce buffer for ktext data

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Message-ID: <ZL4xif/LX6ZhRqtf@MiWiFi-R3L-srv>
Date:   Mon, 24 Jul 2023 16:08:41 +0800
From:   Baoquan He <bhe@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Jiri Olsa <olsajiri@...il.com>,
        Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Liu Shixin <liushixin2@...wei.com>,
        Jens Axboe <axboe@...nel.dk>,
        Alexander Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v8 1/4] fs/proc/kcore: avoid bounce buffer for ktext data

On 07/24/23 at 08:23am, David Hildenbrand wrote:
> Hi,
> 
> > 
> > I met this too when I executed below command to trigger a kcore reading.
> > I wanted to do a simple testing during system running and got this.
> > 
> >    makedumpfile --mem-usage /proc/kcore
> > 
> > Later I tried your above objdump testing, it corrupted system too.
> > 
> 
> What do you mean with "corrupted system too" --  did it not only fail to
> dump the system, but also actually harmed the system?

>From my testing, reading kcore will cause system panic, then reboot. Not
sure if Jiri saw the same phenomenon.

> 
> @Lorenzo do you plan on reproduce + fix, or should we consider reverting
> that change?

When tested on a arm64 system, the reproducution is stable. I will have
a look too to see if I have some finding this week.