linux-kernel - Re: [PATCH 0/2] Avoid crashes by early (boot) consoles using init memory

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Message-ID: <20170714143751.GB32632@pathway.suse.cz>
Date:   Fri, 14 Jul 2017 16:37:52 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     "Fabio M. Di Nitto" <fdinitto@...hat.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Matt Redfearn <matt.redfearn@...tec.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH 0/2] Avoid crashes by early (boot) consoles using init
 memory

On Fri 2017-07-14 14:57:45, Fabio M. Di Nitto wrote:
> Hi Petr,
> 
> On 7/14/2017 2:51 PM, Petr Mladek wrote:
> > Some early consoles have code and data in the init section. It makes some
> > sense but this might cause problems when they are not replaced by
> > the real console in time. The two patches fix the safequard and
> > help to avoid the problems.
> > 
> > I though about removing keep_bootcon option completely. But it is useful
> > at least for now.
> 
> Let´s just keep in mind that keep_bootcon was introduced only to debug
> issues (read crashes or hangs) that could happen between disabling
> bootconsole and enabling the real console. It shouldn´t be used for
> anything else really.

This was my initial replay as well. But then I realized that
it was a bad idea to use a freed code and data to debug any other
issue. It would just create crazy issues on its own.

I tried to google 'keep_bootcon'. It found several links to strange
crashes related to this option. Maybe I was not patient enough but
I did not find any page where this option was suggested and helped.

I still think that the option makes some sense but only when
it does not cause more breakages on its own.

> If the new code can replace keep_bootcon, by all mean, go for it :-)

keep_bootcon stays usable for most early consoles. We print a warning
when an unusable console is disabled too early. Also there is a
comment how to fix it.

Best Regards,
Petr