linux-kernel - Re: [PATCH 2/2] printk/console: Enhance the check for consoles using init memory

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Date:   Sat, 15 Jul 2017 07:06:26 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.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>,
        "Fabio M. Di Nitto" <fdinitto@...hat.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH 2/2] printk/console: Enhance the check for consoles using
 init memory

On (07/14/17 14:51), Petr Mladek wrote:
[..]
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index f35d3ac3b8c7..1ebe1525ef64 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2659,8 +2659,16 @@ static int __init printk_late_init(void)
>  	int ret;
>  
>  	for_each_console(con) {
> -		if ((con->flags & CON_BOOT) &&
> -		    init_section_intersects(con, sizeof(*con))) {
> +		if (!(con->flags & CON_BOOT))
> +			continue;
> +
> +		/* Check addresses that might be used for enabled consoles. */
> +		if (init_section_intersects(con, sizeof(*con)) ||
> +		    init_section_contains(con->write, 0) ||
> +		    init_section_contains(con->read, 0) ||
> +		    init_section_contains(con->device, 0) ||
> +		    init_section_contains(con->unblank, 0) ||
> +		    init_section_contains(con->data, 0)) {

sort of a problem here is that the next time anyone adds a new ->foo()
callback to struct console, that person also needs to remember to update
printk_late_init().


a completely crazy idea,
can we have a dedicated "console init" section which we will not offload
if we see keep_bootcon?

or... even crazier... disable bootmem offloading (do not offload init
section) at all if we see keep_bootcon? keep_bootcon is a purely debugging
option which people enable when things are bad and unclear, no one should
be using it otherwise, so may be that idea can be a way to go.

thoughts?

	-ss