From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752547AbdHOMFY (ORCPT <rfc822;w@1wt.eu>);
        Tue, 15 Aug 2017 08:05:24 -0400
Received: from cloudserver094114.home.net.pl ([79.96.170.134]:60917 "EHLO
        cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK)
        by vger.kernel.org with ESMTP id S1752499AbdHOMFV (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 15 Aug 2017 08:05:21 -0400
From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>, Steven Rostedt <rostedt@goodmis.org>,
        Jan Kara <jack@suse.cz>, Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Eric Biederman <ebiederm@xmission.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>, Pavel Machek <pavel@ucw.cz>,
        Andreas Mohr <andi@lisas.de>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [RFC][PATCHv5 07/13] printk: register syscore notifier
Date: Tue, 15 Aug 2017 13:56:56 +0200
Message-ID: <1616919.1QsxM0VBqp@aspire.rjw.lan>
In-Reply-To: <20170815025625.1977-8-sergey.senozhatsky@gmail.com>
References: <20170815025625.1977-1-sergey.senozhatsky@gmail.com> <20170815025625.1977-8-sergey.senozhatsky@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 7Bit
Content-Type: text/plain; charset="us-ascii"
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tuesday, August 15, 2017 4:56:19 AM CEST Sergey Senozhatsky wrote:
> We need to switch to emergency printk mode in kernel_kexec(). One
> kernel_kexec() branch calls kernel_restart_prepare(), which updates
> `system_state', however, the other one, when user requested to
> ->preserve_context, does not and we are lacking the information
> in printk about kexec being executed. Register a syscore notifier
> so printk will be notified by syscore_suspend().
> 
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
>  kernel/printk/printk.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index d3f149fad85c..b14e35f94596 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -50,6 +50,7 @@
>  #include <linux/sched/task_stack.h>
>  #include <linux/kthread.h>
>  #include <linux/suspend.h>
> +#include <linux/syscore_ops.h>
>  
>  #include <linux/uaccess.h>
>  #include <asm/sections.h>
> @@ -2941,6 +2942,22 @@ static struct notifier_block printk_pm_nb = {
>  	.notifier_call = printk_pm_notify,
>  };
>  
> +static int printk_syscore_suspend(void)
> +{
> +	printk_emergency_begin();
> +	return 0;
> +}

Somebody looking at suspend/resume code paths only will be wondering why
you need this, because we should be in the emergency mode already when
it is called.

It would be good to add a comment about the kexec context here.

> +
> +static void printk_syscore_resume(void)
> +{
> +	printk_emergency_end();
> +}

This will turn the emergency mode off during resume before the notifier
added by the previous patch AFAICS.  Is this intentional?

Thanks,
Rafael