linux-kernel - Re: [PATCH] printk/kdb: Redirect printk messages into kdb in any context

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Message-ID: <20200515103308.GD42471@jagdpanzerIV.localdomain>
Date:   Fri, 15 May 2020 19:33:08 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sumit Garg <sumit.garg@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jason Wessel <jason.wessel@...driver.com>,
        Douglas Anderson <dianders@...omium.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        John Ogness <john.ogness@...utronix.de>
Subject: Re: [PATCH] printk/kdb: Redirect printk messages into kdb in any
 context

On (20/05/15 10:50), Petr Mladek wrote:
> kdb is able to stop kernel even in NMI context where printk() is redirected
> to the printk_safe() lockless variant. Move the check and redirect to kdb
> even in this case.

Can I please have some context what problem does this solve?
I can see that vkdb_printf() calls into console drivers:

	for_each_console(c) {
		c->write(c, cp, retlen - (cp - kdb_buffer));
		touch_nmi_watchdog();
	}

Is this guaranteed that we never execute this path from NMI?
If so, can this please be added to the commit message? A more
detailed commit message will help a lot.

	-ss