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

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Message-ID: <20200611072732.GA429@jagdpanzerIV.localdomain>
Date:   Thu, 11 Jun 2020 16:27:32 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Sumit Garg <sumit.garg@...aro.org>,
        Petr Mladek <pmladek@...e.com>,
        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>,
        John Ogness <john.ogness@...utronix.de>
Subject: Re: [PATCH] printk/kdb: Redirect printk messages into kdb in any
 context

On (20/06/10 17:41), Daniel Thompson wrote:
> > Thanks for the link. I'm slightly surprised it took so many years
> > to notice the addition of printk_nmi/printk_safe :)
> 
> Rather by coincidence (at least I think its a coincidence) the problem
> has recently become much more obvious.
> 
> 0d00449c7a28 ("x86: Replace ist_enter() with nmi_enter()") just brought
> this to the surface by treating debug traps as NMIs. This means the CPU
> that takes a breakpoint, and where almost all of the kdb printk() calls
> take place, will now unconditionally have printk() interception enabled.

Interesting. Feels like ist_enter() should have been using
printk_nmi_enter/exit() in the first place.

	-ss