linux-kernel - Re: NMI watchdog dump does not print on hard lockup

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Message-ID: <20171013091857.4afe8a7a@gandalf.local.home>
Date:   Fri, 13 Oct 2017 09:18:57 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: NMI watchdog dump does not print on hard lockup

On Fri, 13 Oct 2017 13:14:44 +0200
Petr Mladek <pmladek@...e.com> wrote:

> In general, we could either improve detection of situations when
> the entire system is locked. It would be a reason to risk calling
> consoles even in NMI.
> 
> Or we could accept that the "default" printk is not good for all
> situations and allow more special "debugging" modes:
> 
> 	   + Peter's force_early_printk stuff
> 
> 	   + Allow to disable printk_safe and printk_safe_nmi.
> 	     There will be a risk of a deadlock caused by printk.
> 	     But there also will be a chance to see the messages.

Or add the following case: The watchdog triggers, does the print, then
if it triggers again in a certain amount of time, and the print still
hasn't been flushed, the flush happens then.

-- Steve