linux-kernel - Re: [PATCH] printk: Print cpu number along with time

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Message-ID: <20140424232916.GD25446@logfs.org>
Date:	Thu, 24 Apr 2014 19:29:16 -0400
From:	Jörn Engel <joern@...fs.org>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	David Rientjes <rientjes@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, akpm@...ux-foundation.org, cxie@...hat.com,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH] printk: Print cpu number along with time

On Fri, 25 April 2014 00:21:20 +0200, Jiri Kosina wrote:
> On Thu, 24 Apr 2014, David Rientjes wrote:
> 
> > > Well, if you have dmesg dump from panic that happens every other year, and 
> > > you have to do post-mortem analysis on it, I am pretty sure you would love 
> > > to be able to figure out how the stack traces would look like without 
> > > inter-CPU interleaving. And I am pretty sure you wouldn't want to 
> > > insert/enable a tracepoint and wait another two years for the bug to 
> > > trigger again.
> > 
> > Sounds like the appropriate fix would be to serialize stack dumping to the 
> > kernel log.
> 
> That's rather difficult, as it can be done both from NMI and non-NMI 
> contexts, and those are very hard to synchronize.

It is also easy to get wrong and cause a panic() that doesn't reboot
but instead gets stuck somewhere.

Plus, you might want similar serialization for other multi-line debug
messages.  Scsi error messages come to mind, but we have many more
examples.

Jörn

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