linux-kernel - Re: [PATCH 00/10] printk: Avoid deadlock in NMI + vprintk

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Date:	Mon, 1 Jun 2015 15:06:16 +0200
From:	Jan Kara <jack@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Petr Mladek <pmladek@...e.cz>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dave Anderson <anderson@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Kay Sievers <kay@...y.org>, Jiri Kosina <jkosina@...e.cz>,
	Michal Hocko <mhocko@...e.cz>, Jan Kara <jack@...e.cz>,
	linux-kernel@...r.kernel.org, Wang Long <long.wanglong@...wei.com>,
	peifeiyue@...wei.com, dzickus@...hat.com, morgan.wang@...wei.com,
	sasha.levin@...cle.com
Subject: Re: [PATCH 00/10] printk: Avoid deadlock in NMI + vprintk_emit()
 cleanup

On Fri 29-05-15 13:50:45, Andrew Morton wrote:
> On Mon, 25 May 2015 14:46:23 +0200 Petr Mladek <pmladek@...e.cz> wrote:
> 
> > The main source of deadlocks caused by printk() in NMI context has been
> > solved by the commit a9edc88093287 ("x86/nmi: Perform a safe NMI stack
> > trace on all CPUs").
> > 
> > But there are still few warnings printed in the NMI code that could
> > case a deadlock. For example, see the freeze discussed at
> > https://lkml.org/lkml/2015/5/20/481
> 
> I'm not (yet) convinced that we want the entire patchset btw.  Do we
> really want to try to semi-support printk from NMI?  With a rather
> nasty set of hacks?
> 
> Why not just delete the offending printks?
  And what about WARN_ONs and BUG_ONs? Delete as well? Or just don't print
anything when we are in NMI? I agree that NMI is so problematic context
that restricting printk there makes some sence. OTOH propagating
information from NMI to user is useful as well so I'm somewhat undecided.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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