From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S941616AbcJSOUn (ORCPT <rfc822;w@1wt.eu>);
        Wed, 19 Oct 2016 10:20:43 -0400
Received: from bombadil.infradead.org ([198.137.202.9]:60418 "EHLO
        bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S941228AbcJSOUk (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Wed, 19 Oct 2016 10:20:40 -0400
Date: Wed, 19 Oct 2016 14:21:08 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>,
        Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
        Tejun Heo <tj@kernel.org>, Calvin Owens <calvinowens@fb.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mel Gorman <mgorman@techsingularity.net>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] make printk work again
Message-ID: <20161019122108.GN3102@twins.programming.kicks-ass.net>
References: <20161018170830.405990950@infradead.org>
 <20161019114828.GA414@swordfish>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20161019114828.GA414@swordfish>
User-Agent: Mutt/1.5.23.1 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Oct 19, 2016 at 08:48:28PM +0900, Sergey Senozhatsky wrote:
> On (10/18/16 19:08), Peter Zijlstra wrote:
> > This basically fixes printk by evading everything it does.
> > 
> > There's too many problems with printk, from sleeping locks to broken console
> > drivers. Stop using it.
> > 
> > The early_console drivers are the most robust and simple, use those.
> 
> ACK
> 
> Can we also please ban that pre Because it's a bit tricky.emption thing?

Ha, so that's actually quite complicated. The 3rd patch does what is
simple and robust. Doing more gets very tricky real quick.

So actual preemption is disabled per get_cpu()/put_cpu(), and cross-cpu
interleaving is disabled by that 'lock'. But interrupt (and NMI) nesting
are still possible.

It does sporadically happen, but I've not really found it to be a
problem when reading the output.