linux-kernel - Re: [PATCH] Avoid dead lock of console related locks in panic case

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Message-Id: <20121130152149.6f266216.akpm@linux-foundation.org>
Date:	Fri, 30 Nov 2012 15:21:49 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Seiji Aguchi <seiji.aguchi@....com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"joe@...ches.com" <joe@...ches.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"kay@...y.org" <kay@...y.org>,
	"jim.cromie@...il.com" <jim.cromie@...il.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"sboyd@...eaurora.org" <sboyd@...eaurora.org>,
	"jason.wessel@...driver.com" <jason.wessel@...driver.com>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: Re: [PATCH] Avoid dead lock of console related locks in panic case

On Fri, 30 Nov 2012 22:59:13 +0000
Seiji Aguchi <seiji.aguchi@....com> wrote:

> > 
> > Let's step back a bit.  Please identify with great specificity the code sites which are stopping other CPUs before taking locks which
> > those other CPUs might have been holding.
> > 
> > Then let's see what we can do to fix up the callers, instead of trying to tidy up after they have made this mess.
> 
> OK.
> I will update my patch without adding complexity.
> The logic will be as follows, if I understand your comment correctly.
> 
>  - take console related locks (logbuf_lock, console_sem)
>  - stop other cpus
>  - release those locks

That would be one way around the problem.  It's still a bit messy,
because we'll have to take more and more locks in the future, as we
identify them.

What I actually meant was: can "this" CPU avoid stopping other CPUs so
early?  If we stop the other CPUs when this CPU is ready to stop itself
then there will never be such deadlocks.

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