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

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Message-ID: <A5ED84D3BB3A384992CBB9C77DEDA4D414A0339D@USINDEM103.corp.hds.com>
Date:	Fri, 30 Nov 2012 22:59:13 +0000
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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


Thank you  for giving me the comment.

> - Makes the logic in this area even more twisty and complex, when
>   what we need to do is to simplify it
> 
> - Reinitialises in-use locks
> 
> - Gives the boolean variable "yes" three states, but didn't rename
>   that variable to something appropriate.

I understand "yes" is odd.
I just wanted to know if an idea reinitializing locks is acceptable.
But now I understand I have to take another approach.

> 
> - Passes yes==2 into s390's unsuspecting bust_spinlocks() implementation.
>

Sorry. I missed the code.
 
> 
> 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

Seiji



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