linux-kernel - Re: [linux-pm] [GIT PULL] One more power management fix for 2.6.37

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Date:	Thu, 4 Nov 2010 06:04:05 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Dominik Brodowski <linux@...inikbrodowski.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [linux-pm] [GIT PULL] One more power management fix for 2.6.37

On Wednesday, November 03, 2010, Dominik Brodowski wrote:
> > There's apparently an ordering problem with dpm_list_mtx and
> > socket->skt_mutex. Lockdep details appended.
> > 
> > Dominik, Rafael? What's the proper locking order here, and
> > how do we fix this?
> 
> Thanks for noting this; let's see:
> 
> - We add a PCMCIA device holding skt_mutex, therefore we have the ordering
>   (1) skt_mutex -> (2) dpm_list_mtx
> 
> - If we're suspending, dpm_list_mtx is held, but we need to acquire
>   skt_mutex as we modify some data being protected by skt_mutex
>   (1) dpm_list_mtx -> (2) skt_mutex
> 
> Rafael, any idea on how to solve this? How do other subsystems handle such
> an issue? Do they call device_add() with no locks held at all?

They usually do from what I can tell.

Also only a few of them implement the ->suspend_noirq() callback, which is the
one executed under dpm_list_mtx.

What exactly is protected by skt_mutex ?

Rafael

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