linux-kernel - Re: [PATCH] device: separate all subsys mutexes (was: Re: [BUG] potential deadlock led by cpu

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Message-ID: <20130312161702.GA4159@kroah.com>
Date:	Tue, 12 Mar 2013 09:17:02 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Michal Hocko <mhocko@...e.cz>, Li Zefan <lizefan@...wei.com>,
	LKML <linux-kernel@...r.kernel.org>,
	cgroups <cgroups@...r.kernel.org>, linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Ingo Molnar <mingo@...hat.com>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: [PATCH] device: separate all subsys mutexes (was: Re: [BUG]
 potential deadlock led by cpu_hotplug lock (memcg involved))

On Tue, Mar 12, 2013 at 05:09:38PM +0100, Peter Zijlstra wrote:
> On Tue, 2013-03-12 at 08:43 -0700, Greg Kroah-Hartman wrote:
> > On Tue, Mar 12, 2013 at 04:28:25PM +0100, Peter Zijlstra wrote:
> > > On Tue, 2013-03-12 at 14:05 +0100, Michal Hocko wrote:
> > > > @@ -111,17 +111,17 @@ struct bus_type {
> > > >         struct iommu_ops *iommu_ops;
> > > >  
> > > >         struct subsys_private *p;
> > > > +       struct lock_class_key __key;
> > > >  };
> > > 
> > > Is struct bus_type constrained to static storage or can people go an
> > > allocate this stuff dynamically? If so, this patch is broken.
> > 
> > I don't think anyone is creating this dynamically, it should be static.
> > Why does this matter, does the lockdep code care about where the
> > variable is declared (heap vs. static)?
> 
> Yeah, lockdep needs keys to be in static storage since its data
> structures are append-only. Dynamic stuff would require being able to
> remove everything related to a key so that we can re-purpose it for the
> next allocation etc.

Ah, that makes sense, thanks.

> Lockdep will in fact warn (and disable itself) if you try and feed it
> dynamic addresses, so using it like this will effectively check your
> bus_type static storage 'requirement'.

Ok, then it should be fine.  Michal, care to redo this and resend it?

thanks,

greg k-h
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