Date: Wed, 3 Feb 2010 15:08:03 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Sebastian Ott <sebott@linux.vnet.ibm.com>,
       linux-pm@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
       Benjamin Herrenschmidt <benh@kernel.crashing.org>,
       KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Subject: Re: [RFC][PATCH] PM: disable nonboot cpus before suspending devices
Message-Id: <20100203150803.5a4b37fe.akpm@linux-foundation.org>
In-Reply-To: <201002032334.37198.rjw@sisk.pl>
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On Wed, 3 Feb 2010 23:34:37 +0100
"Rafael J. Wysocki" <rjw@sisk.pl> wrote:

> On Wednesday 03 February 2010, Andrew Morton wrote:
> > On Wed, 3 Feb 2010 02:44:23 +0100 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> > 
> > > +static inline gfp_t clear_gfp_allowed_mask(gfp_t mask)
> > > +{
> > > +	gfp_t ret = gfp_allowed_mask;
> > > +	gfp_allowed_mask &= ~mask;
> > > +	return ret;
> > > +}
> > 
> > Fair enuf.
> > 
> > Of course, this is all horridly racy/buggy without locking.  Would I be
> > correct in hoping that all the callers happen when the system is in
> > everyone-is-frozen mode?
> 
> As far as I can tell, gfp_allowed_mask is only touched during init apart from
> this.

Well yes - the new interfaces are the problem - they're racy!

> > Perhaps we should add some documentation (or even an assertion) to
> > prevent someone from using these interfaces from within normal code.
> 
> I thought about that, but didn't invent anything smart enough.
> 
> Well, maybe except for a comment like "this must be called with pm_mutex held",
> because that's the only case when it would be really safe.

Is that the locking rule?  My above guess was incorrect?

Maybe slip a

	BUG_ON(!mutex_is_locked(&pm_mutex));

in there?
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