linux-kernel - Re: [PATCH] cpuidle: coupled: fix sleeping while atomic in cpu notifier

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Message-Id: <201207262216.43665.rjw@sisk.pl>
Date:	Thu, 26 Jul 2012 22:16:43 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Colin Cross <ccross@...roid.com>
Cc:	Len Brown <lenb@...nel.org>, Len Brown <len.brown@...el.com>,
	Kevin Hilman <khilman@...com>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	linux-kernel@...r.kernel.org,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] cpuidle: coupled: fix sleeping while atomic in cpu notifier

On Thursday, July 26, 2012, Rafael J. Wysocki wrote:
> On Thursday, July 26, 2012, Colin Cross wrote:
> > On Thu, Jul 26, 2012 at 12:55 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > On Wednesday, July 25, 2012, Colin Cross wrote:
> > >> The cpu hotplug notifier gets called in both atomic and non-atomic
> > >> contexts, it is not always safe to lock a mutex.  Filter out all events
> > >> except the six necessary ones, which are all sleepable, before taking
> > >> the mutex.
> > >
> > > I wonder what mutual exclusion mechanis we rely on when the mutex is not taken?
> > 
> > We don't need any mutual exclusion because the notifier returns immediately.
> 
> Don't we need to disable preemption even?

Sorry, scratch that.  It returns NOTIFY_OK if we're not going to take the
mutex.

Thanks,
Rafael
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