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

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Message-ID: <CAMbhsRRsxC0hCKx-Y_pY8z9F9Sbs52fWhCerGvKbt2fH6AWF5Q@mail.gmail.com>
Date:	Thu, 26 Jul 2012 12:51:17 -0700
From:	Colin Cross <ccross@...roid.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
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 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.
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