linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Date:	Thu, 27 May 2010 23:16:17 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Paul@...p1.linux-foundation.org,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>, felipe.balbi@...ia.com
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Thu, May 27, 2010 at 10:15 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2010-05-27 at 15:19 -0400, Alan Stern wrote:
>> On Thu, 27 May 2010, Peter Zijlstra wrote:
>>
>> > I still don't see how blocking applications will cause missed wakeups in
>> > anything but a buggy application at worst, and even those will
>> > eventually get the event when they unblock.
>> >
>> > What seems to be the confusion?
>>
>> During forced suspend, applications are block because they are frozen.
>>
>> When an event occurs, the application is notified somehow.  But it
>> can't respond because it is frozen.  Hence the event remains sitting in
>> a kernel queue and the system goes ahead and suspends anyway.  The
>> application doesn't get thawed until the system wakes up at some
>> indefinite time in the future.
>
> If the kernel is awake to put things in queues, we're clearly not
> suspended and userspace is running ?!

Suspend is not an atomic operation. User space is frozen before
freezable kernel threads both of these happen before drivers are
suspended.

-- 
Arve Hjønnevåg
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