linux-kernel - Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Message-ID: <20100603080556.46d2d671@notabene.brown>
Date:	Thu, 3 Jun 2010 08:05:56 +1000
From:	Neil Brown <neilb@...e.de>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul@...p1.linux-foundation.org" <Paul@...p1.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Florian Mickler <florian@...kler.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...e.de>
Subject: Re: [PATCH] - race-free suspend.  Was: Re: [linux-pm] [PATCH 0/8]
 Suspend block api (version 8)

On Wed, 2 Jun 2010 22:41:14 +0200
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Wednesday 02 June 2010, Neil Brown wrote:
> > - Would this fix the "bug"??
> > - and address the issues that suspend-blockers was created to address?
> > - or are the requirements on user-space too onerous?
> 
> In theory wakeup events can also happen after  wait_for_blockers() has returned
> 0 and I guess we should rollback the suspend in such cases.
> 

I naively assumed this was already the case, but on a slightly closer look at
the code it seems not.

Presumably there is some point deep in the suspend code, probably after the
call to sysdev_suspend, where interrupts are disabled and we are about to
actually suspend.  At that point a simple "is a roll-back required" test
could abort the suspend.
Then any driver that handles wake-up events, if it gets and event that (would
normally cause a wakeup) PM_SUSPEND_PREPARE and PM_POST_SUSPEND, could set
the "roll-back is required" flag.

??

NeilBrown
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