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

Neil Brown
2010-06-02T22:06:17Z

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