linux-kernel - Re: Problem with freezable workqueues

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Message-Id: <200702281941.24698.rjw@sisk.pl>
Date:	Wed, 28 Feb 2007 19:41:23 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	ego@...ibm.com
Cc:	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>, Pavel Machek <pavel@....cz>,
	Johannes Berg <johannes@...solutions.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problem with freezable workqueues

On Wednesday, 28 February 2007 19:17, Gautham R Shenoy wrote:
> On Wed, Feb 28, 2007 at 08:37:26AM +0530, Srivatsa Vaddagiri wrote:
> > 
> > Hmm ..good point. So can we assume that disable/enable_nonboot_cpus() are called
> > with processes frozen already?
> > 
> > Gautham, you need to take this into account in your patchset!
> 
> Yup. That would mean making the freezer reentrant since we will
> be freezing twice (once for suspend and later on for hotplug). This is
> ok since the api in my patches looks like
> freeze_processes(int freeze_event);
> 
> But thaw will be interesting. If we are thawing for hotplug, we gotta
> only thaw processes which were frozen *only* for hotplug.
> 
> Rafael, does that mean more status flags?!

Well, I don't really think so, but we need to store some information in the
freezer (eg. in a status variable).  Namely, we can define a variable, say
tasks_frozen, the value of which will be the bitwise or of the flags
SPE_SUSPEND, SPE_HOTPLUG etc.  In a fully functional system, tasks_frozen
is equal to zero.  If freeze_processes(SPE_SUSPEND) is run, it does
tasks_frozen |= SPE_SUSPEND and analogously for SPE_HOTPLUG etc.
If tasks_frozen is equal to SPE_SUSPEND|SPE_HOTPLUG,  for example, and
thaw_tasks(SPE_HOTPLUG) runs, it only thaws the tasks that need not stay frozen
for the suspend and does tasks_frozen &= ~SPE_SUSPEND etc.

I think something like this should work.

Greetings,
Rafael 
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