linux-kernel - Re: Problem with freezable workqueues

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Date:	Wed, 28 Feb 2007 12:43:46 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Srivatsa Vaddagiri <vatsa@...ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	Gautham R Shenoy <ego@...ibm.com>,
	Johannes Berg <johannes@...solutions.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problem with freezable workqueues

On 02/28, Srivatsa Vaddagiri wrote:
>
> On Wed, Feb 28, 2007 at 11:48:59AM +0300, Oleg Nesterov wrote:
> > On 02/28, Srivatsa Vaddagiri wrote:
> > > We can just thaw the worker thread selectively before kthread_stopping
> > > them. This will let us freeze all worker threads (which we want to for
> > > hotplug anyway).
> > 
> > I am not sure this is a good change for 2.6.21.
> 
> So we make that change when merging the freezer-based hotplug patchset?
> 
> > I strongly believe it is better to change XFS so that it doesn't use
> > create_freezeable_workqueue() as Rafael suggested. 
> 
> Ok no issues. But when we enable freezer-based hotplug, we expect all
> non-singlethreaded worker threads to be frozen (for hotplug atleast).

Yes, we already discussed this :) This is btw another indication we
should kill create_freezeable_workqueue() eventually, so it would be
nice to change the only one user not to use it.

> > Besides, freezeable workqueues are buggy anyway in 2.6.21-rc,
> > 
> > 	http://marc.theaimsgroup.com/?l=linux-kernel&m=116855740612755
> >
> > This means that workqueues become non-freezeable after suspend/resume
> > anyway (if I understand disable_nonboot_cpus() correctly).
> 
> Ah ok. When is the above patch expected to be merged?

Oh, I don't know. Note that this particular patch makes little sense if
we change XFS now (because we have no other users), but we can't drop it,
this will break subsequent patches.

Oleg.

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