linux-kernel - Re: [RFC PATCH(Experimental) 2/4] Revert changes to workqueue.c

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Message-ID: <20070220200936.GB85@tv-sign.ru>
Date:	Tue, 20 Feb 2007 23:09:36 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Srivatsa Vaddagiri <vatsa@...ibm.com>
Cc:	Gautham R Shenoy <ego@...ibm.com>, akpm@...l.org,
	paulmck@...ibm.com, mingo@...e.hu, dipankar@...ibm.com,
	venkatesh.pallipadi@...el.com, linux-kernel@...r.kernel.org,
	rjw@...k.pl
Subject: Re: [RFC PATCH(Experimental) 2/4] Revert changes to workqueue.c

On 02/20, Srivatsa Vaddagiri wrote:
>
> On Sun, Feb 18, 2007 at 12:59:28AM +0300, Oleg Nesterov wrote:
> > Before you begin. You are doing CPU_DOWN_PREPARE after freeze_processes().
> > Not good. This makes impossible to do flush_workueue() at CPU_DOWN_PREPARE
> > stage, we have callers.
> 
> We have few solutions to deal with this:
> 
> a. Mark such workqueues not freezable for hotplug
> b. If above is not possible, don't call flush_workqueue in DOWN_PREPARE
> c. If above is not possible, send DOWN_PREPARE before freeze_processes()
> 
> I would prefer a solution in the above order listed.
> 
> Which caller are you referring to here? Maybe we can decide on the
> option after we see the users of flush_workqueue() in DOWN_PREPARE.

mm/slab.c:cpuup_callback()

> > I'm afraid it won't be so easy to solve all locking/racing problems. Will
> > wait for the patch :)
> 
> I dont see problems for workqueue.c even if we follow option c. Do you
> see any?

I don't right now... Oh, I already forgot everything :) I'll try to recall
when I see the patch.

Oleg.

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