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Date: Tue, 20 Feb 2007 23:09:36 +0300
From: Oleg Nesterov <oleg@tv-sign.ru>
To: Srivatsa Vaddagiri <vatsa@in.ibm.com>
Cc: Gautham R Shenoy <ego@in.ibm.com>, akpm@osdl.org, paulmck@us.ibm.com,
       mingo@elte.hu, dipankar@in.ibm.com, venkatesh.pallipadi@intel.com,
       linux-kernel@vger.kernel.org, rjw@sisk.pl
Subject: Re: [RFC PATCH(Experimental) 2/4] Revert changes to workqueue.c
Message-ID: <20070220200936.GB85@tv-sign.ru>
References: <20070214144229.GA19789@in.ibm.com> <20070214144305.GB19789@in.ibm.com> <20070214200904.GB301@tv-sign.ru> <20070216052626.GB8373@in.ibm.com> <20070216153321.GB83@tv-sign.ru> <20070216164730.GD21457@in.ibm.com> <20070216235939.GB244@tv-sign.ru> <20070217022940.GB25924@in.ibm.com> <20070217215928.GA563@tv-sign.ru> <20070220151220.GB4960@in.ibm.com>
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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.