linux-kernel - Re: [PATCH] cpuset: Make rebuild_sched

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Message-ID: <487CDE15.1070401@qualcomm.com>
Date:	Tue, 15 Jul 2008 10:27:49 -0700
From:	Max Krasnyansky <maxk@...lcomm.com>
To:	Paul Menage <menage@...gle.com>
CC:	mingo@...e.hu, pj@....com, linux-kernel@...r.kernel.org,
	a.p.zijlstra@...llo.nl
Subject: Re: [PATCH] cpuset: Make rebuild_sched_domains() usable from any
 context

Paul Menage wrote:
> On Tue, Jul 15, 2008 at 4:44 AM, Max Krasnyansky <maxk@...lcomm.com> wrote:
>> From: Max Krasnyanskiy <maxk@...lcomm.com>
>>
>> I do not really like the current solution of dropping cgroup lock
>> but it shows what I have in mind in general.
> 
> I think that dropping the cgroup lock will open up races for cpusets.
> The idea of a separate workqueue/thread to do the sched domain
> rebuilding is simplest.

Actually I audited (to the best of my knowledge) all the paths in 
cpusets and rebuild_sched_domains() is the last action. ie We drop the 
lock right after it anyways. It's just it's embedded deep in the call 
stack and therefor I cannot drop it at the higher level.

The only path where I think it's not safe is the cgroup destroy thing 
where we do

cgroup.c
	cgroup_lock();
	for_each_cgroups(...)
		cg->destroy();
	cgroup_unlock();

So in theory it's just that one patch that really needs the workqueue 
trick. But I do agree that it'll make it less tricky across the board.
So I'll pick up you work queue based patch, convert it to single 
threaded, bang on a bit later today and send a patch on top of this one.

Max

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