linux-kernel - Re: CPU hotplug and IRQ affinity with 2.6.24-rt1

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Message-Id: <47A896FB.BA47.005A.0@novell.com>
Date:	Tue, 05 Feb 2008 15:03:55 -0700
From:	"Gregory Haskins" <ghaskins@...ell.com>
To:	<dwalker@...sta.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Max Krasnyanskiy" <maxk@...lcomm.com>,
	"LKML" <linux-kernel@...r.kernel.org>,
	<linux-rt-users@...r.kernel.org>
Subject: Re: CPU hotplug and IRQ affinity with 2.6.24-rt1

>>> On Tue, Feb 5, 2008 at  4:58 PM, in message
<20080205215805.GD18613@...lker1.mvista.com>, Daniel Walker
<dwalker@...lker1.mvista.com> wrote: 
> On Tue, Feb 05, 2008 at 11:25:18AM -0700, Gregory Haskins wrote:
>> @@ -6241,7 +6242,7 @@ static void rq_attach_root(struct rq *rq, struct 
> root_domain *rd)
>>                 cpu_clear(rq->cpu, old_rd->online);
>> 
>>                 if (atomic_dec_and_test(&old_rd->refcount))
>> -                       kfree(old_rd);
>> +                       reap = old_rd;
> 
> Unrelated to the in atomic issue, I was wondering if this if statement
> isn't true can the old_rd memory get leaked, or is it cleaned up
> someplace else?

Each RQ always has a reference to one root-domain and is thus represented by the rd->refcount.  When the last RQ drops its reference to a particular instance, we free the structure.  So this is the only place where we clean up, but it should also be the only place we need to (unless I am misunderstanding you?)

Note that there is one exception: the default root-domain is never freed, which is why we initialize it with a refcount = 1.  So it is theoretically possible to have this particular root-domain dangling with no RQs associated with it, but that is by design. 

Regards,
-Greg

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