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

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Message-Id: <47A852E8.BA47.005A.0@novell.com>
Date:	Tue, 05 Feb 2008 10:13:28 -0700
From:	"Gregory Haskins" <ghaskins@...ell.com>
To:	"Daniel Walker" <dwalker@...lker1.mvista.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 11:59 AM, in message
<20080205165936.GA18613@...lker1.mvista.com>, Daniel Walker
<dwalker@...lker1.mvista.com> wrote: 
> On Mon, Feb 04, 2008 at 10:02:12PM -0700, Gregory Haskins wrote:
>> >>> On Mon, Feb 4, 2008 at  9:51 PM, in message
>> <20080205025144.GA31774@...lker1.mvista.com>, Daniel Walker
>> <dwalker@...lker1.mvista.com> wrote: 
>> > I get the following when I tried it,
>> > 
>> > BUG: sleeping function called from invalid context bash(5126) at
>> > kernel/rtmutex.c:638
>> > in_atomic():1 [00000001], irqs_disabled():1
>> 
>> Hi Daniel,
>>   Can you try this patch and let me know if it fixes your problem?
>> 
>> -----------------------
>> 
>> use rcu for root-domain kfree
>> 
>> Signed-off-by: Gregory Haskins <ghaskins@...ell.com>
>> 
>> diff --git a/kernel/sched.c b/kernel/sched.c
>> index e6ad493..77e86c1 100644
>> --- a/kernel/sched.c
>> +++ b/kernel/sched.c
>> @@ -339,6 +339,7 @@ struct root_domain {
>>         atomic_t refcount;
>>         cpumask_t span;
>>         cpumask_t online;
>> +       struct rcu_head rcu;
>> 
>>         /*
>>          * The "RT overload" flag: it gets set if a CPU has more than
>> @@ -6222,6 +6223,12 @@ sd_parent_degenerate(struct sched_domain *sd, struct 
> sched_domain *parent)
>>         return 1;
>>  }
>> 
>> +/* rcu callback to free a root-domain */
>> +static void rq_free_root(struct rcu_head *rcu)
>> +{
>> +       kfree(container_of(rcu, struct root_domain, rcu));
>> +}
>> +
> 
> I looked at the code a bit, and I'm not sure you need this complexity..
> Once you have replace the old_rq, there is no reason it needs to
> protection of the run queue spinlock .. So you could just move the kfree
> down below the spin_unlock_irqrestore() ..

Indeed.  When I looked last night at the stack, I thought the in_atomic was coming from further up in the trace.  I see the issue now, thanks Daniel.  (Anyone have a spare brown bag?)

-Greg

> 
> Daniel
> -
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