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

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Message-ID: <20080205165936.GA18613@dwalker1.mvista.com>
Date:	Tue, 5 Feb 2008 08:59:36 -0800
From:	Daniel Walker <dwalker@...lker1.mvista.com>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users@...r.kernel.org,
	Max Krasnyanskiy <maxk@...lcomm.com>
Subject: Re: CPU hotplug and IRQ affinity with 2.6.24-rt1

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() ..

Daniel
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