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

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Date:	Tue, 05 Feb 2008 11:25:18 -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 11:59 AM, in message
<20080205165936.GA18613@...lker1.mvista.com>, Daniel Walker
<dwalker@...lker1.mvista.com> wrote: 

> 
> 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() ..

Here is a new version to address your observation:
-----------------------

we cannot kfree while in_atomic()

Signed-off-by: Gregory Haskins <ghaskins@...ell.com>

diff --git a/kernel/sched.c b/kernel/sched.c
index e6ad493..0978912 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6226,6 +6226,7 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd)
 {
        unsigned long flags;
        const struct sched_class *class;
+       struct root_domain *reap = NULL;

        spin_lock_irqsave(&rq->lock, flags);

@@ -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;
        }

        atomic_inc(&rd->refcount);
@@ -6257,6 +6258,10 @@ static void rq_attach_root(struct rq *rq, struct root_domain *rd)
        }

        spin_unlock_irqrestore(&rq->lock, flags);
+
+       /* Don't try to free the memory while in-atomic() */
+       if (unlikely(reap))
+               kfree(reap);
 }




> 
> Daniel
> -
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