From mboxrd@z Thu Jan  1 00:00:00 1970
From: Philippe Gerum <rpm@xenomai.org>
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Date: Thu, 04 Oct 2007 14:22:50 +0200
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Sender: Philippe Gerum <philippe.gerum@domain.hid>
Subject: Re: [Xenomai-core] [BUG] IO-APIC stall due to broken fasteoi
	handling
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To: Jan Kiszka <jan.kiszka@domain.hid>
Cc: adeos-main@gna.org, Xenomai-core@domain.hid

On Thu, 2007-10-04 at 11:34 +0200, Philippe Gerum wrote: 
> > Well, this trace also reveals a second bug that can cause nasty priority
> > inversion: a high-prio domains executes when a fasteoi-IRQ arrives for a
> > low-prio domain. This will now block all IRQs until the low-prio domain
> > was able to run its IRQ handler completely. Thus we must _mask_ fasteoi
> > IRQs for low-prio domains while high-prio ones are running!
> > 
> 
> This code was actually there up to 2.6.17-1.5-02, and was removed at
> some point in the 2.6.19 series, due to some severe conflicts with the
> vanilla IO-APIC support which used to be a hell of a moving target at
> that time. I guess it's time to bring this code back.
> 

Does the following work for you?

diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
index 2ae79e9..517937b 100644
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -2022,6 +2022,8 @@ static void ack_ioapic_quirk_irq(unsigned int irq)
 		__unmask_and_level_IO_APIC_irq(irq);
 		spin_unlock(&ioapic_lock);
 	}
+
+	__mask_IO_APIC_irq(irq);
 }
 
 static int ioapic_retrigger_irq(unsigned int irq)
diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
index ba497a7..1560b4a 100644
--- a/kernel/irq/chip.c
+++ b/kernel/irq/chip.c
@@ -422,8 +422,13 @@ handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc)
 
 	spin_lock(&desc->lock);
 	desc->status &= ~IRQ_INPROGRESS;
+#ifdef CONFIG_IPIPE
+	desc->chip->unmask(irq);
+out:
+#else
 out:
 	desc->chip->eoi(irq);
+#endif
 
 	spin_unlock(&desc->lock);
 }
@@ -533,11 +538,12 @@ void fastcall __ipipe_end_level_irq(unsigned irq, struct irq_desc *desc)
 
 void fastcall __ipipe_ack_fasteoi_irq(unsigned irq, struct irq_desc *desc)
 {
+	desc->chip->eoi(irq);
 }
 
 void fastcall __ipipe_end_fasteoi_irq(unsigned irq, struct irq_desc *desc)
 {
-	desc->chip->eoi(irq);
+	desc->chip->unmask(irq);
 }
 
 void fastcall __ipipe_ack_edge_irq(unsigned irq, struct irq_desc *desc)

-- 
Philippe.