From mboxrd@z Thu Jan  1 00:00:00 1970
From: tglx@linutronix.de (Thomas Gleixner)
Date: Mon, 25 Aug 2014 11:55:48 +0200 (CEST)
Subject: [PATCH] arm: use cpu_online_mask when using forced
 irq_set_affinity
In-Reply-To: <53C79E43.6040009@arm.com>
References: <1399653640-21559-1-git-send-email-sudeep.holla@arm.com>
 <20140523121032.GV3693@n2100.arm.linux.org.uk> <537F4453.5000709@arm.com>
 <53A43174.503@arm.com> <20140620151638.GS32514@n2100.arm.linux.org.uk>
 <53C79E43.6040009@arm.com>
Message-ID: <alpine.DEB.2.10.1408251136380.3323@nanos>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, 17 Jul 2014, Sudeep Holla wrote:
> > > Any suggestions on this ? Since commit 01f8fa4f01d8 and ffde1de64012 are
> > > now in
> > > stable releases, CPU0 hotplug is broken there now.
> > 
> > Maybe we should ask Thomas, as he's (a) the maintainer of the irqchip
> > stuff, and (b) the author of the patch causing the breakage.
> > 
> >  From what I can see looking at the x86 code, the work-around in
> > ffde1de64012 is wrong.
> > 
> 
> Can provide your thoughts on how to solve this issue ?

ffde1de64012 is not about offlining a cpu, it's about onlining where
we need to make sure that we assign the affinity to a not yet online
marked cpu.
 
> Is it expected from all the irqchip implementation to use force flag in
> irq_set_affinity to ignore cpu_online_mask similar to GIC ?

No, it's only relevant for the cases where we need to route irqs to
not yet online cpus.

Now the wreckage of offlining was definitely not intended and I wonder
why set_affinity() is called there with force = true. This was
introduced in commit 1dbfa187dad. I acked it back then, but I have no
idea why, because the force argument did not have any effect at that
time.

Changing it to false should solve the issue.

Thanks,

	tglx

diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index 2c4257604513..5c4d38e32a51 100644
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -175,7 +175,7 @@ static bool migrate_one_irq(struct irq_desc *desc)
 	c = irq_data_get_irq_chip(d);
 	if (!c->irq_set_affinity)
 		pr_debug("IRQ%u: unable to set affinity\n", d->irq);
-	else if (c->irq_set_affinity(d, affinity, true) == IRQ_SET_MASK_OK && ret)
+	else if (c->irq_set_affinity(d, affinity, false) == IRQ_SET_MASK_OK && ret)
 		cpumask_copy(d->affinity, affinity);
 
 	return ret;