[PATCH] arm: use irq_set_affinity with force=false when migrating irqs

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Mon, Sep 01, 2014 at 12:46:06PM +0100, Sudeep Holla wrote:
> From: Sudeep Holla <sudeep.holla@arm.com>
> 
> Commit 01f8fa4f01d8("genirq: Allow forcing cpu affinity of interrupts")
> enabled the forced irq_set_affinity which previously refused to route an
> interrupt to an offline cpu.
> 
> Commit ffde1de64012("irqchip: Gic: Support forced affinity setting")
> implements this force logic and disables the cpu online check for GIC
> interrupt controller.
> 
> When __cpu_disable calls migrate_irqs, it disables the current cpu in
> cpu_online_mask and uses forced irq_set_affinity to migrate the IRQs
> away from the cpu but passes affinity mask with the cpu being offlined
> also included in it.
> 
> If irq_set_affinity is called with force=true in a cpu hotplug path,
> the caller must ensure that the cpu being offlined is not present in the
> affinity mask or it may be selected as the target CPU, leading to the
> interrupt not being migrated.
> 
> This patch fixes the issue by calling irq_set_affinity with force=false
> so that cpu_online_mask is checked while setting the affinity in the
> cpu hotplug path.
> 
> Tested on TC2 hotpluging CPU0 in and out. Without this patch the system
> locks up as the IRQs are not migrated away from CPU0.
> 
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: <stable@vger.kernel.org> # 3.10.x
> ---
>  arch/arm/kernel/irq.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Hi Russell,
> 
> If you or tglx has no objections to this patch, I will put it
> in your patch tracker.

Post discussion, I have no objections - except to the above comment.  Let
me rewrite it in a programming language, and maybe you can spot what's
wrong:

	if (russell_has_no_objection(patch) || tglx_has_no_objection(patch))
		submit_patch_to_tracker(patch);

Personally, I'd like to see tglx's ack on this first.

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