linux-kernel - Re: [RFC PATCH v6 3/3] arm: fix a migrating irq bug when hotplug cpu

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Date:	Thu, 22 Oct 2015 11:46:08 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Mark Rutland <mark.rutland@....com>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Yang Yingliang <yangyingliang@...wei.com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RFC PATCH v6 3/3] arm: fix a migrating irq bug when hotplug cpu

Hi Russell,

On Thu, Oct 22, 2015 at 11:26 AM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Wed, Oct 21, 2015 at 09:29:08PM +0100, Russell King - ARM Linux wrote:
>> On Wed, Oct 21, 2015 at 01:47:49PM +0200, Geert Uytterhoeven wrote:
>> > On Thu, Sep 24, 2015 at 11:32 AM, Yang Yingliang
>> > <yangyingliang@...wei.com> wrote:
>> > > When cpu is disabled, all irqs will be migratged to another cpu.
>> > > In some cases, a new affinity is different, the old affinity need
>> > > to be updated and if irq_set_affinity's return value is IRQ_SET_MASK_OK_DONE,
>> > > the old affinity can not be updated. Fix it by using irq_do_set_affinity.
>> > >
>> > > And migrating interrupts is a core code matter, so use the generic
>> > > function irq_migrate_all_off_this_cpu() to migrate interrupts in
>> > > kernel/irq/migration.c.
>> > >
>> > > Cc: Jiang Liu <jiang.liu@...ux.intel.com>
>> > > Cc: Thomas Gleixner <tglx@...utronix.de>
>> > > Cc: Marc Zyngier <marc.zyngier@....com>
>> > > Cc: Mark Rutland <mark.rutland@....com>
>> > > Cc: Will Deacon <will.deacon@....com>
>> > > Cc: Russell King - ARM Linux <linux@....linux.org.uk>
>> > > Cc: Hanjun Guo <hanjun.guo@...aro.org>
>> > > Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
>> > > ---
>> > >  arch/arm/Kconfig           |  1 +
>> > >  arch/arm/include/asm/irq.h |  1 -
>> > >  arch/arm/kernel/irq.c      | 62 ----------------------------------------------
>> > >  arch/arm/kernel/smp.c      |  2 +-
>> > >  4 files changed, 2 insertions(+), 64 deletions(-)
>> > >
>> > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> > > index 72ad724..bffba78 100644
>> > > --- a/arch/arm/Kconfig
>> > > +++ b/arch/arm/Kconfig
>> > > @@ -1492,6 +1492,7 @@ config NR_CPUS
>> > >  config HOTPLUG_CPU
>> > >         bool "Support for hot-pluggable CPUs"
>> > >         depends on SMP
>> > > +       select GENERIC_IRQ_MIGRATION
>> >
>> > This causes the following warnings during s2ram on r8a7791/koelsch
>> > (dual-core CA15):
>>
>> Thanks for the report.  I'll see what tonight's boot run says for my
>> platforms.  Hopefully, the author of these changes can help debug
>> this.
>
> What's happened is that:
>
> -       c = irq_data_get_irq_chip(d);
> -       if (!c->irq_set_affinity)
> -               pr_debug("IRQ%u: unable to set affinity\n", d->irq);
>
> has become:
>
> +       c = irq_data_get_irq_chip(d);
> +       if (!c->irq_set_affinity) {
> +               pr_warn_ratelimited("IRQ%u: unable to set affinity\n", d->irq);
>
> which makes things more noisy.
>
> This is a change that was not described in the commit message for the
> patch Thomas merged.
>
> So, I think the right thing to do is to drop the patch set and revert
> back to what we knew was sane, and get the submitter to do the job
> properly: cleanly move the code from one location to another with _no_
> changes what so ever, convert ARM and ARM64 to use it, and _then_ to
> modify the resulting code.
>
> From what I can see, both ARM and ARM64 implementations here are
> identical.
>
> I'm certainly dropping this from the ARM tree.

Thanks for your analysis!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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