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 10:26:30 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Thomas Gleixner <tglx@...utronix.de>
Cc:	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>,
	Thomas Gleixner <tglx@...utronix.de>,
	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

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.

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