linux-kernel - Re: [PATCH 1/3] clocksource: exynos_mct: Fix stall after CPU hotplugging

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Message-ID: <alpine.DEB.2.02.1404151711250.22697@ionos.tec.linutronix.de>
Date:	Tue, 15 Apr 2014 17:20:04 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Tomasz Figa <t.figa@...sung.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/3] clocksource: exynos_mct: Fix stall after CPU
 hotplugging

On Tue, 15 Apr 2014, Krzysztof Kozlowski wrote:

> On wto, 2014-04-15 at 14:28 +0200, Daniel Lezcano wrote:
> > On 04/15/2014 11:34 AM, Krzysztof Kozlowski wrote:
> > > On pią, 2014-03-28 at 14:06 +0100, Krzysztof Kozlowski wrote:
> > >> Fix stall after hotplugging CPU1. Affected are SoCs where Multi Core Timer
> > >> interrupts are shared (SPI), e.g. Exynos 4210. The stall was a result of
> > >> starting the CPU1 local timer not in L1 timer but in L0 (which is used
> > >> by CPU0).
> > >
> > > Hi,
> > >
> > > Do you have any comments on these 3 patches? They fix the CPU stall on
> > > Exynos4210 and also on Exynos3250 (Chanwoo Choi sent patches for it
> > > recently).
> > 
> > You describe this issue as impacting different SoC not only the exynos, 
> > right ?
> >
> > Do you know what other SoCs are impacted by this ?
> 
> No, affected are only Exynos SoC-s. It was confirmed on Exynos4210
> (Trats board) and Exynos3250 (new SoC, patches for it were recently
> posted by Chanwoo).
> 
> Other Exynos SoC-s where MCT local timers use shared interrupts (SPI)
> can also be affected. Candidates are Exynos 5250 and 5420 but I haven't
> tested them.
> 
> > I guess this issue is not reproducible just with the line below, we need 
> > a timer to expire right at the moment CPU1 is hotplugged, right ?
> 
> Right. The timer must fire in short time between enabling local timer
> for CPU1 and setting the affinity for IRQ.

Why do you set the affinity in the CPU_ONLINE hotplug callback and not
right away when the interrupt is requested?

Thanks,

	tglx


Index: linux-2.6/drivers/clocksource/exynos_mct.c
===================================================================
--- linux-2.6.orig/drivers/clocksource/exynos_mct.c
+++ linux-2.6/drivers/clocksource/exynos_mct.c
@@ -430,6 +430,7 @@ static int exynos4_local_timer_setup(str
 				evt->irq);
 			return -EIO;
 		}
+		irq_set_affinity(mct_irqs[MCT_L0_IRQ + cpu], cpumask_of(cpu));
 	} else {
 		enable_percpu_irq(mct_irqs[MCT_L0_IRQ], 0);
 	}
@@ -461,12 +462,6 @@ static int exynos4_mct_cpu_notify(struct
 		mevt = this_cpu_ptr(&percpu_mct_tick);
 		exynos4_local_timer_setup(&mevt->evt);
 		break;
-	case CPU_ONLINE:
-		cpu = (unsigned long)hcpu;
-		if (mct_int_type == MCT_INT_SPI)
-			irq_set_affinity(mct_irqs[MCT_L0_IRQ + cpu],
-						cpumask_of(cpu));
-		break;
 	case CPU_DYING:
 		mevt = this_cpu_ptr(&percpu_mct_tick);
 		exynos4_local_timer_stop(&mevt->evt);