Re: [tip:sched/urgent] sched: Check sched_domain before computing group power

From: Peter Zijlstra <peterz@infradead.org>
To: Yinghai Lu <yinghai@kernel.org>
Cc: David Rientjes <rientjes@google.com>,
	Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	srikar@linux.vnet.ibm.com, Thomas Gleixner <tglx@linutronix.de>,
	"linux-tip-commits@vger.kernel.org" 
	<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:sched/urgent] sched: Check sched_domain before computing group power
Date: Tue, 10 Dec 2013 11:58:20 +0100	[thread overview]
Message-ID: <20131210105820.GC12849@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CAE9FiQW53FvCUGnax0CVdrWL8wqd4wweEfQVZgJciivAYaD1yw@mail.gmail.com>

On Thu, Dec 05, 2013 at 10:24:25PM -0800, Yinghai Lu wrote:
> ---
>  kernel/sched/core.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> Index: linux-2.6/kernel/sched/core.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched/core.c
> +++ linux-2.6/kernel/sched/core.c
> @@ -5737,6 +5737,9 @@ static int __sdt_alloc(const struct cpum
>  			if (!sgp)
>  				return -ENOMEM;
>  
> +			/* avoid divide-by-zero in sg_capacity() */
> +			sgp->power_orig = 1;
> +
>  			*per_cpu_ptr(sdd->sgp, j) = sgp;
>  		}
>  	}


Ooh, sg_capacity() is generating the /0.. 

Does the below work too?

---
 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 87c3bc47d99d..40b185f5a3ec 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5115,6 +5115,7 @@ build_overlap_sched_groups(struct sched_domain *sd, int cpu)
 		 * die on a /0 trap.
 		 */
 		sg->sgp->power = SCHED_POWER_SCALE * cpumask_weight(sg_span);
+		sg->sgp->power_orig = sg->sgp->power;
 
 		/*
 		 * Make sure the first group of this domain contains the
