linux-kernel - Re: Random panic in load

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Date:	Wed, 23 Jul 2014 10:28:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Michel Dänzer <michel@...nzer.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Random panic in load_balance() with 3.16-rc

On Wed, Jul 23, 2014 at 05:05:24PM +0900, Michel Dänzer wrote:
> On 23.07.2014 15:49, Peter Zijlstra wrote:
> Attached. No FAIL messages yet.

> [    0.467570] __sdt_alloc: allocated ffff8802155ea4c0 with cpus: 
> [    0.467574] __sdt_alloc: allocated ffff8802155ea3c0 with cpus: 
> [    0.467576] __sdt_alloc: allocated ffff8802155ea2c0 with cpus: 
> [    0.467577] __sdt_alloc: allocated ffff8802155ea1c0 with cpus: 
> [    0.467582] __sdt_alloc: allocated ffff8802155ea0c0 with cpus: 
> [    0.467589] __sdt_alloc: allocated ffff880215798f40 with cpus: 
> [    0.467591] __sdt_alloc: allocated ffff880215798e40 with cpus: 
> [    0.467593] __sdt_alloc: allocated ffff880215798d40 with cpus: 
> [    0.467599] __sdt_alloc: allocated ffff880215798c40 with cpus: 
> [    0.467600] __sdt_alloc: allocated ffff880215798b40 with cpus: 
> [    0.467602] __sdt_alloc: allocated ffff880215798a40 with cpus: 
> [    0.467604] __sdt_alloc: allocated ffff880215798940 with cpus: 
> [    0.467627] build_sched_domain: cpu: 0 level: SMT cpu_map: 0-3 tl->mask: 0-1
> [    0.467629] build_sched_domain: cpu: 0 level: MC cpu_map: 0-3 tl->mask: 0-3
> [    0.467631] build_sched_domain: cpu: 1 level: SMT cpu_map: 0-3 tl->mask: 0-1
> [    0.467632] build_sched_domain: cpu: 1 level: MC cpu_map: 0-3 tl->mask: 0-3
> [    0.467634] build_sched_domain: cpu: 2 level: SMT cpu_map: 0-3 tl->mask: 2-3
> [    0.467635] build_sched_domain: cpu: 2 level: MC cpu_map: 0-3 tl->mask: 0-3
> [    0.467637] build_sched_domain: cpu: 3 level: SMT cpu_map: 0-3 tl->mask: 2-3
> [    0.467638] build_sched_domain: cpu: 3 level: MC cpu_map: 0-3 tl->mask: 0-3
> [    0.467640] build_sched_groups: got group ffff8802155ea4c0 with cpus: 
> [    0.467642] build_sched_groups: got group ffff8802155ea3c0 with cpus: 
> [    0.467643] build_sched_groups: got group ffff8802155ea0c0 with cpus: 
> [    0.467644] build_sched_groups: got group ffff880215798e40 with cpus: 
> [    0.467646] build_sched_groups: got group ffff8802155ea2c0 with cpus: 
> [    0.467647] build_sched_groups: got group ffff8802155ea1c0 with cpus: 

Hmm, indeed. And given that I don't see how the cpumask_clear() can make
any difference for you. And your topology information is 'correct'.

Of course, the other thing that patch did is clear sgp->power (now
sgc->capacity). So does adding that back cure things for you?

If it does, we've got to go figure out what's wrong with the sgc
assignments or so.

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

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7bc599dc4aa4..0c83265cf7c6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5857,6 +5857,7 @@ build_sched_groups(struct sched_domain *sd, int cpu)
 			continue;
 
 		group = get_group(i, sdd, &sg);
+		sg->sgc->capacity = 0;
 		cpumask_setall(sched_group_mask(sg));
 
 		for_each_cpu(j, span) {
--
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