linux-kernel - Re: Scheduler regression from caffcdd8d27ba78730d5540396ce72ad022aff2c

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Message-ID: <20140716151748.GC2460@hansolo.jdub.homelinux.org>
Date:	Wed, 16 Jul 2014 11:17:48 -0400
From:	Josh Boyer <jwboyer@...hat.com>
To:	Bruno Wolff III <bruno@...ff.to>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>
Cc:	mingo@...hat.com, peterz@...radead.org,
	linux-kernel@...r.kernel.org
Subject: Re: Scheduler regression from
 caffcdd8d27ba78730d5540396ce72ad022aff2c

Adding Dietmar in since he is the original author.

josh

On Wed, Jul 16, 2014 at 09:55:46AM -0500, Bruno Wolff III wrote:
> caffcdd8d27ba78730d5540396ce72ad022aff2c has been causing crashes
> early in the boot process on one of three machines I have been
> testing the kernel on. On that one machine it happens every boot. It
> happens before netconsole is functional.
> 
> A partial revert of the commit fixes the problem. I do not know why
> the commit is broken though.
> 
> I have filed https://bugzilla.kernel.org/show_bug.cgi?id=80251 for
> this issue.
> 
> The problem happens on both Fedora and Linus kernels.
> 
> git diff caffcdd8d27ba78730d5540396ce72ad022aff2c^ caffcdd8d27ba78730d5540396ce72ad022aff2c
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 45d077ed24fb..6340c601475d 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5794,8 +5794,6 @@ build_sched_groups(struct sched_domain *sd, int cpu)
>                        continue;
> 
>                group = get_group(i, sdd, &sg);
> -               cpumask_clear(sched_group_cpus(sg));
> -               sg->sgp->power = 0;
>                cpumask_setall(sched_group_mask(sg));
> 
>                for_each_cpu(j, span) {
> 
> By rc5 the second line can't be added back because the structure has
> changed. However adding back cpumask_clear(sched_group_cpus(sg)); to
> rc5 got things working for me again.
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