linux-kernel - Scheduler regression from caffcdd8d27ba78730d5540396ce72ad022aff2c

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Message-ID: <20140716145546.GA6922@wolff.to>
Date:	Wed, 16 Jul 2014 09:55:46 -0500
From:	Bruno Wolff III <bruno@...ff.to>
To:	mingo@...hat.com, peterz@...radead.org
Cc:	linux-kernel@...r.kernel.org, jwboyer@...hat.com
Subject: Scheduler regression from caffcdd8d27ba78730d5540396ce72ad022aff2c

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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