linux-kernel - Re: Random panic in load

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Message-ID: <CA+55aFwyURgG717kmuAXzKcHddN_63GirtwHZB4ePKH+8qVtJw@mail.gmail.com>
Date:	Tue, 22 Jul 2014 21:21:40 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Michel Dänzer <michel@...nzer.net>
Cc:	Peter Zijlstra <peterz@...radead.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 Tue, Jul 22, 2014 at 8:53 PM, Michel Dänzer <michel@...nzer.net> wrote:
>
> Just happened again with the same change on top of 3.16-rc6.

The (maybe) related bugzilla entry is just odd. Bruno Wolff reports
that the BUG_ON() in his added patch triggers:

+               cpumask_clear(sched_group_cpus(sg));
+               sg->sgc->capacity = 0;
+               BUG_ON(!cpumask_empty(sched_group_cpus(sg)));

where it *just* did a cpumask_clear(), and now the BUG_ON() triggers
that it's no longer empty?

That would imply an allocation error, but all the sched groups seem to
be properly allocated with the proper addition of cpumask_size().

And his config file even has NR_CPUS being 32, so it should be a
single word of bitmap, which triggers all the simple code.

Completely insane, in other words.

           Linus
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