linux-kernel - Re: Random panic in load

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Message-ID: <CA+55aFwQSmBAs=QH9jAZz5JY7YFrDeuPH1RjFH+YKVr2NQM38g@mail.gmail.com>
Date:	Wed, 23 Jul 2014 10:12:35 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Dietmar Eggemann <dietmar.eggemann@....com>,
	Michel Dänzer <michel@...nzer.net>,
	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 10:03 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Jul 23, 2014 at 09:54:23AM -0700, Linus Torvalds wrote:
>>
>> And I wonder if I have a clue. Look, load_balance_mask is a
>> "cpumask_var_t", but I don't see a "alloc_cpumask_var()" for it.
>> That's broken with CONFIG_CPUMASK_OFFSTACK.
>
> kernel/sched/core.c:sched_init()
>
> plays horrible allocation tricks..

No it does not. It allocates a cpumask. Nothing more. If you think it
allocates a "cpumask_var()", you are wrong.

I agree that the code is an unreadable mess, but that's what
"cpumask_size()" is: the minimum required size of the bitmask in a
cpumask.

A cpumask_var is TOTALLY DIFFERENT. It's *either* a cpumask _or_ just
a pointer to an externally allocated cpumask.

sched_init() definitely does _not_ allocate a cpumask_var.

                Linus
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