linux-kernel - Re: [PATCH 1/4] cpumask: Migrate 'alloc_cpumask_var()' users to 'zalloc_cpumask

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Date:	Mon, 7 Dec 2015 17:28:59 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Peter Zijlstra <peterz@...radead.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Xunlei Pang <xlpang@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/4] cpumask: Migrate 'alloc_cpumask_var()' users to 'zalloc_cpumask_var()'

On Mon, Dec 7, 2015 at 12:49 AM, Ingo Molnar <mingo@...nel.org> wrote:
> Xunlei Pang reported a scheduler bug in init_rootdomain(), which is
> caused by improper use of alloc_cpumask_var(), which results in
> uninitialized cpumasks being allocated.
>
> No-one noticed this scheduler bug for a long time, probably because
> alloc_cpumask_var() does result in initialized cpumasks in the
> !CPUMASK_OFFSTACK case - which is the vast majority of systems
> out there.
>
> So migrate all alloc_cpumask_var() users over to zalloc_cpumask_var(),
> to be on the safe side.

Ugh. I'd rather just see us say that "allocating a cpumask always
returns a zeroed mask".

There really is no reason to ever not zero it (they aren't _that_ big
even on huge machines), so I'd rather just get rid of the "zalloc"
version that is the less common one anyway.

                 Linus
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