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

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Date:	Tue, 8 Dec 2015 05:09:03 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.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()'


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 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.

Sure - that was my original suggestion, will reshape the series to do it like 
that.

Thanks,

	Ingo
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