linux-kernel - Re: [RFC][PATCH] Add __GFP_ZERO to alloc_cpumask_var

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Date:	Fri, 4 Dec 2015 08:34:37 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Xunlei Pang <xlpang@...hat.com>
Subject: Re: [RFC][PATCH] Add __GFP_ZERO to alloc_cpumask_var_node() if ptr
 is zero


* Steven Rostedt <rostedt@...dmis.org> wrote:

> On Fri, 04 Dec 2015 12:05:12 +1030
> Rusty Russell <rusty@...tcorp.com.au> wrote:
> 
> > This is clever, but I would advise against such subtle code.  We will never be 
> > able to remove this code once it is in.
> > 
> > Would suggest making the non-CPUMASK_OFFSTACK stubs write garbage into the 
> > cpumasks instead, iff !(flags & __GFP_ZERO).
>
> I actually thought of the same thing, but thought it was a bit harsh. If others 
> think that's a better solution, then I'll submit a patch to do that.

That just makes things more fragile - 'garbage' will spread the breakage, and if 
the breakage is subtle, it will spread subtle breakage.

So why not use a kzmalloc_node() [equivalent] call instead of kmalloc_node(), to 
make sure it's all zeroed instead of uninitialized?

Thanks,

	Ingo
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