Re: [PATCH] cpumask: alloc blank cpumask left over

Yinghai Lu
2009-06-06T09:37:44Z

Avi Kivity wrote:
> Rusty Russell wrote:
>> On Fri, 5 Jun 2009 03:26:57 pm Yinghai Lu wrote:
>>
>>> Rusty Russell wrote:
>>>
>>>> On Fri, 5 Jun 2009 06:31:31 am Yinghai Lu wrote:
>>>>
>>>>> avoid suprise when MAXSMP is enabled
>>>>>
>>>>> Signed-off-by: Yinghai Lu <yinghai.lu@kernel.org>
>>>>>
>>>> I understand the temptation, but two questions arise:
>>>> 1) Shouldn't we actually audit to see if any of these are currently
>>>> problems,
>>>>
>>> those are defined as static cpumask_var_t, and if MAXSMP is not used,
>>> they
>>> are cleared already
>>>
>>
>> OK, here's what I've got in my tree. Ingo, I think this should go in the
>> current -rc to avoid nasty bugs.
>>
>> BTW, the original alloc_cpumask_var did zero; that was dropped after
>> arguments
>> over efficiency and fitting with other interfaces, but I clearly had
>> the old
>> semantics in my head for a while.
>>
>>
>
> Using __GFP_ZERO is equivalent to using memset() instead of
> cpumask_clear(). It's better to call cpumask_clear() or provide an API
> to alloc+clear.
>
> Further, what about the non-MAXSMP case:
>
>
> static inline bool alloc_cpumask_var(cpumask_var_t *mask, gfp_t flags)
> {
> return true;
> }
>
>
> We explicity clear on MAXSMP and rely on static initialization for the
> non-MAXSMP, laying a neat trap for anyone who makes the variable
> non-static. Let's be less subtle that that.

or have zalloc_cpumask_var() ?

YH