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

[Avi Kivity]

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@xxxxxxxxxx>
> > > >         
> > > 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.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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