Re: [PATCH v7 13/22] sched: Allow task CPU affinity to be restricted on asymmetric systems

Will Deacon
2021-05-26T17:45:48Z

On Wed, May 26, 2021 at 06:20:25PM +0200, Peter Zijlstra wrote:
> On Tue, May 25, 2021 at 04:14:23PM +0100, Will Deacon wrote:
> > +static int restrict_cpus_allowed_ptr(struct task_struct *p,
> > + struct cpumask *new_mask,
> > + const struct cpumask *subset_mask)
> > +{
> > + struct rq_flags rf;
> > + struct rq *rq;
> > + int err;
> > + struct cpumask *user_mask = NULL;
> > +
> > + if (!p->user_cpus_ptr) {
> > + user_mask = kmalloc(cpumask_size(), GFP_KERNEL);
>
> if (!user_mask)
> return -ENOMEM;
> }
>
> ?

We won't blow up if we continue without user_mask here, but I agree that
it's more straightforward to return an error and have
force_compatible_cpus_allowed_ptr() noisily override the mask.

We're in pretty deep trouble if we're failing this allocation anyway.

Will