Re: [PATCH v2 08/10] perf/hisi_uncore: Avoid placing cpumask var on stack

Jonathan Cameron
2024-04-05T09:53:42Z

On Wed, 3 Apr 2024 15:35:47 +0100
Mark Rutland <mark.rutland@arm.com> wrote:

> On Wed, Apr 03, 2024 at 08:51:07PM +0800, Dawei Li wrote:
> > For CONFIG_CPUMASK_OFFSTACK=y kernel, explicit allocation of cpumask
> > variable on stack is not recommended since it can cause potential stack
> > overflow.
> >
> > Instead, kernel code should always use *cpumask_var API(s) to allocate
> > cpumask var in config-neutral way, leaving allocation strategy to
> > CONFIG_CPUMASK_OFFSTACK.
> >
> > But dynamic allocation in cpuhp's teardown callback is somewhat problematic
> > for if allocation fails(which is unlikely but still possible):
> > - If -ENOMEM is returned to caller, kernel crashes for non-bringup
> > teardown;
> > - If callback pretends nothing happened and returns 0 to caller, it may
> > trap system into an in-consisitent/compromised state;
> >
> > Use newly-introduced cpumask_any_and_but() to address all issues above.
> > It eliminates usage of temporary cpumask var in generic way, no matter how
> > the cpumask var is allocated.
> >
> > Suggested-by: Mark Rutland <mark.rutland@arm.com>
> > Signed-off-by: Dawei Li <dawei.li@shingroup.cn>
>
> The logic looks good to me, but I'd like the commit message updated the same as
> per my comment on patch 2.
>
> With that commit message:
>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>

Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>