Re: One question about API cpumask_setall()

[Bibo Mao]

On 2026/7/29 上午9:55, Yury Norov wrote:
> On Tue, Jul 28, 2026 at 04:16:27PM +0800, Bibo Mao wrote:
> > Hi,
> >
> > I am preparing to use API cpumask_setall() for TLB flush on LoongArch KVM
> > side. There are cpumask_test_and_clear_cpu/cpumask_setall() APIs, it seems
> > that API cpumask_setall() does not support atomic operation.
> >
> > Do you think it is reasonable to add new API similar with cpumask_setall()
> > which supports atomic operation?
>
> Maybe reasonable, but it's impossible. cpumask is a bitmap, which in
> turn is an array of unsigned longs. There's no atomic operations on
> arrays.
It should be workable with atomic operation on unsigned long, rather 
than the array of unsigned longs, the API cpumask_test_and_clear_cpu is 
atomic operation on unsigned long also.

Is it ok to use smp_store_mb() to fill the bitmap with the similar API 
cpumask_setall()? where xchg() is used in smp_store_mb() wrapper instead.

Regards
Bibo Mao
> Thanks,
> Yury