On Wed, Jul 11, 2018 at 04:47:58PM +0100, Mark Rutland wrote:
> On Wed, Jul 11, 2018 at 09:20:03AM +0200, Ard Biesheuvel wrote:
> > On 11 July 2018 at 03:09, Yandong.Zhao <yandong77...@gmail.com> wrote:
> > > diff --git a/arch/arm64/include/asm/simd.h b/arch/arm64/include/asm/simd.h
> > > index fa8b3fe..784a8c2 100644
> > > --- a/arch/arm64/include/asm/simd.h
> > > +++ b/arch/arm64/include/asm/simd.h
> > > @@ -29,7 +29,8 @@
> > > static __must_check inline bool may_use_simd(void)
> > > {
> > > /*
> > > - * The raw_cpu_read() is racy if called with preemption enabled.
> > > + * The this_cpu_read() is racy if called with preemption enabled,
> > > + * since the task may subsequently migrate to another CPU.
> > > * This is not a bug: kernel_neon_busy is only set when
> > > * preemption is disabled, so we cannot migrate to another CPU
> > > * while it is set, nor can we migrate to a CPU where it is set.
>
> It would be nice if we could clarify the "is racy" part here.
>
> How about:
>
> /*
> * kernel_neon_busy is only set while preemption is disabled,
> * and is clear whenever preemption is enabled. Since
> * this_cpu_read() is atomic w.r.t. preemption, kernel_neon_busy
> * cannot change under our feet -- if it's set we cannot be
> * migrated, and if it's clear we cannot be migrated to a CPU
> * where it is set.
> */
>
> With that:
>
> Reviewed-by: Mark Rutland <mark.rutl...@arm..com>
Thanks. Applied with the updated comment and your tag..
Will
