On Wed, Jul 11, 2018 at 05:03:15PM +0100, Will Deacon wrote:
> 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..
Cheer!
Mar.
