From: Will Deacon <will.deacon@arm.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Dave Martin <Dave.Martin@arm.com>,
"Yandong.Zhao" <yandong77520@gmail.com>,
linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
zhaoyd@thundersoft.com, zhaoxb@thundersoft.com,
fanlc0801@thundersoft.com
Subject: Re: [PATCH] arm64: neon: Fix function may_use_simd() return error status
Date: Wed, 11 Jul 2018 17:03:15 +0100 [thread overview]
Message-ID: <20180711160315.GD18477@arm.com> (raw)
In-Reply-To: <20180711154758.4k2phfrzl2r5m34o@lakrids.cambridge.arm.com>
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 <yandong77520@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.rutland@arm..com>
Thanks. Applied with the updated comment and your tag..
Will
next prev parent reply other threads:[~2018-07-11 16:02 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-11 1:09 [PATCH] arm64: neon: Fix function may_use_simd() return error status Yandong.Zhao
2018-07-11 7:20 ` Ard Biesheuvel
2018-07-11 15:47 ` Mark Rutland
2018-07-11 16:03 ` Will Deacon [this message]
2018-07-11 16:07 ` Mark Rutland
2018-07-11 10:55 ` Dave Martin
-- strict thread matches above, loose matches on Subject: below --
2018-07-12 3:29 Yandong.Zhao
2018-07-12 9:56 ` Dave Martin
2018-07-11 11:06 Yandong.Zhao
2018-07-11 12:05 ` Will Deacon
2018-07-11 12:58 ` Dave Martin
2018-07-10 2:21 Yandong.Zhao
2018-07-10 13:11 ` Dave Martin
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