From: Dave Martin <Dave.Martin@arm.com>
To: "Yandong.Zhao" <yandong77520@gmail.com>
Cc: zhaoxb@thundersoft.com, ard.biesheuvel@linaro.org,
catalin.marinas@arm.com, will.deacon@arm.com,
linux-kernel@vger.kernel.org, zhaoyd@thundersoft.com,
linux-arm-kernel@lists.infradead.org, fanlc0801@thundersoft.com
Subject: Re: [PATCH] arm64: neon: Fix function may_use_simd() return error status
Date: Tue, 10 Jul 2018 14:11:20 +0100 [thread overview]
Message-ID: <20180710131119.GI9486@e103592.cambridge.arm.com> (raw)
In-Reply-To: <1531189300-26216-1-git-send-email-yandong77520@gmail.com>
On Tue, Jul 10, 2018 at 10:21:40AM +0800, Yandong.Zhao wrote:
> From: Yandong Zhao <yandong77520@gmail.com>
>
> Operations for contexts where we do not want to do any checks for
> preemptions. Unless strictly necessary, always use this_cpu_read()
> instead. Because of the kernel_neon_busy here we have to make sure
> that it is the current cpu.
I find this wording a bit confusing.
Does the following make look OK to you?
--8<--
It does not matter if the caller of may_use_simd() migrates to
another cpu after the call, but it is still important that the
kernel_neon_busy percpu instance that is read matches the cpu the
task is running on at the time of the read.
This means that raw_cpu_read() is not sufficient. kernel_neon_busy
may appear true if the caller migrates during the execution of
raw_cpu_read() and the next task to be scheduled in on the initial
cpu calls kernel_neon_begin().
This patch replaces raw_cpu_read() with this_cpu_read() to protect
against this race.
-->8--
>
> Signed-off-by: Yandong Zhao <yandong77520@gmail.com>
> ---
> arch/arm64/include/asm/simd.h | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/simd.h b/arch/arm64/include/asm/simd.h
> index fa8b3fe..8b97f8b 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 my subsequently migrate to another CPU.
"my" -> "may"
(apologies if I was responsible for that typo)
[...]
Cheers
---Dave
next prev parent reply other threads:[~2018-07-10 13:11 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-10 2:21 [PATCH] arm64: neon: Fix function may_use_simd() return error status Yandong.Zhao
2018-07-10 13:11 ` Dave Martin [this message]
2018-07-11 1:09 Yandong.Zhao
2018-07-11 7:20 ` Ard Biesheuvel
2018-07-11 15:47 ` Mark Rutland
2018-07-11 16:03 ` Will Deacon
2018-07-11 16:07 ` Mark Rutland
2018-07-11 10:55 ` Dave Martin
2018-07-11 11:06 Yandong.Zhao
2018-07-11 12:05 ` Will Deacon
2018-07-11 12:58 ` Dave Martin
2018-07-12 3:29 Yandong.Zhao
2018-07-12 9:56 ` Dave Martin
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