From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: "Yandong.Zhao" <yandong77520@gmail.com>,
Dave Martin <Dave.Martin@arm.com>
Cc: linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Will Deacon <will.deacon@arm.com>,
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 09:20:03 +0200 [thread overview]
Message-ID: <CAKv+Gu-PLsWZLPM-OfXHLGKs7PojRB4jFsyp+X_5OW6ryi7gRQ@mail.gmail.com> (raw)
In-Reply-To: <1531271399-1768-1-git-send-email-yandong77520@gmail.com>
On 11 July 2018 at 03:09, Yandong.Zhao <yandong77520@gmail.com> wrote:
> From: Yandong Zhao <yandong77520@gmail.com>
>
> 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.
>
> Signed-off-by: Yandong Zhao <yandong77520@gmail.com>
I had a bit of trouble disentangling the per-cpu spaghetti to decide
whether this may trigger warnings when CONFIG_DEBUG_PREEMPT=y, but I
don't think so. So assuming this is *not* the case:
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> 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..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.
> @@ -42,7 +43,7 @@ static __must_check inline bool may_use_simd(void)
> * false.
> */
> return !in_irq() && !irqs_disabled() && !in_nmi() &&
> - !raw_cpu_read(kernel_neon_busy);
> + !this_cpu_read(kernel_neon_busy);
> }
>
> #else /* ! CONFIG_KERNEL_MODE_NEON */
> --
> 1.9.1
>
next prev parent reply other threads:[~2018-07-11 7:20 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 [this message]
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
-- 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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAKv+Gu-PLsWZLPM-OfXHLGKs7PojRB4jFsyp+X_5OW6ryi7gRQ@mail.gmail.com \
--to=ard.biesheuvel@linaro.org \
--cc=Dave.Martin@arm.com \
--cc=catalin.marinas@arm.com \
--cc=fanlc0801@thundersoft.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=will.deacon@arm.com \
--cc=yandong77520@gmail.com \
--cc=zhaoxb@thundersoft.com \
--cc=zhaoyd@thundersoft.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).