From: "Yandong.Zhao" <yandong77520@gmail.com>
To: Dave.Martin@arm.com
Cc: linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, ard.biesheuvel@linaro.org,
will.deacon@arm.com, catalin.marinas@arm.com,
zhaoyd@thundersoft.com, zhaoxb@thundersoft.com,
fanlc0801@thundersoft.com, Yandong Zhao <yandong77520@gmail.com>
Subject: [PATCH] arm64: neon: Fix function may_use_simd() return error status
Date: Wed, 11 Jul 2018 19:06:28 +0800 [thread overview]
Message-ID: <1531307188-12032-1-git-send-email-yandong77520@gmail.com> (raw)
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.
Fixes: cb84d11e1625 ("arm64: neon: Remove support for nested or hardirq kernel-mode NEON")
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
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..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 reply other threads:[~2018-07-11 11:06 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-11 11:06 Yandong.Zhao [this message]
2018-07-11 12:05 ` [PATCH] arm64: neon: Fix function may_use_simd() return error status Will Deacon
2018-07-11 12:58 ` 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 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
2018-07-10 2:21 Yandong.Zhao
2018-07-10 13:11 ` Dave Martin
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