This is a note to let you know that I've just added the patch titled
ARM: 7955/1: spinlock: ensure we have a compiler barrier before sev
to the 3.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm-7955-1-spinlock-ensure-we-have-a-compiler-barrier-before-sev.patch
and it can be found in the queue-3.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 7c8746a9eb287642deaad0e7c2cdf482dce5e4be Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@xxxxxxx>
Date: Fri, 7 Feb 2014 19:12:32 +0100
Subject: ARM: 7955/1: spinlock: ensure we have a compiler barrier before sev
From: Will Deacon <will.deacon@xxxxxxx>
commit 7c8746a9eb287642deaad0e7c2cdf482dce5e4be upstream.
When unlocking a spinlock, we require the following, strictly ordered
sequence of events:
<barrier> /* dmb */
<unlock>
<barrier> /* dsb */
<sev>
Whilst the code does indeed reflect this in terms of the architecture,
the final <barrier> + <sev> have been contracted into a single inline
asm without a "memory" clobber, therefore the compiler is at liberty to
reorder the unlock to the end of the above sequence. In such a case,
a waiting CPU may be woken up before the lock has been unlocked, leading
to extremely poor performance.
This patch reworks the dsb_sev() function to make use of the dsb()
macro and ensure ordering against the unlock.
Reported-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm/include/asm/spinlock.h | 15 +++------------
1 file changed, 3 insertions(+), 12 deletions(-)
--- a/arch/arm/include/asm/spinlock.h
+++ b/arch/arm/include/asm/spinlock.h
@@ -37,18 +37,9 @@
static inline void dsb_sev(void)
{
-#if __LINUX_ARM_ARCH__ >= 7
- __asm__ __volatile__ (
- "dsb ishst\n"
- SEV
- );
-#else
- __asm__ __volatile__ (
- "mcr p15, 0, %0, c7, c10, 4\n"
- SEV
- : : "r" (0)
- );
-#endif
+
+ dsb(ishst);
+ __asm__(SEV);
}
/*
Patches currently in stable-queue which might be from will.deacon@xxxxxxx are
queue-3.13/arm-7953-1-mm-ensure-tlb-invalidation-is-complete-before-enabling-mmu.patch
queue-3.13/arm-7955-1-spinlock-ensure-we-have-a-compiler-barrier-before-sev.patch
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