3.13-stable review patch. If anyone has any objections, please let me know.
------------------
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);
}
/*
--
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