[PATCH] ARM: change definition of cpu_relax() for ARM11MPCore
Will Deacon
will.deacon at arm.com
Thu May 27 11:11:58 EDT 2010
The cpu_relax() macro is often used in the body of busy-wait loops to ensure
that the variable being spun on is re-loaded for each iteration. On the
ARM11MPCore processor [where loads are prioritised over stores], spinning in
such a loop will prevent the write buffer from draining. If a write contained
in the write buffer indirectly affects the variable being spun on, there is a
potential for deadlock. This deadlock is experienced when executing the KGDB
testsuite on an SMP ARM11MPCore configuration.
This patch changes the definition of cpu_relax() to smp_mb() for ARMv6 cores,
forcing a flushing of the write buffer on SMP systems before the next load
takes place. If the Kernel is not compiled for SMP support, this will expand
to a barrier() as before.
Cc: Russell King - ARM Linux <linux at arm.linux.org.uk>
Acked-by: Catalin Marinas <catalin.marinas at arm.com>
Signed-off-by: Will Deacon <will.deacon at arm.com>
---
Russell - the discussion on this last month seemed to draw to a close.
Can I submit this to the patch system please, or are there any outstanding
issues?
arch/arm/include/asm/processor.h | 4 ++++
1 files changed, 4 insertions(+), 0 deletions(-)
diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h
index 6a89567..7bed3da 100644
--- a/arch/arm/include/asm/processor.h
+++ b/arch/arm/include/asm/processor.h
@@ -91,7 +91,11 @@ extern void release_thread(struct task_struct *);
unsigned long get_wchan(struct task_struct *p);
+#if __LINUX_ARM_ARCH__ == 6
+#define cpu_relax() smp_mb()
+#else
#define cpu_relax() barrier()
+#endif
/*
* Create a new kernel thread
--
1.6.3.3
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