From: Will Deacon Date: Mon, 21 Jun 2010 14:29:03 +0000 (+0100) Subject: ARM: 6194/1: change definition of cpu_relax() for ARM11MPCore X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=534be1d5a2da940ecc5e528992ea4ace8658157a;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git ARM: 6194/1: change definition of cpu_relax() for ARM11MPCore Linux expects that if a CPU modifies a memory location, then that modification will eventually become visible to other CPUs in the system. On an ARM11MPCore processor, loads are prioritised over stores so it is possible for a store operation to be postponed if a polling loop immediately follows it. If the variable being polled indirectly depends on the outstanding store [for example, another CPU may be polling the variable that is pending modification] then there is the potential for deadlock if interrupts are disabled. This deadlock occurs in the KGDB testsuire when executing 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. Acked-by: Catalin Marinas Signed-off-by: Will Deacon Signed-off-by: Russell King --- diff --git a/arch/arm/include/asm/processor.h b/arch/arm/include/asm/processor.h index 6a89567ffc5b..7bed3daf83b8 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