On Fri, Jul 13, 2012 at 08:59:39AM +0100, Shawn Guo wrote:

quoted

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 8f46446..7babc3f 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c

@@ -590,7 +590,8 @@ void smp_send_stop(void)
 
 	cpumask_copy(&mask, cpu_online_mask);
 	cpumask_clear_cpu(smp_processor_id(), &mask);
-	smp_cross_call(&mask, IPI_CPU_STOP);
+	if (!cpumask_empty(&mask))
+		smp_cross_call(&mask, IPI_CPU_STOP);

I wonder whether we shouldn't have a default smp_cross_call implementation
with BUG_ON(!cpumask_empty(&mask)). It's marginally nicer than an explicit NULL
deference and it would also fix your problem.

Will