ARM: SMP: ensure smp_send_stop() waits for CPUs to stop

Wait for CPUs to indicate that they've stopped, after sending the
stop IPI, rather than blindly continuing on and hoping that they've
stopped in time.  Print a warning if we fail to stop the other CPUs.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 15 insertions, 3 deletions

diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 1de3e13a42a1..64f2d198c764 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -575,10 +575,22 @@ void smp_send_reschedule(int cpu)
 
 void smp_send_stop(void)
 {
-        cpumask_t mask = cpu_online_map;
-        cpu_clear(smp_processor_id(), mask);
-        if (!cpus_empty(mask))
+        unsigned long timeout;
+
+        if (num_online_cpus() > 1) {
+                cpumask_t mask = cpu_online_map;
+                cpu_clear(smp_processor_id(), mask);
+
                 smp_cross_call(&mask, IPI_CPU_STOP);
+        }
+
+        /* Wait up to one second for other CPUs to stop */
+        timeout = USEC_PER_SEC;
+        while (num_online_cpus() > 1 && timeout--)
+                udelay(1);
+
+        if (num_online_cpus() > 1)
+                pr_warning("SMP: failed to stop secondary CPUs\n");
 }
 
 /*