ARM: 9317/1: kexec: Make smp stop calls asynchronous

If a panic is triggered by a hrtimer interrupt all online cpus will be
notified and set offline. But as highlighted by commit 19dbdcb8
("smp: Warn on function calls from softirq context") this call should
not be made synchronous with disabled interrupts:

 softdog: Initiating panic
 Kernel panic - not syncing: Software Watchdog Timer expired
 WARNING: CPU: 1 PID: 0 at kernel/smp.c:753 smp_call_function_many_cond
   unwind_backtrace:
     show_stack
     dump_stack_lvl
     __warn
     warn_slowpath_fmt
     smp_call_function_many_cond
     smp_call_function
     crash_smp_send_stop.part.0
     machine_crash_shutdown
     __crash_kexec
     panic
     softdog_fire
     __hrtimer_run_queues
     hrtimer_interrupt

Make the smp call for machine_crash_nonpanic_core() asynchronous.
Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

arch/arm/kernel/machine_kexec.c

@@ -94,16 +94,28 @@ static void machine_crash_nonpanic_core(void *unused)
 	}
 }
 
+static DEFINE_PER_CPU(call_single_data_t, cpu_stop_csd) =
+	CSD_INIT(machine_crash_nonpanic_core, NULL);
+
 void crash_smp_send_stop(void)
 {
 	static int cpus_stopped;
 	unsigned long msecs;
+	call_single_data_t *csd;
+	int cpu, this_cpu = raw_smp_processor_id();
 
 	if (cpus_stopped)
 		return;
 
 	atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);
-	smp_call_function(machine_crash_nonpanic_core, NULL, false);
+	for_each_online_cpu(cpu) {
+		if (cpu == this_cpu)
+			continue;
+
+		csd = &per_cpu(cpu_stop_csd, cpu);
+		smp_call_function_single_async(cpu, csd);
+	}
+
 	msecs = 1000; /* Wait at most a second for the other cpus to stop */
 	while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
 		mdelay(1);