[RFC PATCH 3/7] introduce _fail variants of stop_machine functions

[Marcelo Tosatti <mtosatti@redhat.com>]

Introduce stop_machine_fail and stop_machine_cpuslocked_fail,
which check if any online CPU in the system is tagged as 
a block interference CPU. 

If so, returns an error.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: linux-2.6/include/linux/stop_machine.h
===================================================================
--- linux-2.6.orig/include/linux/stop_machine.h
+++ linux-2.6/include/linux/stop_machine.h
@@ -113,6 +113,9 @@ static inline void print_stop_info(const
  */
 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus);
 
+
+int stop_machine_fail(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus);
+
 /**
  * stop_machine_cpuslocked: freeze the machine on all CPUs and run this function
  * @fn: the function to run
@@ -124,6 +127,9 @@ int stop_machine(cpu_stop_fn_t fn, void
  */
 int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus);
 
+
+int stop_machine_cpuslocked_fail(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus);
+
 /**
  * stop_core_cpuslocked: - stop all threads on just one core
  * @cpu: any cpu in the targeted core
Index: linux-2.6/kernel/stop_machine.c
===================================================================
--- linux-2.6.orig/kernel/stop_machine.c
+++ linux-2.6/kernel/stop_machine.c
@@ -22,6 +22,7 @@
 #include <linux/atomic.h>
 #include <linux/nmi.h>
 #include <linux/sched/wake_q.h>
+#include <linux/sched/isolation.h>
 
 /*
  * Structure to determine completion condition and record errors.  May
@@ -619,6 +620,17 @@ int stop_machine_cpuslocked(cpu_stop_fn_
 	return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
 }
 
+int stop_machine_cpuslocked_fail(cpu_stop_fn_t fn, void *data,
+				 const struct cpumask *cpus)
+{
+	block_interf_assert_held();
+
+	if (cpumask_intersects(block_interf_cpumask, cpu_online_mask))
+		return -EPERM;
+
+	return stop_machine_cpuslocked(fn, data, cpus);
+}
+
 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
 {
 	int ret;
@@ -631,6 +643,19 @@ int stop_machine(cpu_stop_fn_t fn, void
 }
 EXPORT_SYMBOL_GPL(stop_machine);
 
+int stop_machine_fail(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
+{
+	int ret;
+
+	/* No CPUs can come up or down during this. */
+	cpus_read_lock();
+	ret = stop_machine_cpuslocked_fail(fn, data, cpus);
+	cpus_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(stop_machine_fail);
+
+
 #ifdef CONFIG_SCHED_SMT
 int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data)
 {