[RFC PATCH 2/7] introduce smp_call_func_single_fail

[Marcelo Tosatti <mtosatti@redhat.com>]

Introduce smp_call_func_single_fail, which checks if
the target CPU is tagged as a "block interference" CPU,
and returns an error if so.

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

Index: linux-2.6/include/linux/smp.h
===================================================================
--- linux-2.6.orig/include/linux/smp.h
+++ linux-2.6/include/linux/smp.h
@@ -50,6 +50,9 @@ extern unsigned int total_cpus;
 int smp_call_function_single(int cpuid, smp_call_func_t func, void *info,
 			     int wait);
 
+int smp_call_func_single_fail(int cpuid, smp_call_func_t func, void *info,
+			     int wait);
+
 void on_each_cpu_cond_mask(smp_cond_func_t cond_func, smp_call_func_t func,
 			   void *info, bool wait, const struct cpumask *mask);
 
Index: linux-2.6/kernel/smp.c
===================================================================
--- linux-2.6.orig/kernel/smp.c
+++ linux-2.6/kernel/smp.c
@@ -25,6 +25,7 @@
 #include <linux/nmi.h>
 #include <linux/sched/debug.h>
 #include <linux/jump_label.h>
+#include <linux/sched/isolation.h>
 
 #include "smpboot.h"
 #include "sched/smp.h"
@@ -782,6 +783,30 @@ int smp_call_function_single(int cpu, sm
 }
 EXPORT_SYMBOL(smp_call_function_single);
 
+/*
+ * smp_call_func_single_fail - Run a function on a specific CPU,
+ * failing if any target CPU is marked as "no ipi".
+ * @func: The function to run. This must be fast and non-blocking.
+ * @info: An arbitrary pointer to pass to the function.
+ * @wait: If true, wait until function has completed on other CPUs.
+ *
+ * Returns 0 on success, else a negative status code.
+ */
+int smp_call_func_single_fail(int cpu, smp_call_func_t func, void *info,
+			     int wait)
+{
+	int err;
+
+	block_interf_assert_held();
+	if (block_interf_cpu(cpu))
+		return -EPERM;
+
+	err = smp_call_function_single(cpu, func, info, wait);
+
+	return err;
+}
+EXPORT_SYMBOL(smp_call_func_single_fail);
+
 /**
  * smp_call_function_single_async() - Run an asynchronous function on a
  * 			         specific CPU.