[rfc] bind curthread to target cpu for _CST change notification

[Andriy Gapon]

I would like to propose the following patch which should kill two birds with one
stone:

- avoid race in acpi_cpu_cx_cst if more than one notifications occur in a rapid
succession for the same CPU and end up being concurrently handled by ACPI taskqeue
threads
- avoid race acpi_cpu_cx_cst and acpi_cpu_idle where the latter may access
resources being updated by the former

What do you think?

Index: sys/dev/acpica/acpi_cpu.c
===================================================================
--- sys/dev/acpica/acpi_cpu.c	(revision 242854)
+++ sys/dev/acpica/acpi_cpu.c	(working copy)
@@ -1047,7 +1047,16 @@
 	return;

     /* Update the list of Cx states. */
+    thread_lock(curthread);
+    sched_bind(curthread, sc->cpu_pcpu->pc_cpuid);
+    thread_unlock(curthread);
+    critical_enter();
     acpi_cpu_cx_cst(sc);
+    critical_exit();
+    thread_lock(curthread);
+    sched_unbind(curthread);
+    thread_unlock(curthread);
+
     acpi_cpu_cx_list(sc);

     ACPI_SERIAL_BEGIN(cpu);

-- 
Andriy Gapon