commit 23fbd28362ceb22ee2fb3bab899dda6bac129263
Author: Andriy Gapon <avg@icyb.net.ua>
Date:   Fri Jul 6 20:17:03 2012 +0300

    acpi_cpu: add a safe way of disabling acpi_cpu_idle method
    
    the new way ensures that there are no CPUs in the idle method after
    disable_idle() is executed

diff --git a/sys/dev/acpica/acpi_cpu.c b/sys/dev/acpica/acpi_cpu.c
index 5aa4097..16445a8 100644
--- a/sys/dev/acpica/acpi_cpu.c
+++ b/sys/dev/acpica/acpi_cpu.c
@@ -139,6 +139,8 @@ static int		 cpu_quirks;	/* Indicate any hardware bugs. */
 
 /* Runtime state. */
 static int		 cpu_disable_idle; /* Disable entry to idle function */
+static struct mtx	 cpu_disable_idle_lock;
+MTX_SYSINIT(cpu_disable_idle, &cpu_disable_idle_lock, "cpuidle lock", MTX_SPIN);
 
 /* Values for sysctl. */
 static struct sysctl_ctx_list cpu_sysctl_ctx;
@@ -418,6 +420,42 @@ acpi_cpu_postattach(void *unused __unused)
 SYSINIT(acpi_cpu, SI_SUB_CONFIGURE, SI_ORDER_MIDDLE,
     acpi_cpu_postattach, NULL);
 
+static void
+disable_idle(void)
+{
+    mtx_lock_spin(&cpu_disable_idle_lock);
+    cpu_disable_idle = TRUE;
+    mtx_unlock_spin(&cpu_disable_idle_lock);
+
+    /*
+     * Ensure that no CPU is in idle state or in acpi_cpu_idle().
+     * Note that this code depends on the fact that the rendezvous IPI
+     * can not penetrate context where interrupts are disabled and acpi_cpu_idle
+     * is called and executed in such a context, interrupts are re-enabled
+     * right before return.
+     */
+    smp_rendezvous(smp_no_rendevous_barrier, NULL, smp_no_rendevous_barrier, NULL);
+}
+
+static void
+enable_idle(void)
+{
+    mtx_lock_spin(&cpu_disable_idle_lock);
+    cpu_disable_idle = FALSE;
+    mtx_unlock_spin(&cpu_disable_idle_lock);
+}
+
+static int
+is_idle_disabled(void)
+{
+    int ret;
+
+    mtx_lock_spin(&cpu_disable_idle_lock);
+    ret = cpu_disable_idle;
+    mtx_unlock_spin(&cpu_disable_idle_lock);
+    return (ret);
+}
+
 /*
  * Disable any entry to the idle function during suspend and re-enable it
  * during resume.
@@ -430,7 +468,7 @@ acpi_cpu_suspend(device_t dev)
     error = bus_generic_suspend(dev);
     if (error)
 	return (error);
-    cpu_disable_idle = TRUE;
+    disable_idle();
     return (0);
 }
 
@@ -438,7 +476,7 @@ static int
 acpi_cpu_resume(device_t dev)
 {
 
-    cpu_disable_idle = FALSE;
+    enable_idle();
     return (bus_generic_resume(dev));
 }
 
@@ -572,12 +610,13 @@ acpi_cpu_shutdown(device_t dev)
     bus_generic_shutdown(dev);
 
     /*
-     * Disable any entry to the idle function.  There is a small race where
-     * an idle thread have passed this check but not gone to sleep.  This
-     * is ok since device_shutdown() does not free the softc, otherwise
-     * we'd have to be sure all threads were evicted before returning.
+     * Disable any entry to the idle function.
+     */
+    disable_idle();
+
+    /*
+     * TODO: properly free all resources.
      */
-    cpu_disable_idle = TRUE;
 
     return_VALUE (0);
 }
@@ -860,7 +899,7 @@ acpi_cpu_startup(void *arg)
 
     /* Take over idling from cpu_idle_default(). */
     cpu_cx_lowest_lim = 0;
-    cpu_disable_idle = FALSE;
+    enable_idle();
     cpu_idle_hook = acpi_cpu_idle;
 }
 
@@ -925,7 +964,7 @@ acpi_cpu_idle()
     int		bm_active, cx_next_idx, i;
 
     /* If disabled, return immediately. */
-    if (cpu_disable_idle) {
+    if (is_idle_disabled()) {
 	ACPI_ENABLE_IRQS();
 	return;
     }