ACPI/CPUIDLE: prevent setting pm_idle to NULL

pm_idle_save resp. pm_idle_old can be NULL when the restore code in
acpi_processor_cst_has_changed() resp. cpuidle_uninstall_idle_handler()
is called. This can set pm_idle unconditinally to NULL, which causes the
kernel to panic when calling pm_idle in the x86 idle code. This was
covered by an extra check for !pm_idle in the x86 idle code, which was
removed during the x86 idle code refactoring.

Instead of restoring the pm_idle check in the x86 code prevent the
acpi/cpuidle code to set pm_idle to NULL.

Reported by: Dhaval Giani http://lkml.org/lkml/2008/7/2/309
Based on a debug patch from Ingo Molnar

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 12 insertions, 5 deletions

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index b7f2963693a7..283c08f5f4d4 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -1332,9 +1332,15 @@ int acpi_processor_cst_has_changed(struct acpi_processor *pr)
         if (!pr->flags.power_setup_done)
                 return -ENODEV;
 
-        /* Fall back to the default idle loop */
-        pm_idle = pm_idle_save;
-        synchronize_sched();    /* Relies on interrupts forcing exit from idle. */
+        /*
+         * Fall back to the default idle loop, when pm_idle_save had
+         * been initialized.
+         */
+        if (pm_idle_save) {
+                pm_idle = pm_idle_save;
+                /* Relies on interrupts forcing exit from idle. */
+                synchronize_sched();
+        }
 
         pr->flags.power = 0;
         result = acpi_processor_get_power_info(pr);
@@ -1896,7 +1902,8 @@ int acpi_processor_power_exit(struct acpi_processor *pr,
 
         /* Unregister the idle handler when processor #0 is removed. */
         if (pr->id == 0) {
-                pm_idle = pm_idle_save;
+                if (pm_idle_save)
+                        pm_idle = pm_idle_save;
 
                 /*
                  * We are about to unload the current idle thread pm callback
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 5405769020a1..5ce07b517c58 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -94,7 +94,7 @@ void cpuidle_install_idle_handler(void)
  */
 void cpuidle_uninstall_idle_handler(void)
 {
-        if (enabled_devices && (pm_idle != pm_idle_old)) {
+        if (enabled_devices && pm_idle_old && (pm_idle != pm_idle_old)) {
                 pm_idle = pm_idle_old;
                 cpuidle_kick_cpus();
         }