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Subject[RFC, 2.6.26.2-rc1] ACPI/CPUIDLE: prevent setting pm_idle to NULL
From b032bf70df2e43149ce2b4e9a865b076c6140753 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 27 Jul 2008 23:47:12 +0200
Subject: [PATCH] ACPI/CPUIDLE: prevent setting pm_idle to NULL

[ Upstream commit b032bf70df2e43149ce2b4e9a865b076c6140753 ]

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>
CC: Oliver Pinter <oliver.pntr@gmail.com>

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index b7f2963..283c08f 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 5405769..5ce07b5 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();
}



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