[PATCH] cpufreq: acpi-cpufreq: add NULL check for acpi_perf_data before freeing

From: Li RongQing <[email protected]>

If alloc_percpu() fails in acpi_cpufreq_early_init(), acpi_perf_data is
NULL.  Calling free_acpi_perf_data() will execute per_cpu_ptr(NULL, i),
which does not return NULL but an offset pointer.
Dereferencing ->shared_cpu_map on this invalid pointer leads to a kernel
crash.

Fix these issues by adding a NULL check at the start of
free_acpi_perf_data() and setting acpi_perf_data to NULL after freeing.

Signed-off-by: Li RongQing <[email protected]>
---
 drivers/cpufreq/acpi-cpufreq.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 87e4923..cd2ca87 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -517,11 +517,14 @@ static void free_acpi_perf_data(void)
 {
 	unsigned int i;
 
-	/* Freeing a NULL pointer is OK, and alloc_percpu zeroes. */
+	if (!acpi_perf_data)
+		return;
+
 	for_each_possible_cpu(i)
 		free_cpumask_var(per_cpu_ptr(acpi_perf_data, i)
 				 ->shared_cpu_map);
 	free_percpu(acpi_perf_data);
+	acpi_perf_data = NULL;
 }
 
 static int cpufreq_boost_down_prep(unsigned int cpu)
-- 
2.9.4