From e71f5cc402ecb42b407ae52add7b173bf1c53daa Mon Sep 17 00:00:00 2001
From: Naga Chumbalkar <nagananda.chumbalkar@hp.com>
Date: Wed, 14 Sep 2011 16:22:23 -0700
Subject: [PATCH] drivers/cpufreq/pcc-cpufreq.c: avoid NULL pointer dereference

per_cpu(processors, n) can be NULL, resulting in:

  Loading CPUFreq modules[  437.661360] BUG: unable to handle kernel NULL pointer dereference at (null)
  IP: [<ffffffffa0434314>] pcc_cpufreq_cpu_init+0x74/0x220 [pcc_cpufreq]

It's better to avoid the oops by failing the driver, and allowing the
system to boot.

Signed-off-by: Naga Chumbalkar <nagananda.chumbalkar@hp.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Len Brown <lenb@kernel.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
 drivers/cpufreq/pcc-cpufreq.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/cpufreq/pcc-cpufreq.c b/drivers/cpufreq/pcc-cpufreq.c
index 7b0603eb0129..cdc02ac8f41a 100644
--- a/drivers/cpufreq/pcc-cpufreq.c
+++ b/drivers/cpufreq/pcc-cpufreq.c
@@ -261,6 +261,9 @@ static int pcc_get_offset(int cpu)
 	pr = per_cpu(processors, cpu);
 	pcc_cpu_data = per_cpu_ptr(pcc_cpu_info, cpu);
 
+	if (!pr)
+		return -ENODEV;
+
 	status = acpi_evaluate_object(pr->handle, "PCCP", NULL, &buffer);
 	if (ACPI_FAILURE(status))
 		return -ENODEV;
-- 
2.20.1