[PATCH] cpufreq: powernv: fix stack bloat and NR_CPUS limitation

[John Hubbard]

The following build warning occurred on powerpc 64-bit builds:

drivers/cpufreq/powernv-cpufreq.c: In function 'init_chip_info':
drivers/cpufreq/powernv-cpufreq.c:1070:1: warning: the frame size of 1040 bytes 
is larger than 1024 bytes [-Wframe-larger-than=]

This is due to putting 1024 bytes on the stack:

    unsigned int chip[256];

...and while looking at this, it also has a bug: it fails with a stack
overrun, if CONFIG_NR_CPUS > 256.

Fix both problems by dynamically allocating based on CONFIG_NR_CPUS.

Fixes: 053819e0bf840 ("cpufreq: powernv: Handle throttling due to Pmax capping 
at chip level")
Cc: Shilpasri G Bhat <shilpa.b...@linux.vnet.ibm.com>
Cc: Preeti U Murthy <pre...@linux.vnet.ibm.com>
Cc: Viresh Kumar <viresh.ku...@linaro.org>
Cc: Rafael J. Wysocki <r...@rjwysocki.net>
Cc: linux...@vger.kernel.org
Cc: linuxppc-...@lists.ozlabs.org
Signed-off-by: John Hubbard <jhubb...@nvidia.com>
---

Hi,

I have only compile-tested this, so I would appreciate if anyone
could do a basic runtime test on it. But (famous last words) it
seems simple enough that I'm confident it's correct. oh boy. :)

thanks,
John Hubbard
NVIDIA

 drivers/cpufreq/powernv-cpufreq.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/powernv-cpufreq.c 
b/drivers/cpufreq/powernv-cpufreq.c
index 6061850e59c9..78e04402125f 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -1041,9 +1041,14 @@ static struct cpufreq_driver powernv_cpufreq_driver = {
 
 static int init_chip_info(void)
 {
-       unsigned int chip[256];
+       unsigned int *chip;
        unsigned int cpu, i;
        unsigned int prev_chip_id = UINT_MAX;
+       int ret = 0;
+
+       chip = kcalloc(CONFIG_NR_CPUS, sizeof(int), GFP_KERNEL);
+       if (!chips)
+               return -ENOMEM;
 
        for_each_possible_cpu(cpu) {
                unsigned int id = cpu_to_chip_id(cpu);
@@ -1055,8 +1060,10 @@ static int init_chip_info(void)
        }
 
        chips = kcalloc(nr_chips, sizeof(struct chip), GFP_KERNEL);
-       if (!chips)
-               return -ENOMEM;
+       if (!chips) {
+               ret = -ENOMEM;
+               goto free_and_return;
+       }
 
        for (i = 0; i < nr_chips; i++) {
                chips[i].id = chip[i];
@@ -1066,7 +1073,9 @@ static int init_chip_info(void)
                        per_cpu(chip_info, cpu) =  &chips[i];
        }
 
-       return 0;
+free_and_return:
+       kfree(chip);
+       return ret;
 }
 
 static inline void clean_chip_info(void)
-- 
2.23.0