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Subject[PATCH] cpufreq: powernv: fix stack bloat and NR_CPUS limitation
Date
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.bhat@linux.vnet.ibm.com>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: linux-pm@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: John Hubbard <jhubbard@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
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