linux-kernel - [PATCH v3] cpufreq: powernv: fix stack bloat and hard limit on num cpus

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Message-ID: <20191031052159.4125031-1-jhubbard@nvidia.com>
Date:   Wed, 30 Oct 2019 22:21:59 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        <linux-pm@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>
Subject: [PATCH v3] cpufreq: powernv: fix stack bloat and hard limit on num cpus

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 with a cross-compiler based on gcc 8.1.0, which I got from:
  https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/8.1.0/

The warning is due to putting 1024 bytes on the stack:

    unsigned int chip[256];

...and it's also undesirable to have a hard limit on the number of
CPUs here.

Fix both problems by dynamically allocating based on num_possible_cpus,
as recommended by Michael Ellerman.

Fixes: 053819e0bf840 ("cpufreq: powernv: Handle throttling due to Pmax capping at chip level")
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
Cc: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc: Viresh Kumar <viresh.kumar@...aro.org>
Cc: Rafael J. Wysocki <rjw@...ysocki.net>
Cc: linux-pm@...r.kernel.org
Cc: linuxppc-dev@...ts.ozlabs.org
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---

Changes since v2: applied fixes from Michael Ellerman's review:

* Changed from CONFIG_NR_CPUS to num_possible_cpus()

* Fixed up commit description: added a note about exactly which
  compiler generates the warning. And softened up wording about
  the limitation on number of CPUs.

Changes since v1: includes Viresh's review commit fixes.

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..56f4bc0d209e 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(num_possible_cpus(), sizeof(*chip), GFP_KERNEL);
+	if (!chip)
+		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