[PATCH] cpufreq: ondemand: update sampling rate only on right CPUs

From: Fabio Baltieri
Date: Mon Nov 26 2012 - 13:11:07 EST


Fix cpufreq_gov_ondemand to skip CPU where another governor is used.

The bug present itself as NULL pointer access on the mutex_lock() call,
an can be reproduced on an SMP machine by setting the default governor
to anything other than ondemand, setting a single CPU's governor to
ondemand, then changing the sample rate by writing on:

> /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate

Backtrace:

Nov 26 17:36:54 balto kernel: [ 839.585241] BUG: unable to handle kernel NULL pointer dereference at (null)
Nov 26 17:36:54 balto kernel: [ 839.585311] IP: [<ffffffff8174e082>] __mutex_lock_slowpath+0xb2/0x170
[snip]
Nov 26 17:36:54 balto kernel: [ 839.587005] Call Trace:
Nov 26 17:36:54 balto kernel: [ 839.587030] [<ffffffff8174da82>] mutex_lock+0x22/0x40
Nov 26 17:36:54 balto kernel: [ 839.587067] [<ffffffff81610b8f>] store_sampling_rate+0xbf/0x150
Nov 26 17:36:54 balto kernel: [ 839.587110] [<ffffffff81031e9c>] ? __do_page_fault+0x1cc/0x4c0
Nov 26 17:36:54 balto kernel: [ 839.587153] [<ffffffff813309bf>] kobj_attr_store+0xf/0x20
Nov 26 17:36:54 balto kernel: [ 839.587192] [<ffffffff811bb62d>] sysfs_write_file+0xcd/0x140
Nov 26 17:36:54 balto kernel: [ 839.587234] [<ffffffff8114c12c>] vfs_write+0xac/0x180
Nov 26 17:36:54 balto kernel: [ 839.587271] [<ffffffff8114c472>] sys_write+0x52/0xa0
Nov 26 17:36:54 balto kernel: [ 839.587306] [<ffffffff810321ce>] ? do_page_fault+0xe/0x10
Nov 26 17:36:54 balto kernel: [ 839.587345] [<ffffffff81751202>] system_call_fastpath+0x16/0x1b

Signed-off-by: Fabio Baltieri <fabio.baltieri@xxxxxxxxxx>
---

Hi Rafael,

this is based on a clean linux-pm linux-next branch (i.e. not with my other
patch-set applied), so expect a context conflict if both are applied.

Thanks,
Fabio

drivers/cpufreq/cpufreq_ondemand.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index cca3e9f..7731f7c 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -40,6 +40,10 @@
static struct dbs_data od_dbs_data;
static DEFINE_PER_CPU(struct od_cpu_dbs_info_s, od_cpu_dbs_info);

+#ifndef CONFIG_CPU_FREQ_DEFAULT_GOV_ONDEMAND
+static struct cpufreq_governor cpufreq_gov_ondemand;
+#endif
+
static struct od_dbs_tuners od_tuners = {
.up_threshold = DEF_FREQUENCY_UP_THRESHOLD,
.sampling_down_factor = DEF_SAMPLING_DOWN_FACTOR,
@@ -279,6 +283,10 @@ static void update_sampling_rate(unsigned int new_rate)
policy = cpufreq_cpu_get(cpu);
if (!policy)
continue;
+ if (policy->governor != &cpufreq_gov_ondemand) {
+ cpufreq_cpu_put(policy);
+ continue;
+ }
dbs_info = &per_cpu(od_cpu_dbs_info, policy->cpu);
cpufreq_cpu_put(policy);

--
1.7.12.1

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