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Subject[PATCH V3 3/5] cpufreq: governor: Avoid invalid states with additional checks
Date
There can be races where the request has come to a wrong state. For
example INIT followed by STOP (instead of START) or START followed by
EXIT (instead of STOP).

Tackle these races by comparing making sure the state-machine never gets
into any invalid state. And return error if an invalid state-transition
is requested.

Reviewed-and-tested-by: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
---
drivers/cpufreq/cpufreq_governor.c | 46 +++++++++++++++++++++++++++++---------
1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 7ed0ec2ac853..f225dc975415 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -305,6 +305,10 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy,
unsigned int latency;
int ret;

+ /* State should be equivalent to EXIT */
+ if (policy->governor_data)
+ return -EBUSY;
+
if (dbs_data) {
if (WARN_ON(have_governor_per_policy()))
return -EINVAL;
@@ -375,10 +379,15 @@ static int cpufreq_governor_init(struct cpufreq_policy *policy,
return ret;
}

-static void cpufreq_governor_exit(struct cpufreq_policy *policy,
- struct dbs_data *dbs_data)
+static int cpufreq_governor_exit(struct cpufreq_policy *policy,
+ struct dbs_data *dbs_data)
{
struct common_dbs_data *cdata = dbs_data->cdata;
+ struct cpu_dbs_info *cdbs = cdata->get_cpu_cdbs(policy->cpu);
+
+ /* State should be equivalent to INIT */
+ if (!cdbs->shared || cdbs->shared->policy)
+ return -EBUSY;

policy->governor_data = NULL;
if (!--dbs_data->usage_count) {
@@ -395,6 +404,7 @@ static void cpufreq_governor_exit(struct cpufreq_policy *policy,
}

free_common_dbs_info(policy, cdata);
+ return 0;
}

static int cpufreq_governor_start(struct cpufreq_policy *policy,
@@ -409,6 +419,10 @@ static int cpufreq_governor_start(struct cpufreq_policy *policy,
if (!policy->cur)
return -EINVAL;

+ /* State should be equivalent to INIT */
+ if (!shared || shared->policy)
+ return -EBUSY;
+
if (cdata->governor == GOV_CONSERVATIVE) {
struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;

@@ -465,14 +479,18 @@ static int cpufreq_governor_start(struct cpufreq_policy *policy,
return 0;
}

-static void cpufreq_governor_stop(struct cpufreq_policy *policy,
- struct dbs_data *dbs_data)
+static int cpufreq_governor_stop(struct cpufreq_policy *policy,
+ struct dbs_data *dbs_data)
{
struct common_dbs_data *cdata = dbs_data->cdata;
unsigned int cpu = policy->cpu;
struct cpu_dbs_info *cdbs = cdata->get_cpu_cdbs(cpu);
struct cpu_common_dbs_info *shared = cdbs->shared;

+ /* State should be equivalent to START */
+ if (!shared || !shared->policy)
+ return -EBUSY;
+
gov_cancel_work(dbs_data, policy);

if (cdata->governor == GOV_CONSERVATIVE) {
@@ -484,17 +502,19 @@ static void cpufreq_governor_stop(struct cpufreq_policy *policy,

shared->policy = NULL;
mutex_destroy(&shared->timer_mutex);
+ return 0;
}

-static void cpufreq_governor_limits(struct cpufreq_policy *policy,
- struct dbs_data *dbs_data)
+static int cpufreq_governor_limits(struct cpufreq_policy *policy,
+ struct dbs_data *dbs_data)
{
struct common_dbs_data *cdata = dbs_data->cdata;
unsigned int cpu = policy->cpu;
struct cpu_dbs_info *cdbs = cdata->get_cpu_cdbs(cpu);

+ /* State should be equivalent to START */
if (!cdbs->shared || !cdbs->shared->policy)
- return;
+ return -EBUSY;

mutex_lock(&cdbs->shared->timer_mutex);
if (policy->max < cdbs->shared->policy->cur)
@@ -505,13 +525,15 @@ static void cpufreq_governor_limits(struct cpufreq_policy *policy,
CPUFREQ_RELATION_L);
dbs_check_cpu(dbs_data, cpu);
mutex_unlock(&cdbs->shared->timer_mutex);
+
+ return 0;
}

int cpufreq_governor_dbs(struct cpufreq_policy *policy,
struct common_dbs_data *cdata, unsigned int event)
{
struct dbs_data *dbs_data;
- int ret = 0;
+ int ret;

/* Lock governor to block concurrent initialization of governor */
mutex_lock(&cdata->mutex);
@@ -531,17 +553,19 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
ret = cpufreq_governor_init(policy, dbs_data, cdata);
break;
case CPUFREQ_GOV_POLICY_EXIT:
- cpufreq_governor_exit(policy, dbs_data);
+ ret = cpufreq_governor_exit(policy, dbs_data);
break;
case CPUFREQ_GOV_START:
ret = cpufreq_governor_start(policy, dbs_data);
break;
case CPUFREQ_GOV_STOP:
- cpufreq_governor_stop(policy, dbs_data);
+ ret = cpufreq_governor_stop(policy, dbs_data);
break;
case CPUFREQ_GOV_LIMITS:
- cpufreq_governor_limits(policy, dbs_data);
+ ret = cpufreq_governor_limits(policy, dbs_data);
break;
+ default:
+ ret = -EINVAL;
}

unlock:
--
2.4.0


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