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authorViresh Kumar <viresh.kumar@linaro.org>2016-02-09 09:01:33 +0530
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2016-03-09 14:40:58 +0100
commitc4435630361d9bebf7154a0c842dc1fb7ae39c99 (patch)
tree6b8eeab3ceb2fa74d260708e8310990586d87f6b /drivers/cpufreq/cpufreq_governor.h
parentff4b17895e3166084c76ae703cb1c757bcc59799 (diff)
cpufreq: governor: New sysfs show/store callbacks for governor tunables
The ondemand and conservative governors use the global-attr or freq-attr structures to represent sysfs attributes corresponding to their tunables (which of them is actually used depends on whether or not different policy objects can use the same governor with different tunables at the same time and, consequently, on where those attributes are located in sysfs). Unfortunately, in the freq-attr case, the standard cpufreq show/store sysfs attribute callbacks are applied to the governor tunable attributes and they always acquire the policy->rwsem lock before carrying out the operation. That may lead to an ABBA deadlock if governor tunable attributes are removed under policy->rwsem while one of them is being accessed concurrently (if sysfs attributes removal wins the race, it will wait for the access to complete with policy->rwsem held while the attribute callback will block on policy->rwsem indefinitely). We attempted to address this issue by dropping policy->rwsem around governor tunable attributes removal (that is, around invocations of the ->governor callback with the event arg equal to CPUFREQ_GOV_POLICY_EXIT) in cpufreq_set_policy(), but that opened up race conditions that had not been possible with policy->rwsem held all the time. Therefore policy->rwsem cannot be dropped in cpufreq_set_policy() at any point, but the deadlock situation described above must be avoided too. To that end, use the observation that in principle governor tunables may be represented by the same data type regardless of whether the governor is system-wide or per-policy and introduce a new structure, struct governor_attr, for representing them and new corresponding macros for creating show/store sysfs callbacks for them. Also make their parent kobject use a new kobject type whose default show/store callbacks are not related to the standard core cpufreq ones in any way (and they don't acquire policy->rwsem in particular). Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> Tested-by: Juri Lelli <juri.lelli@arm.com> Tested-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com> [ rjw: Subject & changelog + rebase ] Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/cpufreq/cpufreq_governor.h')
-rw-r--r--drivers/cpufreq/cpufreq_governor.h39
1 files changed, 37 insertions, 2 deletions
diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
index e296362d21d2..bdb6e4940b75 100644
--- a/drivers/cpufreq/cpufreq_governor.h
+++ b/drivers/cpufreq/cpufreq_governor.h
@@ -160,8 +160,44 @@ struct dbs_data {
unsigned int sampling_rate;
unsigned int sampling_down_factor;
unsigned int up_threshold;
+
+ struct kobject kobj;
+ /* Protect concurrent updates to governor tunables from sysfs */
+ struct mutex mutex;
+};
+
+/* Governor's specific attributes */
+struct dbs_data;
+struct governor_attr {
+ struct attribute attr;
+ ssize_t (*show)(struct dbs_data *dbs_data, char *buf);
+ ssize_t (*store)(struct dbs_data *dbs_data, const char *buf,
+ size_t count);
};
+#define gov_show_one(_gov, file_name) \
+static ssize_t show_##file_name \
+(struct dbs_data *dbs_data, char *buf) \
+{ \
+ struct _gov##_dbs_tuners *tuners = dbs_data->tuners; \
+ return sprintf(buf, "%u\n", tuners->file_name); \
+}
+
+#define gov_show_one_common(file_name) \
+static ssize_t show_##file_name \
+(struct dbs_data *dbs_data, char *buf) \
+{ \
+ return sprintf(buf, "%u\n", dbs_data->file_name); \
+}
+
+#define gov_attr_ro(_name) \
+static struct governor_attr _name = \
+__ATTR(_name, 0444, show_##_name, NULL)
+
+#define gov_attr_rw(_name) \
+static struct governor_attr _name = \
+__ATTR(_name, 0644, show_##_name, store_##_name)
+
/* Common to all CPUs of a policy */
struct policy_dbs_info {
struct cpufreq_policy *policy;
@@ -236,8 +272,7 @@ struct dbs_governor {
#define GOV_ONDEMAND 0
#define GOV_CONSERVATIVE 1
int governor;
- struct attribute_group *attr_group_gov_sys; /* one governor - system */
- struct attribute_group *attr_group_gov_pol; /* one governor - policy */
+ struct kobj_type kobj_type;
/*
* Common data for platforms that don't set