[PATCH 8/8] cpufreq: Nest down_write/read(cpufreq_rwsem) within get_online_cpus()/put_online_cpus()

Gautham R Shenoy
2008-04-29T13:05:32Z

cpufreq: Nest down_write/read(cpufreq_rwsem) with get_online_cpus()

From: Gautham R Shenoy <ego@in.ibm.com>

On the CPU-Hotplug callback path, the cpufreq_rwsem has a dependency
with the cpu_hotplug lock. However on the read-path, this dependency is not
honoured resulting in a possible deadlock when one tries to change
the cpufreq governor when a CPU-Hotplug is in progress.

This patch nests the down_write/read(cpufreq_rwsem) with
get_online_cpus()/put_online_cpus() pair.

Also, it introduces a try_get_online_cpus() in the do_dbs_timer() work-item
code, since we cannot do get_online_cpus() from within work items.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
---

drivers/cpufreq/cpufreq.c | 11 +++++++++--
drivers/cpufreq/cpufreq_ondemand.c | 9 +++++++--
2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 35a26a3..087f8fc 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -71,11 +71,12 @@ int lock_policy_rwsem_##mode \
{ \
int policy_cpu = per_cpu(policy_cpu, cpu); \
BUG_ON(policy_cpu == -1); \
- down_##mode(&per_cpu(cpu_policy_rwsem, policy_cpu)); \
+ get_online_cpus(); \
if (unlikely(!cpu_online(cpu))) { \
- up_##mode(&per_cpu(cpu_policy_rwsem, policy_cpu)); \
+ put_online_cpus(); \
return -1; \
} \
+ down_##mode(&per_cpu(cpu_policy_rwsem, policy_cpu)); \
\
return 0; \
}
@@ -91,6 +92,7 @@ void unlock_policy_rwsem_read(int cpu)
int policy_cpu = per_cpu(policy_cpu, cpu);
BUG_ON(policy_cpu == -1);
up_read(&per_cpu(cpu_policy_rwsem, policy_cpu));
+ put_online_cpus();
}
EXPORT_SYMBOL_GPL(unlock_policy_rwsem_read);

@@ -99,6 +101,7 @@ void unlock_policy_rwsem_write(int cpu)
int policy_cpu = per_cpu(policy_cpu, cpu);
BUG_ON(policy_cpu == -1);
up_write(&per_cpu(cpu_policy_rwsem, policy_cpu));
+ put_online_cpus();
}
EXPORT_SYMBOL_GPL(unlock_policy_rwsem_write);

@@ -1818,7 +1821,9 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
cpufreq_driver = driver_data;
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);

+ get_online_cpus();
ret = sysdev_driver_register(&cpu_sysdev_class,&cpufreq_sysdev_driver);
+ put_online_cpus();

if ((!ret) && !(cpufreq_driver->flags & CPUFREQ_STICKY)) {
int i;
@@ -1833,8 +1838,10 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
if (ret) {
dprintk("no CPU initialized for driver %s\n",
driver_data->name);
+ get_online_cpus();
sysdev_driver_unregister(&cpu_sysdev_class,
&cpufreq_sysdev_driver);
+ put_online_cpus();

spin_lock_irqsave(&cpufreq_driver_lock, flags);
cpufreq_driver = NULL;
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index d2af20d..9428f7e 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -446,12 +446,15 @@ static void do_dbs_timer(struct work_struct *work)

delay -= jiffies % delay;

- if (lock_policy_rwsem_write(cpu) < 0)
+ if (!try_get_online_cpus())
return;

+ if (lock_policy_rwsem_write(cpu) < 0)
+ goto out;
+
if (!dbs_info->enable) {
unlock_policy_rwsem_write(cpu);
- return;
+ goto out;
}

/* Common NORMAL_SAMPLE setup */
@@ -471,6 +474,8 @@ static void do_dbs_timer(struct work_struct *work)
}
queue_delayed_work_on(cpu, kondemand_wq, &dbs_info->work, delay);
unlock_policy_rwsem_write(cpu);
+out:
+ put_online_cpus();
}

static inline void dbs_timer_init(struct cpu_dbs_info_s *dbs_info)
--
Thanks and Regards
gautham