Hi,

On 12/01/16 15:04, Viresh Kumar wrote:

On 11-01-16, 17:35, Juri Lelli wrote:

quoted

cpufreq_policy_list is guarded by cpufreq_driver_lock. Add appropriate
locking assertions to check that we always access the list while holding
the associated lock.

Cc: "Rafael J. Wysocki" <redacted>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Juri Lelli <redacted>
---
 drivers/cpufreq/cpufreq.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 00a00cd..63d6efb 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c

@@ -65,6 +65,7 @@ static bool suitable_policy(struct cpufreq_policy *policy, bool active)
 static struct cpufreq_policy *next_policy(struct cpufreq_policy *policy,
 					  bool active)
 {
+	lockdep_assert_held(&cpufreq_driver_lock);
 	do {
 		policy = list_next_entry(policy, policy_list);
 

@@ -80,6 +81,7 @@ static struct cpufreq_policy *first_policy(bool active)
 {
 	struct cpufreq_policy *policy;
 
+	lockdep_assert_held(&cpufreq_driver_lock);

Because both first_policy() and next_policy() are parts of
for_each_suitable_policy() macro, checking this in first_policy() is
sufficient. next_policy() isn't designed to be used by any other code.

But next_policy is called multiple times as part of
for_each_suitable_policy().  What if someone thinks she/he can release
cpufreq_driver_lock inside for_each_(in)active_policy() loop? Not that
it makes sense, but don't you think it could happen?

quoted

 	/* No policies in the list */
 	if (list_empty(&cpufreq_policy_list))
 		return NULL;

@@ -2430,6 +2432,7 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
 	if (ret)
 		goto err_boost_unreg;
 
+	lockdep_assert_held(&cpufreq_driver_lock);

Why do you need a cpufreq_driver_lock here? And the above change
should generate a lockdep here as the lock isn't taken right now.

Because you are checking cpufreq_policy_list to see if it's empty. And
it generates a lockdep warning, yes; fixed by next patch. Maybe putting
fixes before warnings, as you are suggesting, is better.

Thanks,

- Juri

quoted

 	if (!(cpufreq_driver->flags & CPUFREQ_STICKY) &&
 	    list_empty(&cpufreq_policy_list)) {
 		/* if all ->init() calls failed, unregister */
-- 
2.2.2

-- 
viresh