| Message ID | 1452533760-13787-6-git-send-email-juri.lelli@arm.com (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
On 11-01-16, 17:35, Juri Lelli wrote: > 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" <rjw@rjwysocki.net> > Cc: Viresh Kumar <viresh.kumar@linaro.org> > Signed-off-by: Juri Lelli <juri.lelli@arm.com> > --- > 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. > /* 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. > if (!(cpufreq_driver->flags & CPUFREQ_STICKY) && > list_empty(&cpufreq_policy_list)) { > /* if all ->init() calls failed, unregister */ > -- > 2.2.2
Hi, On 12/01/16 15:04, Viresh Kumar wrote: > On 11-01-16, 17:35, Juri Lelli wrote: > > 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" <rjw@rjwysocki.net> > > Cc: Viresh Kumar <viresh.kumar@linaro.org> > > Signed-off-by: Juri Lelli <juri.lelli@arm.com> > > --- > > 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? > > /* 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 > > if (!(cpufreq_driver->flags & CPUFREQ_STICKY) && > > list_empty(&cpufreq_policy_list)) { > > /* if all ->init() calls failed, unregister */ > > -- > > 2.2.2 > > -- > viresh > -- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 12-01-16, 11:44, Juri Lelli wrote: > 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? Okay, I don't have strong opinion about using that only in the first routine. No issues. > > > /* 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. Well, locking isn't required because we think we need to protect every access of a variable (like cpufreq_policy_list here). But we need to protect its access from possible races. What I am saying is, we can't have a race here. And so no need to lock it down.
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); /* 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); if (!(cpufreq_driver->flags & CPUFREQ_STICKY) && list_empty(&cpufreq_policy_list)) { /* if all ->init() calls failed, unregister */
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" <rjw@rjwysocki.net> Cc: Viresh Kumar <viresh.kumar@linaro.org> Signed-off-by: Juri Lelli <juri.lelli@arm.com> --- drivers/cpufreq/cpufreq.c | 3 +++ 1 file changed, 3 insertions(+)