Messages in this thread | | | Date | Tue, 12 Jan 2016 11:44:54 +0000 | From | Juri Lelli <> | Subject | Re: [RFC PATCH 05/19] cpufreq: assert locking when accessing cpufreq_policy_list |
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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 >
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