On Wednesday 24 Jun 2020 at 14:51:04 (+0200), Rafael J. Wysocki wrote: > On Wed, Jun 24, 2020 at 7:50 AM Viresh Kumar <[email protected]> wrote: > > > @@ -2789,7 +2796,13 @@ static int __init cpufreq_core_init(void) > > > cpufreq_global_kobject = kobject_create_and_add("cpufreq", > > > &cpu_subsys.dev_root->kobj); > > > BUG_ON(!cpufreq_global_kobject); > > > > > > + mutex_lock(&cpufreq_governor_mutex); > > > + if (!default_governor) > > > + default_governor = cpufreq_default_governor(); > > > + mutex_unlock(&cpufreq_governor_mutex); > > > > I don't think locking is required here at core-initcall level. > > It isn't necessary AFAICS, but it may as well be regarded as > annotation (kind of instead of having a comment explaining why it need > not be used).
Right, but I must admit that, looking at this more, I'm getting a bit confused with the overall locking for governors :/ When in cpufreq_init_policy() we find a governor using find_governor(policy->last_governor), what guarantees this governor is not concurrently unregistered? That is, what guarantees this governor doesn't go away between that find_governor() call, and the subsequent call to try_module_get() in cpufreq_set_policy() down the line? Can we somewhat assume that whatever governor is referred to by policy->last_governor will have a non-null refcount? Or are the cpufreq_online() and cpufreq_unregister_governor() path mutually exclusive? Or is there something else? Thanks, Quentin
