On Tue, Apr 02, 2013 at 08:29:12PM +0530, Viresh Kumar wrote:
> On 2 April 2013 20:25, Nathan Zimmer <nzimmer@xxxxxxx> wrote:
> > The lock is unneeded if we expect register and unregister driver to not be
> > called from muliple threads at once. I didn't make that assumption.
>
> Hmm.. But doesn't rcu part take care of that too?? Two writers
> updating stuff simultaneously?
My concern is in the cpufreq_register_driver. Since we are only to set the
pointer when it is null we have have to hold the lock over both operations.
int cpufreq_register_driver(struct cpufreq_driver *driver_data)
{
...
spin_lock_irqsave(&cpufreq_driver_lock, flags);
if (rcu_access_pointer(cpufreq_driver)) {
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
return -EBUSY;
}
rcu_assign_pointer(cpufreq_driver, driver_data);
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
synchronize_rcu();
...
}
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