Re: [PATCH][experimantal] cpufreq: governor: Use an atomic variable for synchronization

Rafael J. Wysocki
2015-12-08T13:00:53Z

On Tuesday, December 08, 2015 12:29:05 PM Viresh Kumar wrote:
> On 08-12-15, 01:39, Rafael J. Wysocki wrote:
> > @@ -269,9 +259,6 @@ static void dbs_timer_handler(unsigned l
> > {
> > struct cpu_dbs_info *cdbs = (struct cpu_dbs_info *)data;
> > struct cpu_common_dbs_info *shared = cdbs->shared;
> > - unsigned long flags;
> > -
> > - spin_lock_irqsave(&shared->timer_lock, flags);
> >
> > /*
> > * Timer handler isn't allowed to queue work at the moment, because:
> > @@ -279,12 +266,10 @@ static void dbs_timer_handler(unsigned l
> > * - We are stopping the governor
> > * - Or we are updating the sampling rate of ondemand governor
> > */
> > - if (!shared->skip_work) {
> > - shared->skip_work++;
> > + if (atomic_inc_return(&shared->skip_work) > 1)
> > + atomic_dec(&shared->skip_work);
> > + else
> > queue_work(system_wq, &shared->work);
> > - }
>
> As explained in the other email, this is wrong..

OK, but instead of relying on the spinlock to wait for the already running
dbs_timer_handler() in gov_cancel_work() (which is really easy to overlook
and should at least be mentioned in a comment) we can wait for it explicitly.

That is, if the relevant code in gov_cancel_work() is like this:

atomic_inc(&shared->skip_work);
gov_cancel_timers(shared->policy);
cancel_work_sync(&shared->work);
gov_cancel_timers(shared->policy);
atomic_set(&shared->skip_work, 0);

then the work item should not be leaked behind the cancel_work_sync() any more
AFAICS.

Thanks,
Rafael