On 26-07-17, 23:13, Joel Fernandes (Google) wrote: > On Wed, Jul 26, 2017 at 10:50 PM, Viresh Kumar <viresh.ku...@linaro.org> > wrote: > > On 26-07-17, 22:34, Joel Fernandes (Google) wrote: > >> On Wed, Jul 26, 2017 at 2:22 AM, Viresh Kumar <viresh.ku...@linaro.org> > >> wrote: > >> > @@ -221,7 +226,7 @@ static void sugov_update_single(struct > >> > update_util_data *hook, u64 time, > >> > sugov_set_iowait_boost(sg_cpu, time, flags); > >> > sg_cpu->last_update = time; > >> > > >> > - if (!sugov_should_update_freq(sg_policy, time)) > >> > + if (!sugov_should_update_freq(sg_policy, time, hook->cpu)) > >> > return; > >> > >> Since with the remote callbacks now possible, isn't it unsafe to > >> modify sg_cpu and sg_policy structures without a lock in > >> sugov_update_single? > >> > >> Unlike sugov_update_shared, we don't acquire any lock in > >> sugov_update_single before updating these structures. Did I miss > >> something? > > > > As Peter already mentioned it earlier, the callbacks are called with > > rq locks held and so sugov_update_single() wouldn't get called in > > parallel for a target CPU. > > Ah ok, I have to catch up with that discussion since I missed the > whole thing. Now that you will have me on CC, that shouldn't happen, > thanks and sorry about the noise. > > > That's the only race you were worried about ? > > Yes. So then in that case, makes sense to move raw_spin_lock in > sugov_update_shared further down? (Just discussing, this point is > independent of your patch), Something like:
Even that was discussed tomorrow with Peter :) No it wouldn't work because sg_cpu->util we are updating here may be getting read from some other cpu that shares policy with sg_cpu. -- viresh