Messages in this thread | | | From | Dmitry Torokhov <> | Subject | Re: [PATCH 3/4] PM / OPP: take RCU lock in dev_pm_opp_get_opp_count | Date | Wed, 17 Dec 2014 09:28:42 -0800 |
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On Wednesday, December 17, 2014 10:06:17 AM Viresh Kumar wrote: > On 17 December 2014 at 04:39, Dmitry Torokhov <dtor@chromium.org> wrote: > > A lot of callers are missing the fact that dev_pm_opp_get_opp_count > > needs to be called under RCU lock. Given that RCU locks can safely be > > nested, instead of providing *_locked() API, let's take RCU lock inside > > Hmm, I asked for a *_locked() API because many users of > dev_pm_opp_get_opp_count() are already calling it from rcu read side > critical sections. > > Now, there are two questions: > - Can rcu-read side critical sections be nested ? > > Yes, this is what the comment over rcu_read_lock() says > > * RCU read-side critical sections may be nested. Any deferred actions > * will be deferred until the outermost RCU read-side critical section > * completes. > > - Would it be better to drop these double rcu_read_locks() ? i.e. either > get a *_locked() API or fix the callers of dev_pm_opp_get_opp_count(). > > @Paul: What do you say ? >
FWIW the change is a stop-gap; I hope we'll get away from using dev_pm_opp_get_opp_count() in cpufreq drivers and then we can revert the change. I just did not want to touch cpufreq drivers unless necessary.
Thanks, Dmitry
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