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Date: Tue, 1 Mar 2016 13:57:27 +0100 From: Peter Zijlstra <peterz@...radead.org> To: "Rafael J. Wysocki" <rjw@...ysocki.net> Cc: Steve Muckle <steve.muckle@...aro.org>, Ingo Molnar <mingo@...hat.com>, "Rafael J. Wysocki" <rafael@...nel.org>, linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org, Vincent Guittot <vincent.guittot@...aro.org>, Morten Rasmussen <morten.rasmussen@....com>, Dietmar Eggemann <dietmar.eggemann@....com>, Juri Lelli <Juri.Lelli@....com>, Patrick Bellasi <patrick.bellasi@....com>, Michael Turquette <mturquette@...libre.com>, Ricky Liang <jcliang@...omium.org> Subject: Re: [RFCv7 PATCH 03/10] sched: scheduler-driven cpu frequency selection On Sat, Feb 27, 2016 at 01:08:02AM +0100, Rafael J. Wysocki wrote: > @@ -95,18 +98,20 @@ EXPORT_SYMBOL_GPL(cpufreq_set_update_uti > * > * This function is called by the scheduler on every invocation of > * update_load_avg() on the CPU whose utilization is being updated. > + * > + * It can only be called from RCU-sched read-side critical sections. > */ > void cpufreq_update_util(u64 time, unsigned long util, unsigned long max) > { > struct update_util_data *data; > > - rcu_read_lock(); > - Maybe, just because I'm paranoid, add something like: #ifdef CONFIG_LOCKDEP WARN_ON(debug_locks && !rcu_read_lock_sched_held()); #endif > data = rcu_dereference(*this_cpu_ptr(&cpufreq_update_util_data)); > - if (data && data->func) > + /* > + * If this isn't inside of an RCU-sched read-side critical section, data > + * may become NULL after the check below. > + */ > + if (data) > data->func(data, time, util, max); > - > - rcu_read_unlock(); > }
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