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Date: Sat, 23 Feb 2013 09:09:31 +0530 From: Viresh Kumar <viresh.kumar@...aro.org> To: Nathan Zimmer <nzimmer@....com> Cc: rjw@...k.pl, cpufreq@...r.kernel.org, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v4 2/2] cpufreq: Convert the cpufreq_driver_lock to use the rcu Hi Nathan, Sorry for pointing out this so late but i still feel we are missing something really important. On 22 February 2013 21:54, Nathan Zimmer <nzimmer@....com> wrote: > - read_lock_irqsave(&cpufreq_driver_lock, flags); > + rcu_read_lock(); > + freqs->flags = rcu_dereference(cpufreq_driver)->flags; > policy = per_cpu(cpufreq_cpu_data, freqs->cpu); > - read_unlock_irqrestore(&cpufreq_driver_lock, flags); > + rcu_read_unlock(); > - write_lock_irqsave(&cpufreq_driver_lock, flags); > + spin_lock_irqsave(&cpufreq_driver_lock, flags); > for_each_cpu(j, policy->cpus) { > per_cpu(cpufreq_cpu_data, j) = policy; > per_cpu(cpufreq_policy_cpu, j) = policy->cpu; > } > - write_unlock_irqrestore(&cpufreq_driver_lock, flags); > + spin_unlock_irqrestore(&cpufreq_driver_lock, flags); Look at how we are protecting cpufreq_cpu_data here. rcu_read_[un]lock() only marks the start/end of critical section. How are we sure here that cpufreq_cpu_data is not read simultaneously when we are updating it? rcu lock/unlock only works for cpufreq_driver pointer only and not for this data. We still need the same locking for for cpufreq_cpu_data. What do you say? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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