Messages in this thread | | | Date | Mon, 02 Feb 2015 23:04:41 +0800 | From | ethan zhao <> | Subject | Re: [PATCH Resend] cpufreq: Set cpufreq_cpu_data to NULL before putting kobject |
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On 2015/2/2 12:54, Viresh Kumar wrote: > On 2 February 2015 at 10:15, ethan zhao <ethan.zhao@oracle.com> wrote: >> On 2015/2/2 12:26, Viresh Kumar wrote: >> But there is no checking against refcount in or before >> >> cpufreq_policy_free(), that is one issue I mentioned. > As I said earlier, the completion will only fire once the refcount > is zero. And so there is no need of any check here. > >>> That routines doesn't have any tricks and simply frees the policy. >>> Because, before calling cpufreq_policy_put_kobj(), we have set >>> the per-cpu variable to NULL, nobody else will get the policy >> It is possible cpufreq_cpu_get() within the PPC thread was called just >> before __cpufreq_remove_dev_finish() is to be called in another thread, >> so you set the per_cpu(cpufreq_cpu_data, cpu) to NULL will not prevent >> the actions between cpufreq_cpu_get and cpufreq_cpu_put(). >> >> And then the freeing happens in __cpufreq_remove_dev_finish(). > It will.. You aren't looking closely enough. If cpufreq_cpu_get() is called just > before remove-dev, then cpufreq_cpu_get() will take: > > read_lock_irqsave(&cpufreq_driver_lock, flags); > > And it will do: > > read_unlock_irqrestore(&cpufreq_driver_lock, flags); > > only after increasing the refcount with kobject_get(). > > While on the other side __cpufreq_remove_dev_finish() will do this: > > write_lock_irqsave(&cpufreq_driver_lock, flags); > policy = per_cpu(cpufreq_cpu_data, cpu); > per_cpu(cpufreq_cpu_data, cpu) = NULL; > write_unlock_irqrestore(&cpufreq_driver_lock, flags); > > So, it will wait for the read_lock in cpufreq_cpu_get() to finish before > setting per-cpu variable to NULL. And so, after kobject_put() in > cpufreq_policy_put_kobj(), we will wait for the completion to fire Closely enough this time, understood, thanks for your explanation.
Ethan > and that will only happen once a corresponding cpufreq_cpu_put() > is issued.
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