• Viresh Kumar's avatar
    cpufreq: stats: handle cpufreq_unregister_driver() and suspend/resume properly · fcd7af91
    Viresh Kumar authored
    There are several problems with cpufreq stats in the way it handles
    cpufreq_unregister_driver() and suspend/resume..
    
     - We must not lose data collected so far when suspend/resume happens
       and so stats directories must not be removed/allocated during these
       operations, which is done currently.
    
     - cpufreq_stat has registered notifiers with both cpufreq and hotplug.
       It adds sysfs stats directory with a cpufreq notifier: CPUFREQ_NOTIFY
       and removes this directory with a notifier from hotplug core.
    
       In case cpufreq_unregister_driver() is called (on rmmod cpufreq driver),
       stats directories per cpu aren't removed as CPUs are still online. The
       only call cpufreq_stats gets is cpufreq_stats_update_policy_cpu() for
       all CPUs except the last of each policy. And pointer to stat information
       is stored in the entry for last CPU in the per-cpu cpufreq_stats_table.
       But policy structure would be freed inside cpufreq core and so that will
       result in memory leak inside cpufreq stats (as we are never freeing
       memory for stats).
    
       Now if we again insert the module cpufreq_register_driver() will be
       called and we will again allocate stats data and put it on for first
       CPU of every policy.  In case we only have a single CPU per policy, we
       will return with a error from cpufreq_stats_create_table() due to this
       code:
    
    	if (per_cpu(cpufreq_stats_table, cpu))
    		return -EBUSY;
    
       And so probably cpufreq stats directory would not show up anymore (as
       it was added inside last policies->kobj which doesn't exist anymore).
       I haven't tested it, though. Also the values in stats files wouldn't
       be refreshed as we are using the earlier stats structure.
    
     - CPUFREQ_NOTIFY is called from cpufreq_set_policy() which is called for
       scenarios where we don't really want cpufreq_stat_notifier_policy() to get
       called. For example whenever we are changing anything related to a policy:
       min/max/current freq, etc. cpufreq_set_policy() is called and so cpufreq
       stats is notified. Where we don't do any useful stuff other than simply
       returning with -EBUSY from cpufreq_stats_create_table(). And so this
       isn't the right notifier that cpufreq stats..
    
     Due to all above reasons this patch does following changes:
     - Add new notifiers CPUFREQ_CREATE_POLICY and CPUFREQ_REMOVE_POLICY,
       which are only called when policy is created/destroyed. They aren't
       called for suspend/resume paths..
     - Use these notifiers in cpufreq_stat_notifier_policy() to create/destory
       stats sysfs entries. And so cpufreq_unregister_driver() or suspend/resume
       shouldn't be a problem for cpufreq_stats.
     - Return early from cpufreq_stat_cpu_callback() for suspend/resume sequence,
       so that we don't free stats structure.
    Acked-by: default avatarNicolas Pitre <nico@linaro.org>
    Tested-by: default avatarNicolas Pitre <nico@linaro.org>
    Signed-off-by: default avatarViresh Kumar <viresh.kumar@linaro.org>
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    fcd7af91
cpufreq_stats.c 10.5 KB