On (07/11/13 10:43), Michael Wang wrote: > Hi, Sergey > > On 07/11/2013 07:13 AM, Sergey Senozhatsky wrote: > [snip] > > > > > > Please kindly review the following patch. > > > > > > > > Remove cpu device only upon succesful cpu down on CPU_POST_DEAD event, > > so we can kill off CPU_DOWN_FAILED case and eliminate potential extra > > remove/add path: > > > > hotplug lock > > CPU_DOWN_PREPARE: __cpufreq_remove_dev > > CPU_DOWN_FAILED: cpufreq_add_dev > > hotplug unlock > > > > Since cpu still present on CPU_DEAD event, cpu stats table should be > > kept longer and removed later on CPU_POST_DEAD as well. > > > > Because CPU_POST_DEAD action performed with hotplug lock released, CPU_DOWN > > might block existing gov_queue_work() user (blocked on get_online_cpus()) > > and unblock it with one of policy->cpus offlined, thus cpu_is_offline() > > check is performed in __gov_queue_work(). > > > > Besides, existing gov_queue_work() hotplug guard extended to protect all > > __gov_queue_work() calls: for both all_cpus and !all_cpus cases. > > > > CPUFREQ_GOV_START performs direct __gov_queue_work() call because hotplug > > lock already held there, opposing to previous gov_queue_work() and nested > > get/put_online_cpus(). > > Nice to know you have some idea on solving the issue ;-) > > I'm not sure whether I catch the idea, but seems like you are trying > to re-organize the timing of add/remove device. > > I'm sure that we have more than one way to solve the issues, but what > we need is the cure of root... > > As Srivatsa discovered, the root issue may be: > gov_cancel_work() failed to stop all the work after it's return. > > And Viresh also confirmed that this is not by-designed. > > Which means gov_queue_work() invoked by od_dbs_timer() is supposed to > never happen after CPUFREQ_GOV_STOP notify, the whole policy should > stop working at that time. > > But it failed to, and the work concurrent with cpu dying caused the > first problem. > > Thus I think we should focus on this and suggested below fix, I'd like > to know your opinions :) >
Hello Michael, nice job! works fine for me. Reported-and-Tested-by: Sergey Senozhatsky <[email protected]> -ss > Regards, > Michael Wang > > diff --git a/drivers/cpufreq/cpufreq_governor.c > b/drivers/cpufreq/cpufreq_governor.c > index dc9b72e..a64b544 100644 > --- a/drivers/cpufreq/cpufreq_governor.c > +++ b/drivers/cpufreq/cpufreq_governor.c > @@ -178,13 +178,14 @@ void gov_queue_work(struct dbs_data *dbs_data, struct > cpufreq_policy *policy, > { > int i; > > + if (dbs_data->queue_stop) > + return; > + > if (!all_cpus) { > __gov_queue_work(smp_processor_id(), dbs_data, delay); > } else { > - get_online_cpus(); > for_each_cpu(i, policy->cpus) > __gov_queue_work(i, dbs_data, delay); > - put_online_cpus(); > } > } > EXPORT_SYMBOL_GPL(gov_queue_work); > @@ -193,12 +194,27 @@ static inline void gov_cancel_work(struct dbs_data > *dbs_data, > struct cpufreq_policy *policy) > { > struct cpu_dbs_common_info *cdbs; > - int i; > + int i, round = 2; > > + dbs_data->queue_stop = 1; > +redo: > + round--; > for_each_cpu(i, policy->cpus) { > cdbs = dbs_data->cdata->get_cpu_cdbs(i); > cancel_delayed_work_sync(&cdbs->work); > } > + > + /* > + * Since there is no lock to prvent re-queue the > + * cancelled work, some early cancelled work might > + * have been queued again by later cancelled work. > + * > + * Flush the work again with dbs_data->queue_stop > + * enabled, this time there will be no survivors. > + */ > + if (round) > + goto redo; > + dbs_data->queue_stop = 0; > } > > /* Will return if we need to evaluate cpu load again or not */ > diff --git a/drivers/cpufreq/cpufreq_governor.h > b/drivers/cpufreq/cpufreq_governor.h > index e16a961..9116135 100644 > --- a/drivers/cpufreq/cpufreq_governor.h > +++ b/drivers/cpufreq/cpufreq_governor.h > @@ -213,6 +213,7 @@ struct dbs_data { > unsigned int min_sampling_rate; > int usage_count; > void *tuners; > + int queue_stop; > > /* dbs_mutex protects dbs_enable in governor start/stop */ > struct mutex mutex; > > > > > Signed-off-by: Sergey Senozhatsky <[email protected]> > > > > --- > > > > drivers/cpufreq/cpufreq.c | 5 +---- > > drivers/cpufreq/cpufreq_governor.c | 17 +++++++++++------ > > drivers/cpufreq/cpufreq_stats.c | 2 +- > > 3 files changed, 13 insertions(+), 11 deletions(-) > > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > > index 6a015ad..f8aacf1 100644 > > --- a/drivers/cpufreq/cpufreq.c > > +++ b/drivers/cpufreq/cpufreq.c > > @@ -1943,13 +1943,10 @@ static int __cpuinit cpufreq_cpu_callback(struct > > notifier_block *nfb, > > case CPU_ONLINE: > > cpufreq_add_dev(dev, NULL); > > break; > > - case CPU_DOWN_PREPARE: > > + case CPU_POST_DEAD: > > case CPU_UP_CANCELED_FROZEN: > > __cpufreq_remove_dev(dev, NULL); > > break; > > - case CPU_DOWN_FAILED: > > - cpufreq_add_dev(dev, NULL); > > - break; > > } > > } > > return NOTIFY_OK; > > diff --git a/drivers/cpufreq/cpufreq_governor.c > > b/drivers/cpufreq/cpufreq_governor.c > > index 4645876..681d5d6 100644 > > --- a/drivers/cpufreq/cpufreq_governor.c > > +++ b/drivers/cpufreq/cpufreq_governor.c > > @@ -125,7 +125,11 @@ static inline void __gov_queue_work(int cpu, struct > > dbs_data *dbs_data, > > unsigned int delay) > > { > > struct cpu_dbs_common_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu); > > - > > + /* cpu offline might block existing gov_queue_work() user, > > + * unblocking it after CPU_DEAD and before CPU_POST_DEAD. > > + * thus potentially we can hit offlined CPU */ > > + if (unlikely(cpu_is_offline(cpu))) > > + return; > > mod_delayed_work_on(cpu, system_wq, &cdbs->work, delay); > > } > > > > @@ -133,15 +137,14 @@ void gov_queue_work(struct dbs_data *dbs_data, struct > > cpufreq_policy *policy, > > unsigned int delay, bool all_cpus) > > { > > int i; > > - > > + get_online_cpus(); > > if (!all_cpus) { > > __gov_queue_work(smp_processor_id(), dbs_data, delay); > > } else { > > - get_online_cpus(); > > for_each_cpu(i, policy->cpus) > > __gov_queue_work(i, dbs_data, delay); > > - put_online_cpus(); > > } > > + put_online_cpus(); > > } > > EXPORT_SYMBOL_GPL(gov_queue_work); > > > > @@ -354,8 +357,10 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy, > > /* Initiate timer time stamp */ > > cpu_cdbs->time_stamp = ktime_get(); > > > > - gov_queue_work(dbs_data, policy, > > - delay_for_sampling_rate(sampling_rate), true); > > + /* hotplug lock already held */ > > + for_each_cpu(j, policy->cpus) > > + __gov_queue_work(j, dbs_data, > > + delay_for_sampling_rate(sampling_rate)); > > break; > > > > case CPUFREQ_GOV_STOP: > > diff --git a/drivers/cpufreq/cpufreq_stats.c > > b/drivers/cpufreq/cpufreq_stats.c > > index cd9e817..833816e 100644 > > --- a/drivers/cpufreq/cpufreq_stats.c > > +++ b/drivers/cpufreq/cpufreq_stats.c > > @@ -355,7 +355,7 @@ static int __cpuinit cpufreq_stat_cpu_callback(struct > > notifier_block *nfb, > > case CPU_DOWN_PREPARE: > > cpufreq_stats_free_sysfs(cpu); > > break; > > - case CPU_DEAD: > > + case CPU_POST_DEAD: > > cpufreq_stats_free_table(cpu); > > break; > > case CPU_UP_CANCELED_FROZEN: > > -- > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > the body of a message to [email protected] > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > Please read the FAQ at http://www.tux.org/lkml/ > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
