Re: [v3.10 regression] deadlock on cpu hotplug

[Michael Wang]

Hi, Bartlomiej

On 07/08/2013 11:26 PM, Bartlomiej Zolnierkiewicz wrote:
[snip]
> 
> # echo 0 > /sys/devices/system/cpu/cpu3/online
> # echo 0 > /sys/devices/system/cpu/cpu2/online
> # echo 0 > /sys/devices/system/cpu/cpu1/online
> # while true;do echo 1 > /sys/devices/system/cpu/cpu1/online;echo 0 > /sys/devices/system/cpu/cpu1/online;done
> 
> The commit in question (2f7021a8) was merged in v3.10-rc5 as a fix for
> commit 031299b ("cpufreq: governors: Avoid unnecessary per cpu timer
> interrupts") which was causing a kernel warning to show up.
> 
> Michael/Viresh: do you have some idea how to fix the issue?

Thanks for the report :) would you like to take a try
on below patch and see whether it solve the issue?

diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 5af40ad..aa05eaa 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -229,6 +229,8 @@ static void set_sampling_rate(struct dbs_data *dbs_data,
        }
 }
 
+static struct lock_class_key j_cdbs_key;
+
 int cpufreq_governor_dbs(struct cpufreq_policy *policy,
                struct common_dbs_data *cdata, unsigned int event)
 {
@@ -366,6 +368,8 @@ int (struct cpufreq_policy *policy,
                                        kcpustat_cpu(j).cpustat[CPUTIME_NICE];
 
                        mutex_init(&j_cdbs->timer_mutex);
+                       lockdep_set_class(&j_cdbs->timer_mutex, &j_cdbs_key);
+
                        INIT_DEFERRABLE_WORK(&j_cdbs->work,
                                             dbs_data->cdata->gov_dbs_timer);
                }

Regards,
Michael Wang

> 
> Best regards,
> --
> Bartlomiej Zolnierkiewicz
> Samsung R&D Institute Poland
> Samsung Electronics
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