Messages in this thread | | | Date | Mon, 14 Jul 2014 12:08:24 -0700 | From | Saravana Kannan <> | Subject | Re: [PATCH v2] cpufreq: Don't destroy/realloc policy/sysfs on hotplug/suspend |
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On 07/13/2014 11:09 PM, Viresh Kumar wrote: > On 12 July 2014 08:14, Saravana Kannan <skannan@codeaurora.org> wrote: > >>>> I'm just always adding the real nodes to the first CPU in a cluster >>>> independent of which CPU gets added first. Makes it easier to know which >>>> ones to symlink. See comment next to policy->cpu for full context. >>> >>> >>> Yeah, and that is the order in which CPUs will boot and cpufreq_add_dev() >>> will be called. So, isn't policy->cpu the right CPU always? >> >> >> No, the "first" cpu in a cluster doesn't need to be the first one to be >> added. An example is 2x2 cluster system where the system is booted with max >> cpus = 2 and then cpu3 could be onlined first by userspace. > > Because we are getting rid of much of the complexity now, I do not want > policy->cpu to keep changing. Just fix it up to the cpu for which the policy > gets created first. That's it. No more changes required. It doesn't matter at > userspace which cpu owns it as symlinks would anyway duplicate it under > every cpu.
I think you missed one my of comments in the email. I agree with what you are saying here. I'll just do it as a separate patch to keep this one simpler. I don't want to touch all the governors and other potential uses of policy->cpu in this patch.
>> Yeah, it is pretty convolution. But pretty much anywhere in the gov code >> where policy->cpu is used could cause this. The specific crash I hit was in >> this code: >> >> static void od_dbs_timer(struct work_struct *work) >> { >> struct od_cpu_dbs_info_s *dbs_info = >> container_of(work, struct od_cpu_dbs_info_s, >> cdbs.work.work); >> unsigned int cpu = dbs_info->cdbs.cur_policy->cpu; >> >> ======= CPU is policy->cpu here. >> >> struct od_cpu_dbs_info_s *core_dbs_info = &per_cpu(od_cpu_dbs_info, >> cpu); >> >> ======= Picks the per CPU struct of an offline CPU >> >> <snip> >> >> mutex_lock(&core_dbs_info->cdbs.timer_mutex); >> >> ======= Dies trying to lock a destroyed mutex > > I am still not getting it. Why would we get into this if policy->cpu is fixed > once at boot ? >
Yeah, it definitely crashes if policy->cpu if an offline cpu. Because the mutex would be uninitialized if it's stopped after boot or it would never have been initialized (depending on how you fix policy->cpu at boot).
Look at this snippet on the actual tree and it should be pretty evident.
-Saravana
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