On 07/10/2014 10:49 AM, Viresh Kumar wrote:
> This is only relevant to implementations with multiple clusters, where clusters
> have separate clock lines but all CPUs within a cluster share it.
>
> Consider a dual cluster platform with 2 cores per cluster. During suspend we
> start offlining CPUs from 1 to 3. When CPU2 is remove, policy->kobj would be
> moved to CPU3 and when CPU3 goes down we wouldn't free policy or its kobj.
>
> Now on resume, we will get CPU2 before CPU3 and will call __cpufreq_add_dev().
> We will recover the old policy and update policy->cpu from 3 to 2 from
> update_policy_cpu().
>
> But the kobj is still tied to CPU3 and wasn't moved to CPU2. We wouldn't create
> a link for CPU2, but would try that while bringing CPU3 online. Which will
> report errors as CPU3 already has kobj assigned to it.
>
> This bug got introduced with commit 42f921a, which overlooked this scenario.
>
> To fix this, lets move kobj to the new policy->cpu while bringing first CPU of a
> cluster back.
>
> Fixes: ("42f921a cpufreq: remove sysfs files for CPUs which failed to come back after resume")
> Cc: Stable <stable@xxxxxxxxxxxxxxx> # 3.13+
> Reported-by: Bu Yitian <ybu@xxxxxxxxxxxxxxxx>
> Reported-by: Saravana Kannan <skannan@xxxxxxxxxxxxxx>
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
Looks good to me. But I think it would be better to move the invocation of
kobject_move() to update_policy_cpu() itself, so that update_policy_cpu()
will do all the work involved in updating the policy->cpu, as its name suggests.
With that small nit,
Reviewed-by: Srivatsa S. Bhat <srivatsa@xxxxxxx>
Regards,
Srivatsa S. Bhat
> Hi Rafael,
>
> This is for 3.16 release, please take it once Yitian/Saravana test this out.
>
> @Yitian/Saravana: Sorry of overlooking this when both of you reported this
> first. I (and Srivatsa as well) was damn sure that this scenario is taken into
> account in current code and a close look proved that wrong.
>
> I couldn't test it out, can any of you please see if it fixes things for you?
>
> drivers/cpufreq/cpufreq.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 62259d2..6f02485 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1153,10 +1153,12 @@ static int __cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
> * the creation of a brand new one. So we need to perform this update
> * by invoking update_policy_cpu().
> */
> - if (recover_policy && cpu != policy->cpu)
> + if (recover_policy && cpu != policy->cpu) {
> update_policy_cpu(policy, cpu);
> - else
> + WARN_ON(kobject_move(&policy->kobj, &dev->kobj));
> + } else {
> policy->cpu = cpu;
> + }
>
> cpumask_copy(policy->cpus, cpumask_of(cpu));
>
>
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