Re: [PATCH 2/2] cpufreq: prevent lockup on reading scaling_available_frequencies

[Viresh Kumar <viresh.kumar@linaro.org>]

On 07-10-15, 09:18, Srinivas Pandruvada wrote:
> freq_table is allocated in init() callbacks and freed on exit()
> callback. But I don't see any driver changing policy->freq_table to NULL
> or setting value to policy->freq_table to their allocated freq_table .
 
That's what I am asking for.

> I see policy->freq_table is only assigned value in function
> cpufreq_table_validate_and_show, as part of the core API.

Its just an helper written to reduce code redundancy..

> So I think we
> should set to NULL after clients freed the freq_table as part of core
> function.

Not really. If we want to do the opposite, then we should initiate
policy->freq_table = NULL, right from exit(), as its done as part of
init() first.

> Otherwise we need to modify every client cpufreq driver and assign
> policy->freq_table=NULL on .exit().  Since they don't assign value to
> this policy->freq_table in first place, they shouldn't change this.

They did set it in the first place, with help of a helper routine
though.

But I do understand the code redundancy we are about to create. So,
maybe we can do this in the core as a special case.

But then you missed another location where exit() was called.

> Also I don't know why we need to keep the sysfs entry cpufreq after
> offline. There are other values, which we can read without crash, but
> may not be valid. We may delete this sysfs entry. But may be some
> cpufreq driver cares about this even after offline. If we can delete
> this entry, it can be part of cleanup of cpufreq subsystem.

Go thought the mail threads where that support is added, it was indeed
useful.

-- 
viresh