On 06/02/2015 11:41 AM, Viresh Kumar wrote:
> On 02-06-15, 11:33, Preeti U Murthy wrote:
>> No, dbs_data is a governor wide data structure and not a policy wide
>
> Yeah, that's the common part which I was referring to. But normally
> its just read for policies in START/STOP, they just update per-cpu
> data for policy->cpus.
>
>> one, which is manipulated in START/STOP calls for drivers where the
>> CPUFREQ_HAVE_GOVERNOR_PER_POLICY is not set.
>>
>> So even if we assume that we hold per-policy locks, the following race
>> is still present. Assume that we have just two cpus which do not have a
>> governor-per-policy set.
>>
>> CPU0 CPU1
>>
>> store* store*
>>
>> lock(policy 1) lock(policy 2)
>> cpufreq_set_policy() cpufreq_set_policy()
>> EXIT() :
>> dbs-data->usage_count--
>>
>> INIT()
>> dbs_data exists
>
> You missed the usage_count++ here.
Ok, sorry about that. How about the below ?
>
>> so return
>> EXIT()
>> dbs_data->usage_count -- = 0
>> kfree(dbs_data)
>
> And so this shouldn't happen. Else we
> are missing locking in governor's
> code, rather than cpufreq.c
>
CPU0 CPU1
store* store*
lock(policy 1) lock(policy 2)
cpufreq_set_policy() cpufreq_set_policy()
EXIT() :
dbs-data->usage_count--
INIT() EXIT()
dbs_data exists dbs_data->usage_count -- = 0
kfree(dbs_data)
dbs-data->usage_count++
*NULL dereference*
The point is there are potential race conditions. Its just a matter of
interleaving ?
Regards
Preeti U Murthy
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
