"Rafael J. Wysocki" <[email protected]> writes:
> On Thu, May 12, 2022 at 3:52 PM Schspa Shi <[email protected]> wrote:
>>
>> cpufreq_offline() calls offline() and exit() under the policy rwsem
>> But they are called outside the rwsem in cpufreq_online().
>>
>> This patch move the offline(), exit(), online(), init() to be inside
>> of policy rwsem to achieve a clear lock relationship.
>>
>> All the init() online() implement only initialize policy object without
>> holding this lock and won't call cpufreq APIs need to hold this lock.
>>
>> Signed-off-by: Schspa Shi <[email protected]>
>
> IMV this still addresses 2 different issues and so it should be split
> into 2 different patches.
>
>> ---
>> drivers/cpufreq/cpufreq.c | 5 ++---
>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
>> index 35dffd738580..f242d5488364 100644
>> --- a/drivers/cpufreq/cpufreq.c
>> +++ b/drivers/cpufreq/cpufreq.c
>
> Patch 1:
>
>> @@ -1343,12 +1343,12 @@ static int cpufreq_online(unsigned int cpu)
>> down_write(&policy->rwsem);
>> policy->cpu = cpu;
>> policy->governor = NULL;
>> - up_write(&policy->rwsem);
>> } else {
>> new_policy = true;
>> policy = cpufreq_policy_alloc(cpu);
>> if (!policy)
>> return -ENOMEM;
>> + down_write(&policy->rwsem);
>> }
>>
>> if (!new_policy && cpufreq_driver->online) {
>> @@ -1388,7 +1388,6 @@ static int cpufreq_online(unsigned int cpu)
>> cpumask_copy(policy->related_cpus, policy->cpus);
>> }
>>
>> - down_write(&policy->rwsem);
>> /*
>> * affected cpus must always be the one, which are online. We aren't
>> * managing offline cpus here.
>
> which addresses the problem that cpufreq_online() updates the
> policy->cpus and related_cpus masks without holding the policy rwsem
> (since the policy kobject has been registered already at this point,
> this is generally unsafe).
>
> A side-effect of it is that ->online() and ->init() will be called
> under the policy rwsem now, but that should be fine and is more
> consistent than the current code too.
>
> Patch 2:
>
>> @@ -1540,7 +1539,6 @@ static int cpufreq_online(unsigned int cpu)
>> remove_cpu_dev_symlink(policy, get_cpu_device(j));
>>
>> cpumask_clear(policy->cpus);
>> - up_write(&policy->rwsem);
>>
>> out_offline_policy:
>> if (cpufreq_driver->offline)
>> @@ -1549,6 +1547,7 @@ static int cpufreq_online(unsigned int cpu)
>> out_exit_policy:
>> if (cpufreq_driver->exit)
>> cpufreq_driver->exit(policy);
>> + up_write(&policy->rwsem);
>>
>> out_free_policy:
>> cpufreq_policy_free(policy);
>> --
>
> which addressed the issue of calling ->offline() and ->exit() without
> holding the policy rwsem that is at best inconsistent with
> cpufreq_offline().
No, we can't split this into two different patches. which will cause a
uninitialized unlock for policy rwsem.
This will make the git bitsec unusable.
Which Dan Carpenter reported, and cause the patch of the v1 version to
be reverted.
Link: https://lore.kernel.org/all/YnKZCGaig+EXSowf@kili/
---
BRs
Schspa Shi