Re: [PATCH] drm/i915/gt: debugfs: Evaluate forcewake usage within locks

[Nirmoy Das <nirmoy.das@linux.intel.com>]

On 6/11/2024 3:58 PM, Tvrtko Ursulin wrote:
>
> On 10/06/2024 10:24, Nirmoy Das wrote:
>> Hi Andi,
>>
>> On 6/7/2024 4:51 PM, Andi Shyti wrote:
>>> The forcewake count and domains listing is multi process critical
>>> and the uncore provides a spinlock for such cases.
>>>
>>> Lock the forcewake evaluation section in the fw_domains_show()
>>> debugfs interface.
>>>
>>> Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
>>
>> Needs a Fixes tag, below seems to be correct one.
>>
>>
>> Fixes: 9dd4b065446a ("drm/i915/gt: Move pm debug files into a gt 
>> aware debugfs")
>>
>> Cc: <stable@vger.kernel.org> # v5.6+
>>
>> Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
>
> What is the back story here and why would it need backporting? IGT 
> cares about the atomic view of user_forcewake_count and individual 
> domains or what?

There is no serious back story. This came from a static code analyzer 
report. I keep forgetting debugfs isn't mounted on production systems so 
we don't have to backport this patch.


Thanks,

Nirmoy

>
> Regards,
>
> Tvrtko
>
>
>>
>> Regards,
>>
>> Nirmoy
>>
>>
>>> ---
>>>   drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c 
>>> b/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c
>>> index 4fcba42cfe34..0437fd8217e0 100644
>>> --- a/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c
>>> +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm_debugfs.c
>>> @@ -71,6 +71,8 @@ static int fw_domains_show(struct seq_file *m, 
>>> void *data)
>>>       struct intel_uncore_forcewake_domain *fw_domain;
>>>       unsigned int tmp;
>>> +    spin_lock_irq(&uncore->lock);
>>> +
>>>       seq_printf(m, "user.bypass_count = %u\n",
>>>              uncore->user_forcewake_count);
>>> @@ -79,6 +81,8 @@ static int fw_domains_show(struct seq_file *m, 
>>> void *data)
>>> intel_uncore_forcewake_domain_to_str(fw_domain->id),
>>>                  READ_ONCE(fw_domain->wake_count));
>>> +    spin_unlock_irq(&uncore->lock);
>>> +
>>>       return 0;
>>>   }
>>>   DEFINE_INTEL_GT_DEBUGFS_ATTRIBUTE(fw_domains);