Re: [PATCH] drm/i915/pmu: avoid -Wmaybe-uninitialized warning

[Arnd Bergmann]

On Tue, Mar 13, 2018 at 1:31 PM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> Quoting Arnd Bergmann (2018-03-13 12:08:29)
>> The conditional spinlock confuses gcc into thinking the 'flags' value
>> might contain uninitialized data:
>>
>> drivers/gpu/drm/i915/i915_pmu.c: In function '__i915_pmu_event_read':
>> arch/x86/include/asm/paravirt_types.h:573:3: error: 'flags' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>>
>> The code is correct, but it's easy to see how the compiler gets confused
>> here. This avoids the problem by pulling the lock outside of the function
>> into its only caller.
>>
>> Fixes: 1fe699e30113 ("drm/i915/pmu: Fix sleep under atomic in RC6 readout")
>> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
>> ---
>>  drivers/gpu/drm/i915/i915_pmu.c | 25 ++++++++++---------------
>>  1 file changed, 10 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
>> index 4bc7aefa9541..2c8c705d1f18 100644
>> --- a/drivers/gpu/drm/i915/i915_pmu.c
>> +++ b/drivers/gpu/drm/i915/i915_pmu.c
>> @@ -415,7 +415,6 @@ static u64 __get_rc6(struct drm_i915_private *i915)
>>  static u64 get_rc6(struct drm_i915_private *i915, bool locked)
>
> bool locked is now unused, right?

Right, removing it now.

>> -                       val = get_rc6(i915, locked);
>> -                       break;
>> +                       if (!locked) {
>> +                               unsigned long flags;
>> +
>> +                               spin_lock_irqsave(&i915->pmu.lock, flags);
>> +                               val = get_rc6(i915, locked);
>> +                               spin_unlock_irqrestore(&i915->pmu.lock, flags);
>> +                               break;
>> +                       } else {
>> +                               val = get_rc6(i915, locked);
>> +                       }
>
> break is now on one path only; should be here.

Fixed as well. I'll wait a bit for more comments before resending.

Thanks for the review!

     Arnd