drm/i915/pmu: avoid -Wmaybe-uninitialized warning
diff mbox

Message ID 20180313120848.2658626-1-arnd@arndb.de
State New
Headers show

Commit Message

Arnd Bergmann March 13, 2018, 12:08 p.m. UTC
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@arndb.de>
---
 drivers/gpu/drm/i915/i915_pmu.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

Comments

Chris Wilson March 13, 2018, 12:31 p.m. UTC | #1
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@arndb.de>
> ---
>  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?

>  {
>  #if IS_ENABLED(CONFIG_PM)
> -       unsigned long flags;
>         u64 val;
>  
>         if (intel_runtime_pm_get_if_in_use(i915)) {
> @@ -428,18 +427,12 @@ static u64 get_rc6(struct drm_i915_private *i915, bool locked)
>                  * previously.
>                  */
>  
> -               if (!locked)
> -                       spin_lock_irqsave(&i915->pmu.lock, flags);
> -
>                 if (val >= i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur) {
>                         i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur = 0;
>                         i915->pmu.sample[__I915_SAMPLE_RC6].cur = val;
>                 } else {
>                         val = i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur;
>                 }
> -
> -               if (!locked)
> -                       spin_unlock_irqrestore(&i915->pmu.lock, flags);
>         } else {
>                 struct pci_dev *pdev = i915->drm.pdev;
>                 struct device *kdev = &pdev->dev;
> @@ -452,9 +445,6 @@ static u64 get_rc6(struct drm_i915_private *i915, bool locked)
>                  * on top of the last known real value, as the approximated RC6
>                  * counter value.
>                  */
> -               if (!locked)
> -                       spin_lock_irqsave(&i915->pmu.lock, flags);
> -
>                 spin_lock_irqsave(&kdev->power.lock, flags2);
>  
>                 if (!i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur)
> @@ -470,9 +460,6 @@ static u64 get_rc6(struct drm_i915_private *i915, bool locked)
>                 val = jiffies_to_nsecs(val);
>                 val += i915->pmu.sample[__I915_SAMPLE_RC6].cur;
>                 i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur = val;
> -
> -               if (!locked)
> -                       spin_unlock_irqrestore(&i915->pmu.lock, flags);
>         }
>  
>         return val;
> @@ -519,8 +506,16 @@ static u64 __i915_pmu_event_read(struct perf_event *event, bool locked)
>                         val = count_interrupts(i915);
>                         break;
>                 case I915_PMU_RC6_RESIDENCY:
> -                       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.
-Chris
Arnd Bergmann March 13, 2018, 12:49 p.m. UTC | #2
On Tue, Mar 13, 2018 at 1:29 PM, Patchwork
<patchwork@emeril.freedesktop.org> wrote:
> == Series Details ==
>
> Series: drm/i915/pmu: avoid -Wmaybe-uninitialized warning
> URL   : https://patchwork.freedesktop.org/series/39857/
> State : warning
>
> == Summary ==
>
> $ dim sparse origin/drm-tip
> Commit: drm/i915/pmu: avoid -Wmaybe-uninitialized warning
> -O:drivers/gpu/drm/i915/i915_pmu.c:442:47: warning: context imbalance in 'get_rc6' - unexpected unlock
> +

This means I fixed a warning, not introduced one, right?

     Arnd
Arnd Bergmann March 13, 2018, 12:55 p.m. UTC | #3
On Tue, Mar 13, 2018 at 1:31 PM, Chris Wilson <chris@chris-wilson.co.uk> 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@arndb.de>
>> ---
>>  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

Patch
diff mbox

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)
 {
 #if IS_ENABLED(CONFIG_PM)
-	unsigned long flags;
 	u64 val;
 
 	if (intel_runtime_pm_get_if_in_use(i915)) {
@@ -428,18 +427,12 @@  static u64 get_rc6(struct drm_i915_private *i915, bool locked)
 		 * previously.
 		 */
 
-		if (!locked)
-			spin_lock_irqsave(&i915->pmu.lock, flags);
-
 		if (val >= i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur) {
 			i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur = 0;
 			i915->pmu.sample[__I915_SAMPLE_RC6].cur = val;
 		} else {
 			val = i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur;
 		}
-
-		if (!locked)
-			spin_unlock_irqrestore(&i915->pmu.lock, flags);
 	} else {
 		struct pci_dev *pdev = i915->drm.pdev;
 		struct device *kdev = &pdev->dev;
@@ -452,9 +445,6 @@  static u64 get_rc6(struct drm_i915_private *i915, bool locked)
 		 * on top of the last known real value, as the approximated RC6
 		 * counter value.
 		 */
-		if (!locked)
-			spin_lock_irqsave(&i915->pmu.lock, flags);
-
 		spin_lock_irqsave(&kdev->power.lock, flags2);
 
 		if (!i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur)
@@ -470,9 +460,6 @@  static u64 get_rc6(struct drm_i915_private *i915, bool locked)
 		val = jiffies_to_nsecs(val);
 		val += i915->pmu.sample[__I915_SAMPLE_RC6].cur;
 		i915->pmu.sample[__I915_SAMPLE_RC6_ESTIMATED].cur = val;
-
-		if (!locked)
-			spin_unlock_irqrestore(&i915->pmu.lock, flags);
 	}
 
 	return val;
@@ -519,8 +506,16 @@  static u64 __i915_pmu_event_read(struct perf_event *event, bool locked)
 			val = count_interrupts(i915);
 			break;
 		case I915_PMU_RC6_RESIDENCY:
-			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);
+			}
 		}
 	}