diff mbox series

[v2] drm/i915/pmu: avoid -Wmaybe-uninitialized warning

Message ID 20180313161952.552083-1-arnd@arndb.de
State New
Headers show
Series [v2] drm/i915/pmu: avoid -Wmaybe-uninitialized warning | expand

Commit Message

Arnd Bergmann March 13, 2018, 4:19 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>

---
v2: removed unused function argument, fixed 'break' statement.
---
 drivers/gpu/drm/i915/i915_pmu.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

-- 
2.9.0

Comments

Chris Wilson March 13, 2018, 4:38 p.m. UTC | #1 
Quoting Arnd Bergmann (2018-03-13 16:19:31)
> 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>

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

-Chris
Tvrtko Ursulin March 13, 2018, 5:46 p.m. UTC | #2 
On 13/03/2018 16:19, Arnd Bergmann wrote:
> 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]


Hm, how does paravirt_types.h comes into the picture?

> 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.


Is it specific gcc version, specific options, or specific kernel config 
that this happens?

Strange that it hasn't been seen so far.

Regards,

Tvrtko

> Fixes: 1fe699e30113 ("drm/i915/pmu: Fix sleep under atomic in RC6 readout")

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

> ---

> v2: removed unused function argument, fixed 'break' statement.

> ---

>   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..d6b9b6b5fb98 100644

> --- a/drivers/gpu/drm/i915/i915_pmu.c

> +++ b/drivers/gpu/drm/i915/i915_pmu.c

> @@ -412,10 +412,9 @@ static u64 __get_rc6(struct drm_i915_private *i915)

>   	return val;

>   }

>   

> -static u64 get_rc6(struct drm_i915_private *i915, bool locked)

> +static u64 get_rc6(struct drm_i915_private *i915)

>   {

>   #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;

> @@ -519,7 +506,15 @@ 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);

> +			if (!locked) {

> +				unsigned long flags;

> +

> +				spin_lock_irqsave(&i915->pmu.lock, flags);

> +				val = get_rc6(i915);

> +				spin_unlock_irqrestore(&i915->pmu.lock, flags);

> +			} else {

> +				val = get_rc6(i915);

> +			}

>   			break;

>   		}

>   	}

>
diff mbox series

Patch

diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c
index 4bc7aefa9541..d6b9b6b5fb98 100644
--- a/drivers/gpu/drm/i915/i915_pmu.c
+++ b/drivers/gpu/drm/i915/i915_pmu.c
@@ -412,10 +412,9 @@  static u64 __get_rc6(struct drm_i915_private *i915)
 	return val;
 }
 
-static u64 get_rc6(struct drm_i915_private *i915, bool locked)
+static u64 get_rc6(struct drm_i915_private *i915)
 {
 #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;
@@ -519,7 +506,15 @@  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);
+			if (!locked) {
+				unsigned long flags;
+
+				spin_lock_irqsave(&i915->pmu.lock, flags);
+				val = get_rc6(i915);
+				spin_unlock_irqrestore(&i915->pmu.lock, flags);
+			} else {
+				val = get_rc6(i915);
+			}
 			break;
 		}
 	}