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

[Arnd Bergmann]

On Tue, Mar 13, 2018 at 1:31 PM, Chris Wilson  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 
>> ---
>>  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(>pmu.lock, flags);
>> +   val = get_rc6(i915, locked);
>> +   spin_unlock_irqrestore(>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

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

[Arnd Bergmann]

On Tue, Mar 13, 2018 at 1:31 PM, Chris Wilson  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 
>> ---
>>  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(>pmu.lock, flags);
>> +   val = get_rc6(i915, locked);
>> +   spin_unlock_irqrestore(>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

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

[Chris Wilson]

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 
> ---
>  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(>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(>pmu.lock, flags);
> } else {
> struct pci_dev *pdev = i915->drm.pdev;
> struct device *kdev = >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(>pmu.lock, flags);
> -
> spin_lock_irqsave(>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(>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(>pmu.lock, flags);
> +   val = get_rc6(i915, locked);
> +   spin_unlock_irqrestore(>pmu.lock, 
> flags);
> +   break;
> +   } else {
> +   val = get_rc6(i915, locked);
> +   }

break is now on one path only; should be here.
-Chris

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

[Chris Wilson]

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 
> ---
>  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(>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(>pmu.lock, flags);
> } else {
> struct pci_dev *pdev = i915->drm.pdev;
> struct device *kdev = >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(>pmu.lock, flags);
> -
> spin_lock_irqsave(>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(>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(>pmu.lock, flags);
> +   val = get_rc6(i915, locked);
> +   spin_unlock_irqrestore(>pmu.lock, 
> flags);
> +   break;
> +   } else {
> +   val = get_rc6(i915, locked);
> +   }

break is now on one path only; should be here.
-Chris

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

[Arnd Bergmann]

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 
---
 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)
 {
 #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(>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(>pmu.lock, flags);
} else {
struct pci_dev *pdev = i915->drm.pdev;
struct device *kdev = >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(>pmu.lock, flags);
-
spin_lock_irqsave(>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(>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(>pmu.lock, flags);
+   val = get_rc6(i915, locked);
+   spin_unlock_irqrestore(>pmu.lock, flags);
+   break;
+   } else {
+   val = get_rc6(i915, locked);
+   }
}
}
 
-- 
2.9.0

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

[Arnd Bergmann]

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 
---
 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)
 {
 #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(>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(>pmu.lock, flags);
} else {
struct pci_dev *pdev = i915->drm.pdev;
struct device *kdev = >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(>pmu.lock, flags);
-
spin_lock_irqsave(>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(>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(>pmu.lock, flags);
+   val = get_rc6(i915, locked);
+   spin_unlock_irqrestore(>pmu.lock, flags);
+   break;
+   } else {
+   val = get_rc6(i915, locked);
+   }
}
}
 
-- 
2.9.0