[08/12] drm/i915: Fix struct mutex vs. RPS lock inversion
diff mbox

Message ID 1454411190-15721-9-git-send-email-tvrtko.ursulin@linux.intel.com
State New
Headers show

Commit Message

Tvrtko Ursulin Feb. 2, 2016, 11:06 a.m. UTC
From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

RPS lock must be taken before the struct_mutex to avoid
locking inversion. So stop grabbing it for the whole
powersave initialization and instead only take it during
the sections which need it.

Also, struct_mutex is not needed any more since dedicated
RPS lock was added in:

   commit 4fc688ce79772496503d22263d61b071a8fb596e
   Author: Jesse Barnes <jbarnes@virtuousgeek.org>
   Date:   Fri Nov 2 11:14:01 2012 -0700

       drm/i915: protect RPS/RC6 related accesses (including PCU) with a new mutex

Based on prototype patch by Chris Wilson and a subsequent
mailing list discussion involving Ville, Imre, Chris and
Daniel.

v2: More details in the commit.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_display.c | 4 ----
 drivers/gpu/drm/i915/intel_pm.c      | 9 +++++----
 2 files changed, 5 insertions(+), 8 deletions(-)

Comments

Chris Wilson Feb. 2, 2016, 1:16 p.m. UTC | #1
On Tue, Feb 02, 2016 at 11:06:26AM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> RPS lock must be taken before the struct_mutex to avoid
> locking inversion. So stop grabbing it for the whole
> powersave initialization and instead only take it during
> the sections which need it.
> 
> Also, struct_mutex is not needed any more since dedicated
> RPS lock was added in:
> 
>    commit 4fc688ce79772496503d22263d61b071a8fb596e
>    Author: Jesse Barnes <jbarnes@virtuousgeek.org>
>    Date:   Fri Nov 2 11:14:01 2012 -0700
> 
>        drm/i915: protect RPS/RC6 related accesses (including PCU) with a new mutex
> 
> Based on prototype patch by Chris Wilson and a subsequent
> mailing list discussion involving Ville, Imre, Chris and
> Daniel.
> 
> v2: More details in the commit.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Imre Deak <imre.deak@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 4 ----
>  drivers/gpu/drm/i915/intel_pm.c      | 9 +++++----
>  2 files changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 5018295cd92b..af0d33a3697a 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -15995,9 +15995,7 @@ void intel_modeset_gem_init(struct drm_device *dev)
>  	struct drm_i915_gem_object *obj;
>  	int ret;
>  
> -	mutex_lock(&dev->struct_mutex);
>  	intel_init_gt_powersave(dev);
> -	mutex_unlock(&dev->struct_mutex);
>  
>  	intel_modeset_init_hw(dev);
>  
> @@ -16077,9 +16075,7 @@ void intel_modeset_cleanup(struct drm_device *dev)
>  
>  	intel_cleanup_overlay(dev);
>  
> -	mutex_lock(&dev->struct_mutex);
>  	intel_cleanup_gt_powersave(dev);
> -	mutex_unlock(&dev->struct_mutex);

The whitespace no longer conveys meaning, it used to be to clearly mark
the mutex section.

> @@ -5235,6 +5233,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
>  out:
>  	DRM_DEBUG_DRIVER("PCBR: 0x%08x\n", I915_READ(VLV_PCBR));
>  	dev_priv->vlv_pctx = pctx;
> +	mutex_unlock(&dev->struct_mutex);
>  }
>  
>  static void valleyview_cleanup_pctx(struct drm_device *dev)
> @@ -5244,8 +5243,10 @@ static void valleyview_cleanup_pctx(struct drm_device *dev)
>  	if (WARN_ON(!dev_priv->vlv_pctx))
>  		return;
>  
> +	mutex_lock(&dev->struct_mutex);
>  	drm_gem_object_unreference(&dev_priv->vlv_pctx->base);
>  	dev_priv->vlv_pctx = NULL;
> +	mutex_unlock(&dev->struct_mutex);

This made me smile.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
-Chris
Tvrtko Ursulin Feb. 2, 2016, 2:13 p.m. UTC | #2
On 02/02/16 13:16, Chris Wilson wrote:
> On Tue, Feb 02, 2016 at 11:06:26AM +0000, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> RPS lock must be taken before the struct_mutex to avoid
>> locking inversion. So stop grabbing it for the whole
>> powersave initialization and instead only take it during
>> the sections which need it.
>>
>> Also, struct_mutex is not needed any more since dedicated
>> RPS lock was added in:
>>
>>     commit 4fc688ce79772496503d22263d61b071a8fb596e
>>     Author: Jesse Barnes <jbarnes@virtuousgeek.org>
>>     Date:   Fri Nov 2 11:14:01 2012 -0700
>>
>>         drm/i915: protect RPS/RC6 related accesses (including PCU) with a new mutex
>>
>> Based on prototype patch by Chris Wilson and a subsequent
>> mailing list discussion involving Ville, Imre, Chris and
>> Daniel.
>>
>> v2: More details in the commit.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Imre Deak <imre.deak@intel.com>
>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>> ---
>>   drivers/gpu/drm/i915/intel_display.c | 4 ----
>>   drivers/gpu/drm/i915/intel_pm.c      | 9 +++++----
>>   2 files changed, 5 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>> index 5018295cd92b..af0d33a3697a 100644
>> --- a/drivers/gpu/drm/i915/intel_display.c
>> +++ b/drivers/gpu/drm/i915/intel_display.c
>> @@ -15995,9 +15995,7 @@ void intel_modeset_gem_init(struct drm_device *dev)
>>   	struct drm_i915_gem_object *obj;
>>   	int ret;
>>
>> -	mutex_lock(&dev->struct_mutex);
>>   	intel_init_gt_powersave(dev);
>> -	mutex_unlock(&dev->struct_mutex);
>>
>>   	intel_modeset_init_hw(dev);
>>
>> @@ -16077,9 +16075,7 @@ void intel_modeset_cleanup(struct drm_device *dev)
>>
>>   	intel_cleanup_overlay(dev);
>>
>> -	mutex_lock(&dev->struct_mutex);
>>   	intel_cleanup_gt_powersave(dev);
>> -	mutex_unlock(&dev->struct_mutex);
>
> The whitespace no longer conveys meaning, it used to be to clearly mark
> the mutex section.

Guess I can remove more lines of code and get credits for that. :D

>> @@ -5235,6 +5233,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
>>   out:
>>   	DRM_DEBUG_DRIVER("PCBR: 0x%08x\n", I915_READ(VLV_PCBR));
>>   	dev_priv->vlv_pctx = pctx;
>> +	mutex_unlock(&dev->struct_mutex);
>>   }
>>
>>   static void valleyview_cleanup_pctx(struct drm_device *dev)
>> @@ -5244,8 +5243,10 @@ static void valleyview_cleanup_pctx(struct drm_device *dev)
>>   	if (WARN_ON(!dev_priv->vlv_pctx))
>>   		return;
>>
>> +	mutex_lock(&dev->struct_mutex);
>>   	drm_gem_object_unreference(&dev_priv->vlv_pctx->base);
>>   	dev_priv->vlv_pctx = NULL;
>> +	mutex_unlock(&dev->struct_mutex);
>
> This made me smile.

Yeah mechanical- want unreference_unlocked instead?

Regards,

Tvrtko
Chris Wilson Feb. 2, 2016, 2:48 p.m. UTC | #3
On Tue, Feb 02, 2016 at 02:13:43PM +0000, Tvrtko Ursulin wrote:
> 
> On 02/02/16 13:16, Chris Wilson wrote:
> >On Tue, Feb 02, 2016 at 11:06:26AM +0000, Tvrtko Ursulin wrote:
> >>@@ -5244,8 +5243,10 @@ static void valleyview_cleanup_pctx(struct drm_device *dev)
> >>  	if (WARN_ON(!dev_priv->vlv_pctx))
> >>  		return;
> >>
> >>+	mutex_lock(&dev->struct_mutex);
> >>  	drm_gem_object_unreference(&dev_priv->vlv_pctx->base);
> >>  	dev_priv->vlv_pctx = NULL;
> >>+	mutex_unlock(&dev->struct_mutex);
> >
> >This made me smile.
> 
> Yeah mechanical- want unreference_unlocked instead?

_unlocked() has the advantage of not suggesting that dev_priv->vlv_pctx
needs to be part of the locked transaction (that's the bit that caused a
double take).

But it really doesn't matter.
-Chris

Patch
diff mbox

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 5018295cd92b..af0d33a3697a 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -15995,9 +15995,7 @@  void intel_modeset_gem_init(struct drm_device *dev)
 	struct drm_i915_gem_object *obj;
 	int ret;
 
-	mutex_lock(&dev->struct_mutex);
 	intel_init_gt_powersave(dev);
-	mutex_unlock(&dev->struct_mutex);
 
 	intel_modeset_init_hw(dev);
 
@@ -16077,9 +16075,7 @@  void intel_modeset_cleanup(struct drm_device *dev)
 
 	intel_cleanup_overlay(dev);
 
-	mutex_lock(&dev->struct_mutex);
 	intel_cleanup_gt_powersave(dev);
-	mutex_unlock(&dev->struct_mutex);
 
 	intel_teardown_gmbus(dev);
 }
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 31bc4ea395ac..7f137a70b6ae 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -5175,8 +5175,6 @@  static void cherryview_setup_pctx(struct drm_device *dev)
 	u32 pcbr;
 	int pctx_size = 32*1024;
 
-	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
-
 	pcbr = I915_READ(VLV_PCBR);
 	if ((pcbr >> VLV_PCBR_ADDR_SHIFT) == 0) {
 		DRM_DEBUG_DRIVER("BIOS didn't set up PCBR, fixing up\n");
@@ -5198,7 +5196,7 @@  static void valleyview_setup_pctx(struct drm_device *dev)
 	u32 pcbr;
 	int pctx_size = 24*1024;
 
-	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
+	mutex_lock(&dev->struct_mutex);
 
 	pcbr = I915_READ(VLV_PCBR);
 	if (pcbr) {
@@ -5226,7 +5224,7 @@  static void valleyview_setup_pctx(struct drm_device *dev)
 	pctx = i915_gem_object_create_stolen(dev, pctx_size);
 	if (!pctx) {
 		DRM_DEBUG("not enough stolen space for PCTX, disabling\n");
-		return;
+		goto out;
 	}
 
 	pctx_paddr = dev_priv->mm.stolen_base + pctx->stolen->start;
@@ -5235,6 +5233,7 @@  static void valleyview_setup_pctx(struct drm_device *dev)
 out:
 	DRM_DEBUG_DRIVER("PCBR: 0x%08x\n", I915_READ(VLV_PCBR));
 	dev_priv->vlv_pctx = pctx;
+	mutex_unlock(&dev->struct_mutex);
 }
 
 static void valleyview_cleanup_pctx(struct drm_device *dev)
@@ -5244,8 +5243,10 @@  static void valleyview_cleanup_pctx(struct drm_device *dev)
 	if (WARN_ON(!dev_priv->vlv_pctx))
 		return;
 
+	mutex_lock(&dev->struct_mutex);
 	drm_gem_object_unreference(&dev_priv->vlv_pctx->base);
 	dev_priv->vlv_pctx = NULL;
+	mutex_unlock(&dev->struct_mutex);
 }
 
 static void valleyview_init_gt_powersave(struct drm_device *dev)