[PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

We had three failure modes here:

1.
Deadlock in intelfb_alloc failure path where it calls
drm_framebuffer_remove, which grabs the struct mutex and intelfb_create
(caller of intelfb_alloc) was already holding it.

2.
Double unreference on the object if __intel_framebuffer_create fails
since both it and the caller (intelfb_alloc) do the unreference.

3.
Deadlock in intelfb_create failure path where it calls
drm_framebuffer_unreference, which grabs the struct mutex and
intelfb_create was already holding it.

v2:
   * Reformat commit msg to 72 chars. (Lukas Wunner)
   * Added third failure mode. (Lukas Wunner)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: 60a5ca015ffd2aacfe5674b5a401cd2a37159e07
Reported-By: Lukas Wunner <lukas@wunner.de>
Tested-By: Lukas Wunner <lukas@wunner.de>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Lukas Wunner <lukas@wunner.de>
---
Ville, you suggested some changes earlier;

"""
I suggest removing the unref from __intel_framebuffer_create().
"""

Do you view that as an improvement in code clarity/organisation,
or you think my version is actually wrong for some reason?
---
 drivers/gpu/drm/i915/intel_fbdev.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index 2a1724e..118420b 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -141,7 +141,7 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 {
 	struct intel_fbdev *ifbdev =
 		container_of(helper, struct intel_fbdev, helper);
-	struct drm_framebuffer *fb;
+	struct drm_framebuffer *fb = NULL;
 	struct drm_device *dev = helper->dev;
 	struct drm_mode_fb_cmd2 mode_cmd = {};
 	struct drm_i915_gem_object *obj;
@@ -159,6 +159,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
 							  sizes->surface_depth);
 
+	mutex_lock(&dev->struct_mutex);
+
 	size = mode_cmd.pitches[0] * mode_cmd.height;
 	size = PAGE_ALIGN(size);
 	obj = i915_gem_object_create_stolen(dev, size);
@@ -172,8 +174,9 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 
 	fb = __intel_framebuffer_create(dev, &mode_cmd, obj);
 	if (IS_ERR(fb)) {
+		/* Drops object reference on failure. */
 		ret = PTR_ERR(fb);
-		goto out_unref;
+		goto out;
 	}
 
 	/* Flush everything out, we'll be doing GTT only from now on */
@@ -183,15 +186,18 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 		goto out_fb;
 	}
 
+	mutex_unlock(&dev->struct_mutex);
+
 	ifbdev->fb = to_intel_framebuffer(fb);
 
 	return 0;
 
 out_fb:
-	drm_framebuffer_remove(fb);
-out_unref:
 	drm_gem_object_unreference(&obj->base);
 out:
+	mutex_unlock(&dev->struct_mutex);
+	if (fb)
+		drm_framebuffer_remove(fb);
 	return ret;
 }
 
@@ -209,8 +215,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
 	int size, ret;
 	bool prealloc = false;
 
-	mutex_lock(&dev->struct_mutex);
-
 	if (intel_fb &&
 	    (sizes->fb_width > intel_fb->base.width ||
 	     sizes->fb_height > intel_fb->base.height)) {
@@ -225,7 +229,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
 		DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
 		ret = intelfb_alloc(helper, sizes);
 		if (ret)
-			goto out_unlock;
+			return ret;
 		intel_fb = ifbdev->fb;
 	} else {
 		DRM_DEBUG_KMS("re-using BIOS fb\n");
@@ -237,6 +241,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
 	obj = intel_fb->obj;
 	size = obj->base.size;
 
+	mutex_lock(&dev->struct_mutex);
+
 	info = framebuffer_alloc(0, &dev->pdev->dev);
 	if (!info) {
 		ret = -ENOMEM;
@@ -307,7 +313,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
 out_unpin:
 	i915_gem_object_ggtt_unpin(obj);
 	drm_gem_object_unreference(&obj->base);
-out_unlock:
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
-- 
2.4.2

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[PATCH v3 1/2] drm/i915: Fix failure paths around initial fbdev allocation

[Lukas Wunner]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

We had two failure modes here:

1.
Deadlock in intelfb_alloc failure path where it calls
drm_framebuffer_remove, which grabs the struct mutex and intelfb_create
(caller of intelfb_alloc) was already holding it.

2.
Deadlock in intelfb_create failure path where it calls
drm_framebuffer_unreference, which grabs the struct mutex and
intelfb_create was already holding it.

v2:
   * Reformat commit msg to 72 chars. (Lukas Wunner)
   * Add third failure mode. (Lukas Wunner)

v3:
   * On fb alloc failure, unref gem object where it gets refed,
     fix double unref in separate commit. (Ville Syrjälä)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: 60a5ca015ffd ("drm/i915: Add locking around
    framebuffer_references--")
Reported-By: Lukas Wunner <lukas@wunner.de>
Tested-By: Lukas Wunner <lukas@wunner.de>
[Lukas: Create v3 based on Tvrtko's v2]
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_fbdev.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index 4e7e7da..bce2f73 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -115,7 +115,7 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 {
 	struct intel_fbdev *ifbdev =
 		container_of(helper, struct intel_fbdev, helper);
-	struct drm_framebuffer *fb;
+	struct drm_framebuffer *fb = NULL;
 	struct drm_device *dev = helper->dev;
 	struct drm_mode_fb_cmd2 mode_cmd = {};
 	struct drm_i915_gem_object *obj;
@@ -133,6 +133,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
 							  sizes->surface_depth);
 
+	mutex_lock(&dev->struct_mutex);
+
 	size = mode_cmd.pitches[0] * mode_cmd.height;
 	size = PAGE_ALIGN(size);
 	obj = i915_gem_object_create_stolen(dev, size);
@@ -154,18 +156,21 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 	ret = intel_pin_and_fence_fb_obj(NULL, fb, NULL, NULL);
 	if (ret) {
 		DRM_ERROR("failed to pin obj: %d\n", ret);
-		goto out_fb;
+		goto out_unref;
 	}
 
+	mutex_unlock(&dev->struct_mutex);
+
 	ifbdev->fb = to_intel_framebuffer(fb);
 
 	return 0;
 
-out_fb:
-	drm_framebuffer_remove(fb);
 out_unref:
 	drm_gem_object_unreference(&obj->base);
 out:
+	mutex_unlock(&dev->struct_mutex);
+	if (fb)
+		drm_framebuffer_remove(fb);
 	return ret;
 }
 
@@ -183,8 +188,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
 	int size, ret;
 	bool prealloc = false;
 
-	mutex_lock(&dev->struct_mutex);
-
 	if (intel_fb &&
 	    (sizes->fb_width > intel_fb->base.width ||
 	     sizes->fb_height > intel_fb->base.height)) {
@@ -199,7 +202,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
 		DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
 		ret = intelfb_alloc(helper, sizes);
 		if (ret)
-			goto out_unlock;
+			return ret;
 		intel_fb = ifbdev->fb;
 	} else {
 		DRM_DEBUG_KMS("re-using BIOS fb\n");
@@ -211,6 +214,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
 	obj = intel_fb->obj;
 	size = obj->base.size;
 
+	mutex_lock(&dev->struct_mutex);
+
 	info = framebuffer_alloc(0, &dev->pdev->dev);
 	if (!info) {
 		ret = -ENOMEM;
@@ -281,7 +286,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
 out_unpin:
 	i915_gem_object_ggtt_unpin(obj);
 	drm_gem_object_unreference(&obj->base);
-out_unlock:
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
-- 
2.1.0

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[PATCH v4 1/2] drm/i915: Fix failure paths around initial fbdev allocation

[Lukas Wunner]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

We had two failure modes here:

1.
Deadlock in intelfb_alloc failure path where it calls
drm_framebuffer_remove, which grabs the struct mutex and intelfb_create
(caller of intelfb_alloc) was already holding it.

2.
Deadlock in intelfb_create failure path where it calls
drm_framebuffer_unreference, which grabs the struct mutex and
intelfb_create was already holding it.

v2:
   * Reformat commit msg to 72 chars. (Lukas Wunner)
   * Add third failure mode. (Lukas Wunner)

v3:
   * On fb alloc failure, unref gem object where it gets refed,
     fix double unref in separate commit. (Ville Syrjälä)

v4:
   * Lock struct mutex on unref. (Chris Wilson)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: 60a5ca015ffd ("drm/i915: Add locking around
    framebuffer_references--")
Reported-By: Lukas Wunner <lukas@wunner.de>
Tested-By: Lukas Wunner <lukas@wunner.de>
[Lukas: Create v3 + v4 based on Tvrtko's v2]
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_fbdev.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index 4e7e7da..bce2f73 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -115,7 +115,7 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 {
 	struct intel_fbdev *ifbdev =
 		container_of(helper, struct intel_fbdev, helper);
-	struct drm_framebuffer *fb;
+	struct drm_framebuffer *fb = NULL;
 	struct drm_device *dev = helper->dev;
 	struct drm_mode_fb_cmd2 mode_cmd = {};
 	struct drm_i915_gem_object *obj;
@@ -133,6 +133,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
 							  sizes->surface_depth);
 
+	mutex_lock(&dev->struct_mutex);
+
 	size = mode_cmd.pitches[0] * mode_cmd.height;
 	size = PAGE_ALIGN(size);
 	obj = i915_gem_object_create_stolen(dev, size);
@@ -154,18 +156,21 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 	ret = intel_pin_and_fence_fb_obj(NULL, fb, NULL, NULL);
 	if (ret) {
 		DRM_ERROR("failed to pin obj: %d\n", ret);
-		goto out_fb;
+		goto out_unref;
 	}
 
+	mutex_unlock(&dev->struct_mutex);
+
 	ifbdev->fb = to_intel_framebuffer(fb);
 
 	return 0;
 
-out_fb:
-	drm_framebuffer_remove(fb);
 out_unref:
 	drm_gem_object_unreference(&obj->base);
 out:
+	mutex_unlock(&dev->struct_mutex);
+	if (fb)
+		drm_framebuffer_remove(fb);
 	return ret;
 }
 
@@ -183,8 +188,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
 	int size, ret;
 	bool prealloc = false;
 
-	mutex_lock(&dev->struct_mutex);
-
 	if (intel_fb &&
 	    (sizes->fb_width > intel_fb->base.width ||
 	     sizes->fb_height > intel_fb->base.height)) {
@@ -199,7 +202,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
 		DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
 		ret = intelfb_alloc(helper, sizes);
 		if (ret)
-			goto out_unlock;
+			return ret;
 		intel_fb = ifbdev->fb;
 	} else {
 		DRM_DEBUG_KMS("re-using BIOS fb\n");
@@ -211,6 +214,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
 	obj = intel_fb->obj;
 	size = obj->base.size;
 
+	mutex_lock(&dev->struct_mutex);
+
 	info = framebuffer_alloc(0, &dev->pdev->dev);
 	if (!info) {
 		ret = -ENOMEM;
@@ -281,7 +286,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
 out_unpin:
 	i915_gem_object_ggtt_unpin(obj);
 	drm_gem_object_unreference(&obj->base);
-out_unlock:
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
-- 
2.1.0

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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[shuang.he]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he@intel.com)
Task id: 6642
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
ILK                                  302/302              302/302
SNB                                  312/316              312/316
IVB                                  343/343              343/343
BYT                 -1              287/287              286/287
HSW                                  380/380              380/380
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*BYT  igt@gem_tiled_partial_pwrite_pread@reads      PASS(1)      FAIL(1)
Note: You need to pay more attention to line start with '*'
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Jani Nikula]

On Tue, 30 Jun 2015, Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com> wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>
> We had three failure modes here:
>
> 1.
> Deadlock in intelfb_alloc failure path where it calls
> drm_framebuffer_remove, which grabs the struct mutex and intelfb_create
> (caller of intelfb_alloc) was already holding it.
>
> 2.
> Double unreference on the object if __intel_framebuffer_create fails
> since both it and the caller (intelfb_alloc) do the unreference.
>
> 3.
> Deadlock in intelfb_create failure path where it calls
> drm_framebuffer_unreference, which grabs the struct mutex and
> intelfb_create was already holding it.
>
> v2:
>    * Reformat commit msg to 72 chars. (Lukas Wunner)
>    * Added third failure mode. (Lukas Wunner)
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Fixes: 60a5ca015ffd2aacfe5674b5a401cd2a37159e07

The format is

Fixes: 60a5ca015ffd ("drm/i915: Add locking around framebuffer_references--")

See Documentation/SubmittingPatches on how to have git output that
format for you.

BR,
Jani.



> Reported-By: Lukas Wunner <lukas@wunner.de>
> Tested-By: Lukas Wunner <lukas@wunner.de>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Lukas Wunner <lukas@wunner.de>
> ---
> Ville, you suggested some changes earlier;
>
> """
> I suggest removing the unref from __intel_framebuffer_create().
> """
>
> Do you view that as an improvement in code clarity/organisation,
> or you think my version is actually wrong for some reason?
> ---
>  drivers/gpu/drm/i915/intel_fbdev.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 2a1724e..118420b 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -141,7 +141,7 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  {
>  	struct intel_fbdev *ifbdev =
>  		container_of(helper, struct intel_fbdev, helper);
> -	struct drm_framebuffer *fb;
> +	struct drm_framebuffer *fb = NULL;
>  	struct drm_device *dev = helper->dev;
>  	struct drm_mode_fb_cmd2 mode_cmd = {};
>  	struct drm_i915_gem_object *obj;
> @@ -159,6 +159,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
>  							  sizes->surface_depth);
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	size = mode_cmd.pitches[0] * mode_cmd.height;
>  	size = PAGE_ALIGN(size);
>  	obj = i915_gem_object_create_stolen(dev, size);
> @@ -172,8 +174,9 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  
>  	fb = __intel_framebuffer_create(dev, &mode_cmd, obj);
>  	if (IS_ERR(fb)) {
> +		/* Drops object reference on failure. */
>  		ret = PTR_ERR(fb);
> -		goto out_unref;
> +		goto out;
>  	}
>  
>  	/* Flush everything out, we'll be doing GTT only from now on */
> @@ -183,15 +186,18 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  		goto out_fb;
>  	}
>  
> +	mutex_unlock(&dev->struct_mutex);
> +
>  	ifbdev->fb = to_intel_framebuffer(fb);
>  
>  	return 0;
>  
>  out_fb:
> -	drm_framebuffer_remove(fb);
> -out_unref:
>  	drm_gem_object_unreference(&obj->base);
>  out:
> +	mutex_unlock(&dev->struct_mutex);
> +	if (fb)
> +		drm_framebuffer_remove(fb);
>  	return ret;
>  }
>  
> @@ -209,8 +215,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	int size, ret;
>  	bool prealloc = false;
>  
> -	mutex_lock(&dev->struct_mutex);
> -
>  	if (intel_fb &&
>  	    (sizes->fb_width > intel_fb->base.width ||
>  	     sizes->fb_height > intel_fb->base.height)) {
> @@ -225,7 +229,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  		DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
>  		ret = intelfb_alloc(helper, sizes);
>  		if (ret)
> -			goto out_unlock;
> +			return ret;
>  		intel_fb = ifbdev->fb;
>  	} else {
>  		DRM_DEBUG_KMS("re-using BIOS fb\n");
> @@ -237,6 +241,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	obj = intel_fb->obj;
>  	size = obj->base.size;
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	info = framebuffer_alloc(0, &dev->pdev->dev);
>  	if (!info) {
>  		ret = -ENOMEM;
> @@ -307,7 +313,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  out_unpin:
>  	i915_gem_object_ggtt_unpin(obj);
>  	drm_gem_object_unreference(&obj->base);
> -out_unlock:
>  	mutex_unlock(&dev->struct_mutex);
>  	return ret;
>  }
> -- 
> 2.4.2
>
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Jani Nikula, Intel Open Source Technology Center
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Lukas Wunner]

Hi,

not sure if another reaction from me is required, but in case there is:
The patch as quoted below LGTM now, so unless Ville vetoes because of
his suggestion (see below) I think this is ready for inclusion in 4.2.

Thanks,

Lukas

On Tue, Jun 30, 2015 at 10:06:27AM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> We had three failure modes here:
> 
> 1.
> Deadlock in intelfb_alloc failure path where it calls
> drm_framebuffer_remove, which grabs the struct mutex and intelfb_create
> (caller of intelfb_alloc) was already holding it.
> 
> 2.
> Double unreference on the object if __intel_framebuffer_create fails
> since both it and the caller (intelfb_alloc) do the unreference.
> 
> 3.
> Deadlock in intelfb_create failure path where it calls
> drm_framebuffer_unreference, which grabs the struct mutex and
> intelfb_create was already holding it.
> 
> v2:
>    * Reformat commit msg to 72 chars. (Lukas Wunner)
>    * Added third failure mode. (Lukas Wunner)
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Fixes: 60a5ca015ffd2aacfe5674b5a401cd2a37159e07
> Reported-By: Lukas Wunner <lukas@wunner.de>
> Tested-By: Lukas Wunner <lukas@wunner.de>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Lukas Wunner <lukas@wunner.de>
> ---
> Ville, you suggested some changes earlier;
> 
> """
> I suggest removing the unref from __intel_framebuffer_create().
> """
> 
> Do you view that as an improvement in code clarity/organisation,
> or you think my version is actually wrong for some reason?
> ---
>  drivers/gpu/drm/i915/intel_fbdev.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 2a1724e..118420b 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -141,7 +141,7 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  {
>  	struct intel_fbdev *ifbdev =
>  		container_of(helper, struct intel_fbdev, helper);
> -	struct drm_framebuffer *fb;
> +	struct drm_framebuffer *fb = NULL;
>  	struct drm_device *dev = helper->dev;
>  	struct drm_mode_fb_cmd2 mode_cmd = {};
>  	struct drm_i915_gem_object *obj;
> @@ -159,6 +159,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
>  							  sizes->surface_depth);
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	size = mode_cmd.pitches[0] * mode_cmd.height;
>  	size = PAGE_ALIGN(size);
>  	obj = i915_gem_object_create_stolen(dev, size);
> @@ -172,8 +174,9 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  
>  	fb = __intel_framebuffer_create(dev, &mode_cmd, obj);
>  	if (IS_ERR(fb)) {
> +		/* Drops object reference on failure. */
>  		ret = PTR_ERR(fb);
> -		goto out_unref;
> +		goto out;
>  	}
>  
>  	/* Flush everything out, we'll be doing GTT only from now on */
> @@ -183,15 +186,18 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  		goto out_fb;
>  	}
>  
> +	mutex_unlock(&dev->struct_mutex);
> +
>  	ifbdev->fb = to_intel_framebuffer(fb);
>  
>  	return 0;
>  
>  out_fb:
> -	drm_framebuffer_remove(fb);
> -out_unref:
>  	drm_gem_object_unreference(&obj->base);
>  out:
> +	mutex_unlock(&dev->struct_mutex);
> +	if (fb)
> +		drm_framebuffer_remove(fb);
>  	return ret;
>  }
>  
> @@ -209,8 +215,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	int size, ret;
>  	bool prealloc = false;
>  
> -	mutex_lock(&dev->struct_mutex);
> -
>  	if (intel_fb &&
>  	    (sizes->fb_width > intel_fb->base.width ||
>  	     sizes->fb_height > intel_fb->base.height)) {
> @@ -225,7 +229,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  		DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
>  		ret = intelfb_alloc(helper, sizes);
>  		if (ret)
> -			goto out_unlock;
> +			return ret;
>  		intel_fb = ifbdev->fb;
>  	} else {
>  		DRM_DEBUG_KMS("re-using BIOS fb\n");
> @@ -237,6 +241,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	obj = intel_fb->obj;
>  	size = obj->base.size;
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	info = framebuffer_alloc(0, &dev->pdev->dev);
>  	if (!info) {
>  		ret = -ENOMEM;
> @@ -307,7 +313,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  out_unpin:
>  	i915_gem_object_ggtt_unpin(obj);
>  	drm_gem_object_unreference(&obj->base);
> -out_unlock:
>  	mutex_unlock(&dev->struct_mutex);
>  	return ret;
>  }
> -- 
> 2.4.2
> 
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Ville Syrjälä]

On Tue, Jun 30, 2015 at 10:06:27AM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> We had three failure modes here:
> 
> 1.
> Deadlock in intelfb_alloc failure path where it calls
> drm_framebuffer_remove, which grabs the struct mutex and intelfb_create
> (caller of intelfb_alloc) was already holding it.
> 
> 2.
> Double unreference on the object if __intel_framebuffer_create fails
> since both it and the caller (intelfb_alloc) do the unreference.
> 
> 3.
> Deadlock in intelfb_create failure path where it calls
> drm_framebuffer_unreference, which grabs the struct mutex and
> intelfb_create was already holding it.
> 
> v2:
>    * Reformat commit msg to 72 chars. (Lukas Wunner)
>    * Added third failure mode. (Lukas Wunner)
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Fixes: 60a5ca015ffd2aacfe5674b5a401cd2a37159e07
> Reported-By: Lukas Wunner <lukas@wunner.de>
> Tested-By: Lukas Wunner <lukas@wunner.de>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Lukas Wunner <lukas@wunner.de>
> ---
> Ville, you suggested some changes earlier;
> 
> """
> I suggest removing the unref from __intel_framebuffer_create().
> """
> 
> Do you view that as an improvement in code clarity/organisation,
> or you think my version is actually wrong for some reason?

I find it rather unexpected that the function drops the passed
reference on error. My usual rule is: do nothing on error, if possible.

> ---
>  drivers/gpu/drm/i915/intel_fbdev.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 2a1724e..118420b 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -141,7 +141,7 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  {
>  	struct intel_fbdev *ifbdev =
>  		container_of(helper, struct intel_fbdev, helper);
> -	struct drm_framebuffer *fb;
> +	struct drm_framebuffer *fb = NULL;
>  	struct drm_device *dev = helper->dev;
>  	struct drm_mode_fb_cmd2 mode_cmd = {};
>  	struct drm_i915_gem_object *obj;
> @@ -159,6 +159,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
>  							  sizes->surface_depth);
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	size = mode_cmd.pitches[0] * mode_cmd.height;
>  	size = PAGE_ALIGN(size);
>  	obj = i915_gem_object_create_stolen(dev, size);
> @@ -172,8 +174,9 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  
>  	fb = __intel_framebuffer_create(dev, &mode_cmd, obj);
>  	if (IS_ERR(fb)) {
> +		/* Drops object reference on failure. */
>  		ret = PTR_ERR(fb);
> -		goto out_unref;
> +		goto out;
>  	}
>  
>  	/* Flush everything out, we'll be doing GTT only from now on */
> @@ -183,15 +186,18 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  		goto out_fb;
>  	}
>  
> +	mutex_unlock(&dev->struct_mutex);
> +
>  	ifbdev->fb = to_intel_framebuffer(fb);
>  
>  	return 0;
>  
>  out_fb:
> -	drm_framebuffer_remove(fb);
> -out_unref:
>  	drm_gem_object_unreference(&obj->base);
>  out:
> +	mutex_unlock(&dev->struct_mutex);
> +	if (fb)
> +		drm_framebuffer_remove(fb);
>  	return ret;
>  }
>  
> @@ -209,8 +215,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	int size, ret;
>  	bool prealloc = false;
>  
> -	mutex_lock(&dev->struct_mutex);
> -
>  	if (intel_fb &&
>  	    (sizes->fb_width > intel_fb->base.width ||
>  	     sizes->fb_height > intel_fb->base.height)) {
> @@ -225,7 +229,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  		DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
>  		ret = intelfb_alloc(helper, sizes);
>  		if (ret)
> -			goto out_unlock;
> +			return ret;
>  		intel_fb = ifbdev->fb;
>  	} else {
>  		DRM_DEBUG_KMS("re-using BIOS fb\n");
> @@ -237,6 +241,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	obj = intel_fb->obj;
>  	size = obj->base.size;
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	info = framebuffer_alloc(0, &dev->pdev->dev);
>  	if (!info) {
>  		ret = -ENOMEM;
> @@ -307,7 +313,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  out_unpin:
>  	i915_gem_object_ggtt_unpin(obj);
>  	drm_gem_object_unreference(&obj->base);
> -out_unlock:
>  	mutex_unlock(&dev->struct_mutex);
>  	return ret;
>  }
> -- 
> 2.4.2

-- 
Ville Syrjälä
Intel OTC
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Tvrtko Ursulin]

On 07/02/2015 02:37 PM, Ville Syrjälä wrote:
> On Tue, Jun 30, 2015 at 10:06:27AM +0100, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> We had three failure modes here:
>>
>> 1.
>> Deadlock in intelfb_alloc failure path where it calls
>> drm_framebuffer_remove, which grabs the struct mutex and intelfb_create
>> (caller of intelfb_alloc) was already holding it.
>>
>> 2.
>> Double unreference on the object if __intel_framebuffer_create fails
>> since both it and the caller (intelfb_alloc) do the unreference.
>>
>> 3.
>> Deadlock in intelfb_create failure path where it calls
>> drm_framebuffer_unreference, which grabs the struct mutex and
>> intelfb_create was already holding it.
>>
>> v2:
>>     * Reformat commit msg to 72 chars. (Lukas Wunner)
>>     * Added third failure mode. (Lukas Wunner)
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>> Fixes: 60a5ca015ffd2aacfe5674b5a401cd2a37159e07
>> Reported-By: Lukas Wunner <lukas@wunner.de>
>> Tested-By: Lukas Wunner <lukas@wunner.de>
>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Lukas Wunner <lukas@wunner.de>
>> ---
>> Ville, you suggested some changes earlier;
>>
>> """
>> I suggest removing the unref from __intel_framebuffer_create().
>> """
>>
>> Do you view that as an improvement in code clarity/organisation,
>> or you think my version is actually wrong for some reason?
>
> I find it rather unexpected that the function drops the passed
> reference on error. My usual rule is: do nothing on error, if possible.

I just don't have time at the moment to evaluate the other call sites 
etc. So from my point of view it boils down to whether this patch 
improves things without making anything worse. If it does R-B would be 
cool. If it doesn't then it will have to make for free time to appear. 
Or someone is free to take it over.

Regards,

Tvrtko
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[PATCH v3 2/2] drm/i915: On fb alloc failure, unref gem object where it gets refed

[Lukas Wunner]

Currently when allocating a framebuffer fails, the gem object gets
unrefed at the bottom of the call chain in __intel_framebuffer_create,
not where it gets refed, which is in intel_framebuffer_create_for_mode
(via i915_gem_alloc_object) and in intel_user_framebuffer_create
(via drm_gem_object_lookup).

This invites mistakes: As discovered by Tvrtko Ursulin, a double unref
has sneaked into intelfb_alloc (which calls __intel_framebuffer_create).

As suggested by Ville Syrjälä, improve code clarity by moving the unref
away from __intel_framebuffer_create to where the gem object gets refed.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Fixes: a8bb6818270c ("drm/i915: Fix error path leak in fbdev fb
    allocation")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/intel_display.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 9079fcd..9499003 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8876,20 +8876,17 @@ __intel_framebuffer_create(struct drm_device *dev,
 	int ret;
 
 	intel_fb = kzalloc(sizeof(*intel_fb), GFP_KERNEL);
-	if (!intel_fb) {
-		drm_gem_object_unreference(&obj->base);
+	if (!intel_fb)
 		return ERR_PTR(-ENOMEM);
-	}
 
 	ret = intel_framebuffer_init(dev, intel_fb, mode_cmd, obj);
 	if (ret)
 		goto err;
 
 	return &intel_fb->base;
+
 err:
-	drm_gem_object_unreference(&obj->base);
 	kfree(intel_fb);
-
 	return ERR_PTR(ret);
 }
 
@@ -8929,6 +8926,7 @@ intel_framebuffer_create_for_mode(struct drm_device *dev,
 				  struct drm_display_mode *mode,
 				  int depth, int bpp)
 {
+	struct drm_framebuffer *fb;
 	struct drm_i915_gem_object *obj;
 	struct drm_mode_fb_cmd2 mode_cmd = { 0 };
 
@@ -8943,7 +8941,11 @@ intel_framebuffer_create_for_mode(struct drm_device *dev,
 								bpp);
 	mode_cmd.pixel_format = drm_mode_legacy_fb_format(bpp, depth);
 
-	return intel_framebuffer_create(dev, &mode_cmd, obj);
+	fb = intel_framebuffer_create(dev, &mode_cmd, obj);
+	if (IS_ERR(fb))
+		drm_gem_object_unreference(&obj->base);
+
+	return fb;
 }
 
 static struct drm_framebuffer *
@@ -13379,6 +13381,7 @@ intel_user_framebuffer_create(struct drm_device *dev,
 			      struct drm_file *filp,
 			      struct drm_mode_fb_cmd2 *mode_cmd)
 {
+	struct drm_framebuffer *fb;
 	struct drm_i915_gem_object *obj;
 
 	obj = to_intel_bo(drm_gem_object_lookup(dev, filp,
@@ -13386,7 +13389,11 @@ intel_user_framebuffer_create(struct drm_device *dev,
 	if (&obj->base == NULL)
 		return ERR_PTR(-ENOENT);
 
-	return intel_framebuffer_create(dev, mode_cmd, obj);
+	fb = intel_framebuffer_create(dev, mode_cmd, obj);
+	if (IS_ERR(fb))
+		drm_gem_object_unreference(&obj->base);
+
+	return fb;
 }
 
 static void intel_output_poll_changed(struct drm_device *dev)
-- 
2.1.0

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[PATCH v4 2/2] drm/i915: On fb alloc failure, unref gem object where it gets refed

[Lukas Wunner]

Currently when allocating a framebuffer fails, the gem object gets
unrefed at the bottom of the call chain in __intel_framebuffer_create,
not where it gets refed, which is in intel_framebuffer_create_for_mode
(via i915_gem_alloc_object) and in intel_user_framebuffer_create
(via drm_gem_object_lookup).

This invites mistakes: As discovered by Tvrtko Ursulin, a double unref
has sneaked into intelfb_alloc (which calls __intel_framebuffer_create).

As suggested by Ville Syrjälä, improve code clarity by moving the unref
away from __intel_framebuffer_create to where the gem object gets refed.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Fixes: a8bb6818270c ("drm/i915: Fix error path leak in fbdev fb
    allocation")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_display.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 9079fcd..d597afa 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8876,20 +8876,17 @@ __intel_framebuffer_create(struct drm_device *dev,
 	int ret;
 
 	intel_fb = kzalloc(sizeof(*intel_fb), GFP_KERNEL);
-	if (!intel_fb) {
-		drm_gem_object_unreference(&obj->base);
+	if (!intel_fb)
 		return ERR_PTR(-ENOMEM);
-	}
 
 	ret = intel_framebuffer_init(dev, intel_fb, mode_cmd, obj);
 	if (ret)
 		goto err;
 
 	return &intel_fb->base;
+
 err:
-	drm_gem_object_unreference(&obj->base);
 	kfree(intel_fb);
-
 	return ERR_PTR(ret);
 }
 
@@ -8929,6 +8926,7 @@ intel_framebuffer_create_for_mode(struct drm_device *dev,
 				  struct drm_display_mode *mode,
 				  int depth, int bpp)
 {
+	struct drm_framebuffer *fb;
 	struct drm_i915_gem_object *obj;
 	struct drm_mode_fb_cmd2 mode_cmd = { 0 };
 
@@ -8943,7 +8941,11 @@ intel_framebuffer_create_for_mode(struct drm_device *dev,
 								bpp);
 	mode_cmd.pixel_format = drm_mode_legacy_fb_format(bpp, depth);
 
-	return intel_framebuffer_create(dev, &mode_cmd, obj);
+	fb = intel_framebuffer_create(dev, &mode_cmd, obj);
+	if (IS_ERR(fb))
+		drm_gem_object_unreference_unlocked(&obj->base);
+
+	return fb;
 }
 
 static struct drm_framebuffer *
@@ -13379,6 +13381,7 @@ intel_user_framebuffer_create(struct drm_device *dev,
 			      struct drm_file *filp,
 			      struct drm_mode_fb_cmd2 *mode_cmd)
 {
+	struct drm_framebuffer *fb;
 	struct drm_i915_gem_object *obj;
 
 	obj = to_intel_bo(drm_gem_object_lookup(dev, filp,
@@ -13386,7 +13389,11 @@ intel_user_framebuffer_create(struct drm_device *dev,
 	if (&obj->base == NULL)
 		return ERR_PTR(-ENOENT);
 
-	return intel_framebuffer_create(dev, mode_cmd, obj);
+	fb = intel_framebuffer_create(dev, mode_cmd, obj);
+	if (IS_ERR(fb))
+		drm_gem_object_unreference_unlocked(&obj->base);
+
+	return fb;
 }
 
 static void intel_output_poll_changed(struct drm_device *dev)
-- 
2.1.0

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Re: [PATCH v3 2/2] drm/i915: On fb alloc failure, unref gem object where it gets refed

[Chris Wilson]

On Sat, Jul 04, 2015 at 11:50:58AM +0200, Lukas Wunner wrote:
> Currently when allocating a framebuffer fails, the gem object gets
> unrefed at the bottom of the call chain in __intel_framebuffer_create,
> not where it gets refed, which is in intel_framebuffer_create_for_mode
> (via i915_gem_alloc_object) and in intel_user_framebuffer_create
> (via drm_gem_object_lookup).
> 
> This invites mistakes: As discovered by Tvrtko Ursulin, a double unref
> has sneaked into intelfb_alloc (which calls __intel_framebuffer_create).
> 
> As suggested by Ville Syrjälä, improve code clarity by moving the unref
> away from __intel_framebuffer_create to where the gem object gets refed.
> 
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> Fixes: a8bb6818270c ("drm/i915: Fix error path leak in fbdev fb
>     allocation")
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_display.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 9079fcd..9499003 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -8876,20 +8876,17 @@ __intel_framebuffer_create(struct drm_device *dev,
>  	int ret;
>  
>  	intel_fb = kzalloc(sizeof(*intel_fb), GFP_KERNEL);
> -	if (!intel_fb) {
> -		drm_gem_object_unreference(&obj->base);
> +	if (!intel_fb)
>  		return ERR_PTR(-ENOMEM);
> -	}
>  
>  	ret = intel_framebuffer_init(dev, intel_fb, mode_cmd, obj);
>  	if (ret)
>  		goto err;
>  
>  	return &intel_fb->base;
> +
>  err:
> -	drm_gem_object_unreference(&obj->base);
>  	kfree(intel_fb);
> -
>  	return ERR_PTR(ret);
>  }
>  
> @@ -8929,6 +8926,7 @@ intel_framebuffer_create_for_mode(struct drm_device *dev,
>  				  struct drm_display_mode *mode,
>  				  int depth, int bpp)
>  {
> +	struct drm_framebuffer *fb;
>  	struct drm_i915_gem_object *obj;
>  	struct drm_mode_fb_cmd2 mode_cmd = { 0 };
>  
> @@ -8943,7 +8941,11 @@ intel_framebuffer_create_for_mode(struct drm_device *dev,
>  								bpp);
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(bpp, depth);
>  
> -	return intel_framebuffer_create(dev, &mode_cmd, obj);
> +	fb = intel_framebuffer_create(dev, &mode_cmd, obj);
> +	if (IS_ERR(fb))
> +		drm_gem_object_unreference(&obj->base);

This needs to be drm_gem_object_unreference_unlocked(). It's much
simpler if you just document this as consuming the obj reference. If you
want to fix it, you have to move the struct_mutex into the caller i.e.
eliminate intel_framebuffer_create() and call
__intel_framebuffer_create().
-Chris

-- 
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Lukas Wunner]

Hi,

On Thu, Jul 02, 2015 at 02:59:24PM +0100, Tvrtko Ursulin wrote:
> On 07/02/2015 02:37 PM, Ville Syrjälä wrote:
> >On Tue, Jun 30, 2015 at 10:06:27AM +0100, Tvrtko Ursulin wrote:
> >>Ville, you suggested some changes earlier;
> >>"""
> >>I suggest removing the unref from __intel_framebuffer_create().
> >>"""
> >>Do you view that as an improvement in code clarity/organisation,
> >>or you think my version is actually wrong for some reason?
> >I find it rather unexpected that the function drops the passed
> >reference on error. My usual rule is: do nothing on error, if possible.
> I just don't have time at the moment to evaluate the other call sites etc.
> So from my point of view it boils down to whether this patch improves things
> without making anything worse. If it does R-B would be cool. If it doesn't
> then it will have to make for free time to appear. Or someone is free to
> take it over.

I think Ville's suggestion is merited, right now the unref on failure
happens at the bottom of the call chain in __intel_framebuffer_create
while the ref happened further up in the call chain. This should really
be consolidated in the same place. That a double unref managed to sneak
into intelfb_alloc proves this is error prone.

I've just submitted a v3 which is functionally equivalent to Tvrtko's v2
but takes up Ville's suggestion. This consists of two patches now, the
first one being equivalent to Tvrtko's patch sans fix for the double unref,
the second one fixing the double unref by moving the unref further up the
call chain. Of course I've tested this, works for me.

Now you can decide for yourself which version you like better. :-)

Thanks,

Lukas
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Re: [PATCH v3 2/2] drm/i915: On fb alloc failure, unref gem object where it gets refed

[Lukas Wunner]

Hi Chris,

thank you for the quick response (on a weekend no less).


On Sat, Jul 04, 2015 at 01:31:48PM +0100, Chris Wilson wrote:
> > -	return intel_framebuffer_create(dev, &mode_cmd, obj);
> > +	fb = intel_framebuffer_create(dev, &mode_cmd, obj);
> > +	if (IS_ERR(fb))
> > +		drm_gem_object_unreference(&obj->base);
> 
> This needs to be drm_gem_object_unreference_unlocked().

You're absolutely right, thanks for pointing this out.
I'm posting a rectified v4 right now.


> It's much simpler if you just document this as consuming the
> obj reference.

Yes but I believe that is what Ville took exception to.

If you guys all agree that documenting this is sufficient then
you can just merge Tvrtko's v2. The rationale of the v3 + v4
I've submitted is to offer an alternative in the hope of pushing
this forward.


> If you want to fix it, you have to move the struct_mutex into
> the caller i.e. eliminate intel_framebuffer_create() and call
> __intel_framebuffer_create().

Hm, I don't understand. The (locking) intel_framebuffer_create
is used by intel_framebuffer_create_for_mode as well as
intel_user_framebuffer_create.

The (non-locking) __intel_framebuffer_create is used by
intelfb_alloc. So it seems both are needed. Daniel added
__intel_framebuffer_create with a8bb6818270c ("drm/i915:
Fix error path leak in fbdev fb allocation"). Incidentally
this is also the commit that introduced the double unref. :-)

We could eliminate the (non-locking) __intel_framebuffer_create
however by briefly unlocking struct_mutex in intelfb_alloc after
i915_gem_alloc_object and then relocking before
intel_pin_and_fence_fb_obj (this is on top of Tvrtko's patch
which moves the locking from intelfb_create to intelfb_alloc).

Best regards,

Lukas
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Re: [PATCH v3 2/2] drm/i915: On fb alloc failure, unref gem object where it gets refed

[Chris Wilson]

On Sun, Jul 05, 2015 at 06:49:02PM +0200, Lukas Wunner wrote:
> Hi Chris,
> 
> thank you for the quick response (on a weekend no less).
> 
> 
> On Sat, Jul 04, 2015 at 01:31:48PM +0100, Chris Wilson wrote:
> > > -	return intel_framebuffer_create(dev, &mode_cmd, obj);
> > > +	fb = intel_framebuffer_create(dev, &mode_cmd, obj);
> > > +	if (IS_ERR(fb))
> > > +		drm_gem_object_unreference(&obj->base);
> > 
> > This needs to be drm_gem_object_unreference_unlocked().
> 
> You're absolutely right, thanks for pointing this out.
> I'm posting a rectified v4 right now.
> 
> 
> > It's much simpler if you just document this as consuming the
> > obj reference.
> 
> Yes but I believe that is what Ville took exception to.
> 
> If you guys all agree that documenting this is sufficient then
> you can just merge Tvrtko's v2. The rationale of the v3 + v4
> I've submitted is to offer an alternative in the hope of pushing
> this forward.
> 
> 
> > If you want to fix it, you have to move the struct_mutex into
> > the caller i.e. eliminate intel_framebuffer_create() and call
> > __intel_framebuffer_create().
> 
> Hm, I don't understand. The (locking) intel_framebuffer_create
> is used by intel_framebuffer_create_for_mode as well as
> intel_user_framebuffer_create.
> 
> The (non-locking) __intel_framebuffer_create is used by
> intelfb_alloc. So it seems both are needed. Daniel added
> __intel_framebuffer_create with a8bb6818270c ("drm/i915:
> Fix error path leak in fbdev fb allocation"). Incidentally
> this is also the commit that introduced the double unref. :-)
> 
> We could eliminate the (non-locking) __intel_framebuffer_create
> however by briefly unlocking struct_mutex in intelfb_alloc after
> i915_gem_alloc_object and then relocking before
> intel_pin_and_fence_fb_obj (this is on top of Tvrtko's patch
> which moves the locking from intelfb_create to intelfb_alloc).

I mean, there will only be the non-locking variant, the mutex is moved
to the caller.
-Chris

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Re: [PATCH v4 2/2] drm/i915: On fb alloc failure, unref gem object where it gets refed

[Daniel Vetter]

On Sat, Jul 04, 2015 at 11:50:58AM +0200, Lukas Wunner wrote:
> Currently when allocating a framebuffer fails, the gem object gets
> unrefed at the bottom of the call chain in __intel_framebuffer_create,
> not where it gets refed, which is in intel_framebuffer_create_for_mode
> (via i915_gem_alloc_object) and in intel_user_framebuffer_create
> (via drm_gem_object_lookup).
> 
> This invites mistakes: As discovered by Tvrtko Ursulin, a double unref
> has sneaked into intelfb_alloc (which calls __intel_framebuffer_create).
> 
> As suggested by Ville Syrjälä, improve code clarity by moving the unref
> away from __intel_framebuffer_create to where the gem object gets refed.
> 
> Signed-off-by: Lukas Wunner <lukas@wunner.de>
> Fixes: a8bb6818270c ("drm/i915: Fix error path leak in fbdev fb
>     allocation")
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>

Please keep a record of the changes you do to the patch so I know what to
look out for. Just reving the patch revision alone doesn't add much
information for reviewers/maintainers.

Thanks, Daniel

> ---
>  drivers/gpu/drm/i915/intel_display.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 9079fcd..d597afa 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -8876,20 +8876,17 @@ __intel_framebuffer_create(struct drm_device *dev,
>  	int ret;
>  
>  	intel_fb = kzalloc(sizeof(*intel_fb), GFP_KERNEL);
> -	if (!intel_fb) {
> -		drm_gem_object_unreference(&obj->base);
> +	if (!intel_fb)
>  		return ERR_PTR(-ENOMEM);
> -	}
>  
>  	ret = intel_framebuffer_init(dev, intel_fb, mode_cmd, obj);
>  	if (ret)
>  		goto err;
>  
>  	return &intel_fb->base;
> +
>  err:
> -	drm_gem_object_unreference(&obj->base);
>  	kfree(intel_fb);
> -
>  	return ERR_PTR(ret);
>  }
>  
> @@ -8929,6 +8926,7 @@ intel_framebuffer_create_for_mode(struct drm_device *dev,
>  				  struct drm_display_mode *mode,
>  				  int depth, int bpp)
>  {
> +	struct drm_framebuffer *fb;
>  	struct drm_i915_gem_object *obj;
>  	struct drm_mode_fb_cmd2 mode_cmd = { 0 };
>  
> @@ -8943,7 +8941,11 @@ intel_framebuffer_create_for_mode(struct drm_device *dev,
>  								bpp);
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(bpp, depth);
>  
> -	return intel_framebuffer_create(dev, &mode_cmd, obj);
> +	fb = intel_framebuffer_create(dev, &mode_cmd, obj);
> +	if (IS_ERR(fb))
> +		drm_gem_object_unreference_unlocked(&obj->base);
> +
> +	return fb;
>  }
>  
>  static struct drm_framebuffer *
> @@ -13379,6 +13381,7 @@ intel_user_framebuffer_create(struct drm_device *dev,
>  			      struct drm_file *filp,
>  			      struct drm_mode_fb_cmd2 *mode_cmd)
>  {
> +	struct drm_framebuffer *fb;
>  	struct drm_i915_gem_object *obj;
>  
>  	obj = to_intel_bo(drm_gem_object_lookup(dev, filp,
> @@ -13386,7 +13389,11 @@ intel_user_framebuffer_create(struct drm_device *dev,
>  	if (&obj->base == NULL)
>  		return ERR_PTR(-ENOENT);
>  
> -	return intel_framebuffer_create(dev, mode_cmd, obj);
> +	fb = intel_framebuffer_create(dev, mode_cmd, obj);
> +	if (IS_ERR(fb))
> +		drm_gem_object_unreference_unlocked(&obj->base);
> +
> +	return fb;
>  }
>  
>  static void intel_output_poll_changed(struct drm_device *dev)
> -- 
> 2.1.0
> 

-- 
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Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH v4 2/2] drm/i915: On fb alloc failure, unref gem object where it gets refed

[Lukas Wunner]

Hi Daniel,

On Mon, Jul 06, 2015 at 09:41:51AM +0200, Daniel Vetter wrote:
> Please keep a record of the changes you do to the patch so I know what to
> look out for. Just reving the patch revision alone doesn't add much
> information for reviewers/maintainers.

There's a changelog in the first patch of this 2 patch series
(subject "[PATCH v4 1/2] drm/i915: Fix failure paths around
initial fbdev allocation"), it says:

"v4:
    * Lock struct mutex on unref. (Chris Wilson)"

Best regards,

Lukas
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Re: [PATCH v4 2/2] drm/i915: On fb alloc failure, unref gem object where it gets refed

[Daniel Vetter]

On Mon, Jul 06, 2015 at 02:59:02PM +0200, Lukas Wunner wrote:
> Hi Daniel,
> 
> On Mon, Jul 06, 2015 at 09:41:51AM +0200, Daniel Vetter wrote:
> > Please keep a record of the changes you do to the patch so I know what to
> > look out for. Just reving the patch revision alone doesn't add much
> > information for reviewers/maintainers.
> 
> There's a changelog in the first patch of this 2 patch series
> (subject "[PATCH v4 1/2] drm/i915: Fix failure paths around
> initial fbdev allocation"), it says:
> 
> "v4:
>     * Lock struct mutex on unref. (Chris Wilson)"

Ah, I was looking for the v4 changelog for patch 2. Either make a small
v4: rebased note or just don't call patch 2 v4 to avoid confusion in the
future.
-Daniel
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Lukas Wunner]

Hi Tvrtko,

On Mon, Jun 29, 2015 at 04:15:08PM +0100, Tvrtko Ursulin wrote:
> On 06/29/2015 03:39 PM, Lukas Wunner wrote:
> >On Mon, Jun 15, 2015 at 11:49:52AM +0100, Tvrtko Ursulin wrote:
> >>From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >>
> >>We had two failure modes here:
> >>
> >>1.
> >>Deadlock in intelfb_alloc failure path where it calls drm_framebuffer_remove,
> >>which grabs the struct mutex and intelfb_create (caller of intelfb_alloc) was
> >>already holding it.
> >
> >s/intelfb_alloc/intelfb_create/
> >s/(caller of intelfb_alloc)//
> 
> I looked again and don't see that I made a mistake with regards to this?

Sorry, I was confused myself:

Apart from the two issues you mentioned in the commit message there's
a third one fixed by this patch which could briefly be described as:

"Deadlock in intelfb_create failure path where it calls
drm_framebuffer_unreference, which grabs the struct mutex
and intelfb_create was already holding it."

Only that single issue was reported by me, the others were subsequently
discovered by you or your colleagues.

A somewhat more elaborate description is in my original report:
http://lists.freedesktop.org/archives/intel-gfx/2015-June/067965.html


> >I will also test the patch and report back in a bit.
> 
> That will be very useful. I did not test it extensively myself, just fired
> it off quickly since I was briefly hitting this failure path myself.

Okay the patch works for me (in the specific scenario on the
MacBook Pro where the existing fb is discarded because it is
too small and a new one is allocated).

PRTS did report some issue on Baytrail though:
http://lists.freedesktop.org/archives/intel-gfx/2015-June/069978.html

One nitpick is that your commit message exceeds 72 characters per line.

Also, Ville had posted a suggestion which was not discussed further,
removing the drm_gem_object_unreference() from __intel_framebuffer_create()
in favor of the one you now removed from intelfb_alloc(). (Personally
I'm totally indifferent on that.)

Best regards,

Lukas
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Tvrtko Ursulin]

Hi,

On 06/29/2015 03:39 PM, Lukas Wunner wrote:
> Hi,
>
> On Mon, Jun 15, 2015 at 11:49:52AM +0100, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> We had two failure modes here:
>>
>> 1.
>> Deadlock in intelfb_alloc failure path where it calls drm_framebuffer_remove,
>> which grabs the struct mutex and intelfb_create (caller of intelfb_alloc) was
>> already holding it.
>
> s/intelfb_alloc/intelfb_create/
> s/(caller of intelfb_alloc)//

I looked again and don't see that I made a mistake with regards to this?

>> 2.
>> Double unreference on the object if __intel_framebuffer_create fails since
>> both it and the caller (intelfb_alloc) do the unreference.
>>
>> 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>
>
> Fixes: 60a5ca015ffd2aacfe5674b5a401cd2a37159e07
> Reported-By: Lukas Wunner <lukas@wunner.de>

Sorry probably my oversight, don't remember now how it all came about.

>> @@ -183,15 +186,18 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>>   		goto out_fb;
>>   	}
>>
>> +	mutex_unlock(&dev->struct_mutex);
>> +
>>   	ifbdev->fb = to_intel_framebuffer(fb);
>>
>>   	return 0;
>>
>>   out_fb:
>> -	drm_framebuffer_remove(fb);
>> -out_unref:
>>   	drm_gem_object_unreference(&obj->base);
>>   out:
>> +	mutex_unlock(&dev->struct_mutex);
>> +	if (fb)
>> +		drm_framebuffer_remove(fb);
>
> Hm, the order of drm_gem_object_unreference() and drm_framebuffer_remove()
> is reversed now, could this cause any issues?

No, that is fine.

> Apart from that,
>
> Reviewed-By: Lukas Wunner <lukas@wunner.de>
>
> I will also test the patch and report back in a bit.

That will be very useful. I did not test it extensively myself, just 
fired it off quickly since I was briefly hitting this failure path myself.

Regards,

Tvrtko
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Lukas Wunner]

Hi,

On Mon, Jun 15, 2015 at 11:49:52AM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> We had two failure modes here:
> 
> 1.
> Deadlock in intelfb_alloc failure path where it calls drm_framebuffer_remove,
> which grabs the struct mutex and intelfb_create (caller of intelfb_alloc) was
> already holding it.

s/intelfb_alloc/intelfb_create/
s/(caller of intelfb_alloc)//


> 
> 2.
> Double unreference on the object if __intel_framebuffer_create fails since
> both it and the caller (intelfb_alloc) do the unreference.
> 
> 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>

Fixes: 60a5ca015ffd2aacfe5674b5a401cd2a37159e07
Reported-By: Lukas Wunner <lukas@wunner.de>


> ---
>  drivers/gpu/drm/i915/intel_fbdev.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 6372cfc..b998f69 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -141,7 +141,7 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  {
>  	struct intel_fbdev *ifbdev =
>  		container_of(helper, struct intel_fbdev, helper);
> -	struct drm_framebuffer *fb;
> +	struct drm_framebuffer *fb = NULL;
>  	struct drm_device *dev = helper->dev;
>  	struct drm_mode_fb_cmd2 mode_cmd = {};
>  	struct drm_i915_gem_object *obj;
> @@ -159,6 +159,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
>  							  sizes->surface_depth);
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	size = mode_cmd.pitches[0] * mode_cmd.height;
>  	size = PAGE_ALIGN(size);
>  	obj = i915_gem_object_create_stolen(dev, size);
> @@ -172,8 +174,9 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  
>  	fb = __intel_framebuffer_create(dev, &mode_cmd, obj);
>  	if (IS_ERR(fb)) {
> +		/* Drops object reference on failure. */
>  		ret = PTR_ERR(fb);
> -		goto out_unref;
> +		goto out;
>  	}
>  
>  	/* Flush everything out, we'll be doing GTT only from now on */
> @@ -183,15 +186,18 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  		goto out_fb;
>  	}
>  
> +	mutex_unlock(&dev->struct_mutex);
> +
>  	ifbdev->fb = to_intel_framebuffer(fb);
>  
>  	return 0;
>  
>  out_fb:
> -	drm_framebuffer_remove(fb);
> -out_unref:
>  	drm_gem_object_unreference(&obj->base);
>  out:
> +	mutex_unlock(&dev->struct_mutex);
> +	if (fb)
> +		drm_framebuffer_remove(fb);

Hm, the order of drm_gem_object_unreference() and drm_framebuffer_remove()
is reversed now, could this cause any issues?

Apart from that,

Reviewed-By: Lukas Wunner <lukas@wunner.de>

I will also test the patch and report back in a bit.

Thanks a lot,

Lukas


>  	return ret;
>  }
>  
> @@ -209,8 +215,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	int size, ret;
>  	bool prealloc = false;
>  
> -	mutex_lock(&dev->struct_mutex);
> -
>  	if (intel_fb &&
>  	    (sizes->fb_width > intel_fb->base.width ||
>  	     sizes->fb_height > intel_fb->base.height)) {
> @@ -225,7 +229,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  		DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
>  		ret = intelfb_alloc(helper, sizes);
>  		if (ret)
> -			goto out_unlock;
> +			return ret;
>  		intel_fb = ifbdev->fb;
>  	} else {
>  		DRM_DEBUG_KMS("re-using BIOS fb\n");
> @@ -237,6 +241,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	obj = intel_fb->obj;
>  	size = obj->base.size;
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	info = framebuffer_alloc(0, &dev->pdev->dev);
>  	if (!info) {
>  		ret = -ENOMEM;
> @@ -307,7 +313,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  out_unpin:
>  	i915_gem_object_ggtt_unpin(obj);
>  	drm_gem_object_unreference(&obj->base);
> -out_unlock:
>  	mutex_unlock(&dev->struct_mutex);
>  	return ret;
>  }
> -- 
> 2.4.2
> 
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[shuang.he]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he@intel.com)
Task id: 6642
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
ILK                                  302/302              302/302
SNB                                  312/316              312/316
IVB                                  343/343              343/343
BYT                 -1              287/287              286/287
HSW                                  380/380              380/380
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*BYT  igt@gem_tiled_partial_pwrite_pread@reads      PASS(1)      FAIL(1)
Note: You need to pay more attention to line start with '*'
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Re: [PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Ville Syrjälä]

On Mon, Jun 15, 2015 at 11:49:52AM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> We had two failure modes here:
> 
> 1.
> Deadlock in intelfb_alloc failure path where it calls drm_framebuffer_remove,
> which grabs the struct mutex and intelfb_create (caller of intelfb_alloc) was
> already holding it.
> 
> 2.
> Double unreference on the object if __intel_framebuffer_create fails since
> both it and the caller (intelfb_alloc) do the unreference.

I would suggest removing the unref from __intel_framebuffer_create().

> 
> 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>
> ---
>  drivers/gpu/drm/i915/intel_fbdev.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
> index 6372cfc..b998f69 100644
> --- a/drivers/gpu/drm/i915/intel_fbdev.c
> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> @@ -141,7 +141,7 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  {
>  	struct intel_fbdev *ifbdev =
>  		container_of(helper, struct intel_fbdev, helper);
> -	struct drm_framebuffer *fb;
> +	struct drm_framebuffer *fb = NULL;
>  	struct drm_device *dev = helper->dev;
>  	struct drm_mode_fb_cmd2 mode_cmd = {};
>  	struct drm_i915_gem_object *obj;
> @@ -159,6 +159,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
>  							  sizes->surface_depth);
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	size = mode_cmd.pitches[0] * mode_cmd.height;
>  	size = PAGE_ALIGN(size);
>  	obj = i915_gem_object_create_stolen(dev, size);
> @@ -172,8 +174,9 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  
>  	fb = __intel_framebuffer_create(dev, &mode_cmd, obj);
>  	if (IS_ERR(fb)) {
> +		/* Drops object reference on failure. */
>  		ret = PTR_ERR(fb);
> -		goto out_unref;
> +		goto out;
>  	}
>  
>  	/* Flush everything out, we'll be doing GTT only from now on */
> @@ -183,15 +186,18 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
>  		goto out_fb;
>  	}
>  
> +	mutex_unlock(&dev->struct_mutex);
> +
>  	ifbdev->fb = to_intel_framebuffer(fb);
>  
>  	return 0;
>  
>  out_fb:
> -	drm_framebuffer_remove(fb);
> -out_unref:
>  	drm_gem_object_unreference(&obj->base);
>  out:
> +	mutex_unlock(&dev->struct_mutex);
> +	if (fb)
> +		drm_framebuffer_remove(fb);
>  	return ret;
>  }
>  
> @@ -209,8 +215,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	int size, ret;
>  	bool prealloc = false;
>  
> -	mutex_lock(&dev->struct_mutex);
> -
>  	if (intel_fb &&
>  	    (sizes->fb_width > intel_fb->base.width ||
>  	     sizes->fb_height > intel_fb->base.height)) {
> @@ -225,7 +229,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  		DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
>  		ret = intelfb_alloc(helper, sizes);
>  		if (ret)
> -			goto out_unlock;
> +			return ret;
>  		intel_fb = ifbdev->fb;
>  	} else {
>  		DRM_DEBUG_KMS("re-using BIOS fb\n");
> @@ -237,6 +241,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  	obj = intel_fb->obj;
>  	size = obj->base.size;
>  
> +	mutex_lock(&dev->struct_mutex);
> +
>  	info = framebuffer_alloc(0, &dev->pdev->dev);
>  	if (!info) {
>  		ret = -ENOMEM;
> @@ -307,7 +313,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
>  out_unpin:
>  	i915_gem_object_ggtt_unpin(obj);
>  	drm_gem_object_unreference(&obj->base);
> -out_unlock:
>  	mutex_unlock(&dev->struct_mutex);
>  	return ret;
>  }
> -- 
> 2.4.2

-- 
Ville Syrjälä
Intel OTC
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[PATCH] drm/i915: Fix failure paths around initial fbdev allocation

[Tvrtko Ursulin]

From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

We had two failure modes here:

1.
Deadlock in intelfb_alloc failure path where it calls drm_framebuffer_remove,
which grabs the struct mutex and intelfb_create (caller of intelfb_alloc) was
already holding it.

2.
Double unreference on the object if __intel_framebuffer_create fails since
both it and the caller (intelfb_alloc) do the unreference.

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>
---
 drivers/gpu/drm/i915/intel_fbdev.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index 6372cfc..b998f69 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -141,7 +141,7 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 {
 	struct intel_fbdev *ifbdev =
 		container_of(helper, struct intel_fbdev, helper);
-	struct drm_framebuffer *fb;
+	struct drm_framebuffer *fb = NULL;
 	struct drm_device *dev = helper->dev;
 	struct drm_mode_fb_cmd2 mode_cmd = {};
 	struct drm_i915_gem_object *obj;
@@ -159,6 +159,8 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 	mode_cmd.pixel_format = drm_mode_legacy_fb_format(sizes->surface_bpp,
 							  sizes->surface_depth);
 
+	mutex_lock(&dev->struct_mutex);
+
 	size = mode_cmd.pitches[0] * mode_cmd.height;
 	size = PAGE_ALIGN(size);
 	obj = i915_gem_object_create_stolen(dev, size);
@@ -172,8 +174,9 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 
 	fb = __intel_framebuffer_create(dev, &mode_cmd, obj);
 	if (IS_ERR(fb)) {
+		/* Drops object reference on failure. */
 		ret = PTR_ERR(fb);
-		goto out_unref;
+		goto out;
 	}
 
 	/* Flush everything out, we'll be doing GTT only from now on */
@@ -183,15 +186,18 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
 		goto out_fb;
 	}
 
+	mutex_unlock(&dev->struct_mutex);
+
 	ifbdev->fb = to_intel_framebuffer(fb);
 
 	return 0;
 
 out_fb:
-	drm_framebuffer_remove(fb);
-out_unref:
 	drm_gem_object_unreference(&obj->base);
 out:
+	mutex_unlock(&dev->struct_mutex);
+	if (fb)
+		drm_framebuffer_remove(fb);
 	return ret;
 }
 
@@ -209,8 +215,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
 	int size, ret;
 	bool prealloc = false;
 
-	mutex_lock(&dev->struct_mutex);
-
 	if (intel_fb &&
 	    (sizes->fb_width > intel_fb->base.width ||
 	     sizes->fb_height > intel_fb->base.height)) {
@@ -225,7 +229,7 @@ static int intelfb_create(struct drm_fb_helper *helper,
 		DRM_DEBUG_KMS("no BIOS fb, allocating a new one\n");
 		ret = intelfb_alloc(helper, sizes);
 		if (ret)
-			goto out_unlock;
+			return ret;
 		intel_fb = ifbdev->fb;
 	} else {
 		DRM_DEBUG_KMS("re-using BIOS fb\n");
@@ -237,6 +241,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
 	obj = intel_fb->obj;
 	size = obj->base.size;
 
+	mutex_lock(&dev->struct_mutex);
+
 	info = framebuffer_alloc(0, &dev->pdev->dev);
 	if (!info) {
 		ret = -ENOMEM;
@@ -307,7 +313,6 @@ static int intelfb_create(struct drm_fb_helper *helper,
 out_unpin:
 	i915_gem_object_ggtt_unpin(obj);
 	drm_gem_object_unreference(&obj->base);
-out_unlock:
 	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
-- 
2.4.2

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