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

Lukas Wunner
2015-07-04T12:21:14Z

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