From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
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.
[Daniel Vetter on why struct_mutex needs to be locked in the second half
of intelfb_create: "The vma [for the fbdev] is pinned, the problem is
that we re-lookup it a few times, which is racy. We should instead track
the vma directly, but oh well we don't."]
v2:
* Reformat commit msg to 72 chars. (Lukas Wunner)
* Add third failure mode. (Lukas Wunner)
v5:
* Rebase on drm-intel-nightly 2015y-09m-01d-09h-06m-08s UTC,
rephrase commit message. (Jani Nicula)
v6:
* In intelfb_alloc, if __intel_framebuffer_create failed,
fb will be an ERR_PTR, thus not null. So in the failure
path we need to check for IS_ERR_OR_NULL to avoid calling
drm_framebuffer_remove on the ERR_PTR. (Lukas Wunner)
* Since this is init code a drm_framebuffer_unreference should
be all we need. drm_framebuffer_remove is for framebuffers
that userspace has created - and is getting somewhat
defeatured. (Daniel Vetter)
v7:
* Clarify why struct_mutex needs to be locked in the second half
of intelfb_create. (Daniel Vetter)
Fixes: 60a5ca015ffd ("drm/i915: Add locking around
framebuffer_references--")
Reported-by: Lukas Wunner <lukas@xxxxxxxxx>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
[Lukas: Create v3 + v4 + v5 + v6 + v7 based on Tvrtko's v2]
Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
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 2240e70..db82ad4 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -119,7 +119,7 @@ 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_i915_private *dev_priv = to_i915(dev);
struct drm_mode_fb_cmd2 mode_cmd = {};
@@ -138,6 +138,8 @@ 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);
@@ -165,16 +167,19 @@ static int intelfb_alloc(struct drm_fb_helper *helper,
ret = intel_pin_and_fence_fb_obj(NULL, fb, NULL);
if (ret) {
DRM_ERROR("failed to pin obj: %d\n", ret);
- goto out_fb;
+ goto out;
}
+ mutex_unlock(&dev->struct_mutex);
+
ifbdev->fb = to_intel_framebuffer(fb);
return 0;
-out_fb:
- drm_framebuffer_remove(fb);
out:
+ mutex_unlock(&dev->struct_mutex);
+ if (!IS_ERR_OR_NULL(fb))
+ drm_framebuffer_unreference(fb);
return ret;
}
@@ -192,8 +197,6 @@ 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)) {
@@ -208,7 +211,7 @@ 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");
@@ -220,6 +223,8 @@ static int intelfb_create(struct drm_fb_helper *helper,
obj = intel_fb->obj;
size = obj->base.size;
+ mutex_lock(&dev->struct_mutex);
+
info = drm_fb_helper_alloc_fbi(helper);
if (IS_ERR(info)) {
ret = PTR_ERR(info);
@@ -281,7 +286,6 @@ out_destroy_fbi:
out_unpin:
i915_gem_object_ggtt_unpin(obj);
drm_gem_object_unreference(&obj->base);
-out_unlock:
mutex_unlock(&dev->struct_mutex);
return ret;
}
--
1.8.5.2 (Apple Git-48)
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