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Commit 51f1385b authored by Tvrtko Ursulin's avatar Tvrtko Ursulin Committed by Jani Nikula
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drm/i915: Fix failure paths around initial fbdev allocation 



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: 60a5ca01 ("drm/i915: Add locking around
    framebuffer_references--")
Reported-by: default avatarLukas Wunner <lukas@wunner.de>
Signed-off-by: default avatarTvrtko Ursulin <tvrtko.ursulin@intel.com>
[Lukas: Create v3 + v4 + v5 + v6 + v7 based on Tvrtko's v2]
Signed-off-by: default avatarLukas Wunner <lukas@wunner.de>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/47d4e88c91b3bf0f7a280cabec54c8c8cf0cf6f2.1446892879.git.lukas@wunner.de


Signed-off-by: default avatarJani Nikula <jani.nikula@intel.com>
parent ca40ba85

drivers/gpu/drm/i915/intel_fbdev.c

+12 −8
Original line number Diff line number Diff line
@@ -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 @@ 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;

}