[PATCH v2 15/22 RESEND] 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.

[Changelog is in preceding patch by Tvrtko Ursulin.]

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=88861
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=61115
Tested-by: Paul Hordiienko <pvt.gord at gmail.com>
    [MBP  6,2 2010  intel ILK + nvidia GT216  pre-retina]
Tested-by: William Brown <william at blackhats.net.au>
    [MBP  8,2 2011  intel SNB + amd turks     pre-retina]
Tested-by: Lukas Wunner <lukas at wunner.de>
    [MBP  9,1 2012  intel IVB + nvidia GK107  pre-retina]
Tested-by: Bruno Bierbaumer <bruno at bierbaumer.net>
    [MBP 11,3 2013  intel HSW + nvidia GK107  retina -- work in progress]

Signed-off-by: Lukas Wunner <lukas at wunner.de>
Fixes: a8bb6818270c ("drm/i915: Fix error path leak in fbdev fb
    allocation")
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Ville Syrjälä <ville.syrjala at 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 907b73e..5984d5f 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -10145,20 +10145,17 @@ __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);
 }
 
@@ -10198,6 +10195,7 @@ 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 };
 
@@ -10212,7 +10210,11 @@ 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 *
@@ -14468,6 +14470,7 @@ 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,
@@ -14475,7 +14478,11 @@ 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)
-- 
1.8.5.2 (Apple Git-48)