[Intel-gfx] [PATCH] [v2] drm/i915/vma: Correct use after free in eviction

[Ben Widawsky]

The vma will [possibly] be destroyed during unbind in eviction.
Immediately after this, we try to delete the list entry.

Chris and Ville did the debug on this before I woke up, I just get to
take credit for the fix :p

v2: Missed the drm_object_unreference use after free (Ville)

Reported-by: Mika Kuoppala <mika.kuoppala at intel.com>
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem_evict.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
index 0cbaad4..3b7b74e 100644
--- a/drivers/gpu/drm/i915/i915_gem_evict.c
+++ b/drivers/gpu/drm/i915/i915_gem_evict.c
@@ -136,14 +136,17 @@ found:
 
 	/* Unbinding will emit any required flushes */
 	while (!list_empty(&eviction_list)) {
+		struct drm_gem_object *obj;
 		vma = list_first_entry(&eviction_list,
 				       struct i915_vma,
 				       exec_list);
+
+		obj =  &vma->obj->base;
+		list_del_init(&vma->exec_list);
 		if (ret == 0)
 			ret = i915_vma_unbind(vma);
 
-		list_del_init(&vma->exec_list);
-		drm_gem_object_unreference(&vma->obj->base);
+		drm_gem_object_unreference(obj);
 	}
 
 	return ret;
-- 
1.8.3.4