[PATCH 1/2][Lucid SRU] drm/i915: Hold a reference to the object whilst unbinding the eviction list

[Seth Forshee]

From: Chris Wilson <chris at chris-wilson.co.uk>

BugLink: http://bugs.launchpad.net/bugs/843904

During heavy aperture thrashing we may be forced to wait upon several active
objects during eviction. The active list may be the last reference to
these objects and so the action of waiting upon one of them may cause
another to be freed (and itself unbound). To prevent the object
disappearing underneath us, we need to acquire and hold a reference
whilst unbinding.

This should fix the reported page refcount OOPS:

kernel BUG at drivers/gpu/drm/i915/i915_gem.c:1444!
...
RIP: 0010:[<ffffffffa0093026>]  [<ffffffffa0093026>] i915_gem_object_put_pages+0x25/0xf5 [i915]
Call Trace:
 [<ffffffffa009481d>] i915_gem_object_unbind+0xc5/0x1a7 [i915]
 [<ffffffffa0098ab2>] i915_gem_evict_something+0x3bd/0x409 [i915]
 [<ffffffffa0027923>] ? drm_gem_object_lookup+0x27/0x57 [drm]
 [<ffffffffa0093bc3>] i915_gem_object_bind_to_gtt+0x1d3/0x279 [i915]
 [<ffffffffa0095b30>] i915_gem_object_pin+0xa3/0x146 [i915]
 [<ffffffffa0027948>] ? drm_gem_object_lookup+0x4c/0x57 [drm]
 [<ffffffffa00961bc>] i915_gem_do_execbuffer+0x50d/0xe32 [i915]

Reported-by: Shawn Starr <shawn.starr at rogers.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=18902
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
(backported from commit af6261031317f646d22f994c0b467521e47aa49f upstream)

Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
---
 drivers/gpu/drm/i915/i915_gem_evict.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_evict.c b/drivers/gpu/drm/i915/i915_gem_evict.c
index c4c6b6f..c50c093 100644
--- a/drivers/gpu/drm/i915/i915_gem_evict.c
+++ b/drivers/gpu/drm/i915/i915_gem_evict.c
@@ -52,6 +52,7 @@ mark_free(struct drm_i915_gem_object *obj_priv,
 	   struct list_head *unwind)
 {
 	list_add(&obj_priv->evict_list, unwind);
+	drm_gem_object_reference(obj_priv->obj);
 	return drm_mm_scan_add_block(obj_priv->gtt_space);
 }
 
@@ -143,6 +144,7 @@ i915_gem_evict_something(struct drm_device *dev, int min_size, unsigned alignmen
 		BUG_ON(ret);
 
 		list_del_init(&obj_priv->evict_list);
+		drm_gem_object_unreference(obj_priv->obj);
 	}
 
 	/* We expect the caller to unpin, evict all and try again, or give up.
@@ -162,6 +164,7 @@ found:
 			continue;
 		}
 		list_del_init(&obj_priv->evict_list);
+		drm_gem_object_unreference(obj_priv->obj);
 	}
 
 	/* Unbinding will emit any required flushes */
@@ -173,6 +176,7 @@ found:
 			ret = i915_gem_object_unbind(obj_priv->obj);
 
 		list_del_init(&obj_priv->evict_list);
+		drm_gem_object_unreference(obj_priv->obj);
 	}
 
 	return 0;
-- 
1.7.4.1