drm/i915: Don't BUG_ON in i915_gem_obj_offset

A WARN_ON is perfectly fine.

The BUG in here seems to be the cause behind hard-hangs when I cat the
i915_gem_pageflip debugfs file (which calls this from an irq
spinlock). But only while running a full igt run after a while. I
still need to root cause the underlying issue.

I'll also start reject patches which add new BUG_ON but don't come
with a really good justification for it. The general rule really
should be to just WARN and hope the driver survives for long enough.

v2: Make the WARN a bit more useful per Chris' suggestion.

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index d836413..d857f58 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -5078,12 +5078,13 @@ unsigned long i915_gem_obj_offset(struct drm_i915_gem_object *o,
            vm == &dev_priv->mm.aliasing_ppgtt->base)
                vm = &dev_priv->gtt.base;
 
-       BUG_ON(list_empty(&o->vma_list));
        list_for_each_entry(vma, &o->vma_list, vma_link) {
                if (vma->vm == vm)
                        return vma->node.start;
 
        }
+       WARN(1, "%s vma for this object not found.\n",
+            i915_is_ggtt(vm) ? "global" : "ppgtt");
        return -1;
 }