The conditional is usually a recoverable driver bug, and so WARNing, and preventing the drm_mm code from doing potential damage (BUG) is desirable.

This issue was hit and fixed twice while developing the i915 multiple address space code. The first fix is the patch just before this, and is hit on an not frequently occuring error path. Another was fixed during patch iteration, so it's hard to see from the patch:

commit c6cfb325677ea6305fb19acf3a4d14ea267f923e Author: Ben Widawsky ben@bwidawsk.net Date: Fri Jul 5 14:41:06 2013 -0700

drm/i915: Embed drm_mm_node in i915 gem obj

From the intel-gfx mailing list, we discussed this:

References: 20130705191235.GA3057@bwidawsk.net

Cc: Dave Airlie airlied@redhat.com CC: dri-devel@lists.freedesktop.org Signed-off-by: Ben Widawsky ben@bwidawsk.net --- drivers/gpu/drm/drm_mm.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c index aded1e1..af93cc5 100644 --- a/drivers/gpu/drm/drm_mm.c +++ b/drivers/gpu/drm/drm_mm.c @@ -254,6 +254,9 @@ void drm_mm_remove_node(struct drm_mm_node *node) struct drm_mm *mm = node->mm; struct drm_mm_node *prev_node;

+ if (WARN_ON(!node->allocated)) + return; + BUG_ON(node->scanned_block || node->scanned_prev_free || node->scanned_next_free);