[PATCH 3/4] drm: WARN when removing unallocated node

[Ben Widawsky]

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 at 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 at bwidawsk.net>

Cc: Dave Airlie <airlied at redhat.com>
CC: <dri-devel at lists.freedesktop.org>
Acked-by: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben at 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);
 
-- 
1.8.3.4