[Intel-gfx] [PATCH] drm/i915: Don't destroy the vma placeholder during execbuffer reservation

[Chris Wilson]

The execbuffer handle and exec_link were moved from the object into the
vma. As the vma may be unbound and destroyed whilst attempting to
reserve the execbuffer objects (either through a forced unbind to fix up
a misalignment or through an evict-everything call) we need to prevent
the free of the i915_vma itself. Otherwise not only is the list of
objects to reserve corrupt, but we continue to reference stale vma
entries.

Fixes kernel crash with i-g-t/gem_evict_everything

Reported-by: Dan Carpenter <dan.carpenter at oracle.com>
Bugzilla; https://bugs.freedesktop.org/show_bug.cgi?id=68298
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index bf32b1e..33bbd69 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4256,6 +4256,11 @@ void i915_gem_vma_destroy(struct i915_vma *vma)
 {
 	WARN_ON(vma->node.allocated);
 	list_del(&vma->vma_link);
+
+	/* Keep the vma as a placeholder in the execbuffer reservation lists */
+	if (!list_empty(&vma->exec_list))
+		return;
+
 	kfree(vma);
 }
 
-- 
1.8.4.rc3