[Intel-gfx] [PATCH 2/3] drm/i915/vma: Mark vmas busy during execbuf lookup

[Ben Widawsky]

The exec_list is a somewhat fragile list containing all the VMAs we've
looked up. It does processing in a multi-stage approach where elements
on the list are expected to not be removed for the duration of the
stages.

The next patch will fix an oversight where destroying a VMA does not
remove it from the exec_list. As such, we must mark the VMA busy for the
multi stage execbuf or else the above assertion we mentioned cannot be
guaranteed.

NOTE: This patch isn't quite tested yet. It just fixes the theoretical
issue.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben at bwidawsk.net>
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 9b3b5f8..7d8c841 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -516,6 +516,8 @@ i915_gem_execbuffer_unreserve_vma(struct i915_vma *vma)
 		i915_gem_object_unpin(obj);
 
 	entry->flags &= ~(__EXEC_OBJECT_HAS_FENCE | __EXEC_OBJECT_HAS_PIN);
+
+	vma->busy = 0;
 }
 
 static int
@@ -535,6 +537,7 @@ i915_gem_execbuffer_reserve(struct intel_ring_buffer *ring,
 		bool need_fence, need_mappable;
 
 		vma = list_first_entry(vmas, struct i915_vma, exec_list);
+		vma->busy = true;
 		obj = vma->obj;
 		entry = vma->exec_entry;
 
-- 
1.8.3.4