[PATCH 5.7 144/166] drm/i915: Drop vm.ref for duplicate vma on construction

[Greg Kroah-Hartman]

From: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>

commit 42723673a193d5f8e30dba6ea9826d42262a502b upstream.

As we allow for parallel threads to create the same vma instance
concurrently, and we only filter out the duplicates upon reacquiring the
spinlock for the rbtree, we have to free the loser of the constructors'
race. When freeing, we should also drop any resource references acquired
for the redundant vma.

Fixes: 2850748ef876 ("drm/i915: Pull i915_vma_pin under the vm->mutex")
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.5+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20200702083225.20044-1-chris@xxxxxxxxxxxxxxxxxx
(cherry picked from commit 2377427cdd2b7514eb4c40241cf5c4dec63c1bec)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/i915_vma.c |    1 +
 1 file changed, 1 insertion(+)

--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -198,6 +198,7 @@ vma_create(struct drm_i915_gem_object *o
 		cmp = i915_vma_compare(pos, vm, view);
 		if (cmp == 0) {
 			spin_unlock(&obj->vma.lock);
+			i915_vm_put(vm);
 			i915_vma_free(vma);
 			return pos;
 		}