[Intel-gfx] [PATCH 1/2] drm/i915: Take the object lock when destroying vmas from vm destruction

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

Currently we guarantee that vmas stay alive when the object lock is held
only if we also hold a private vm reference. In order to relax the latter
requirement, take the object lock also when destroying vmas from the
vm destruction path.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
---
 drivers/gpu/drm/i915/gt/intel_gtt.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.c b/drivers/gpu/drm/i915/gt/intel_gtt.c
index b67831833c9a..92e22f727f88 100644
--- a/drivers/gpu/drm/i915/gt/intel_gtt.c
+++ b/drivers/gpu/drm/i915/gt/intel_gtt.c
@@ -112,7 +112,10 @@ int map_pt_dma_locked(struct i915_address_space *vm, struct drm_i915_gem_object
 static void clear_vm_list(struct list_head *list)
 {
 	struct i915_vma *vma, *vn;
+	bool unlocked;
 
+restart:
+	unlocked = false;
 	list_for_each_entry_safe(vma, vn, list, vm_link) {
 		struct drm_i915_gem_object *obj = vma->obj;
 
@@ -138,8 +141,22 @@ static void clear_vm_list(struct list_head *list)
 			i915_vm_resv_get(vma->vm);
 			vma->vm_ddestroy = true;
 		} else {
+			if (!i915_gem_object_trylock(obj, NULL)) {
+				unlocked = true;
+				mutex_unlock(&vma->vm->mutex);
+				i915_gem_object_lock(obj, NULL);
+				mutex_lock(&vma->vm->mutex);
+				/*
+				 * The vma may now be on a different list,
+				 * but not destroyed. We don't care.
+				 * destroy it.
+				 */
+			}
 			i915_vma_destroy_locked(vma);
+			i915_gem_object_unlock(obj);
 			i915_gem_object_put(obj);
+			if (unlocked)
+				goto restart;
 		}
 
 	}
-- 
2.36.1