[PATCH v2] drm/amdgpu: fix root reservation in amdgpu_vm_handle_fault

[Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>]

svm_range_restore_pages might reserve the root bo so it must
be called after unreserving it.

---
v2:
  - don't modify amdgpu_vm_lock_by_pasid
  - add a TODO
---

Fixes: 32b486e8541c ("drm/amdgpu: extract amdgpu_vm_lock_by_pasid from amdgpu_vm_handle_fault")
Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index 63156289ae7f..799a1803d941 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -3026,11 +3026,22 @@ bool amdgpu_vm_handle_fault(struct amdgpu_device *adev, u32 pasid,
 
 	is_compute_context = vm->is_compute_context;
 
-	if (is_compute_context && !svm_range_restore_pages(adev, pasid, vmid,
-	    node_id, addr >> PAGE_SHIFT, ts, write_fault)) {
+	if (is_compute_context) {
+		/* Unreserve root since svm_range_restore_pages might try to reserve it. */
+		/* TODO: rework svm_range_restore_pages so that this isn't necessary. */
 		amdgpu_bo_unreserve(root);
+
+		if (!svm_range_restore_pages(adev, pasid, vmid,
+					     node_id, addr >> PAGE_SHIFT, ts, write_fault)) {
+			amdgpu_bo_unref(&root);
+			return true;
+		}
 		amdgpu_bo_unref(&root);
-		return true;
+
+		/* Double check that the VM still exists. */
+		vm = amdgpu_vm_lock_by_pasid(adev, &root, pasid);
+		if (!vm)
+			return false;
 	}
 
 	addr /= AMDGPU_GPU_PAGE_SIZE;
-- 
2.43.0