1 files changed, 22 insertions, 8 deletions

diff --git a/drivers/infiniband/hw/mlx5/odp.c b/drivers/infiniband/hw/mlx5/odp.c
index f655859eec00..f1e23583e6c0 100644
--- a/drivers/infiniband/hw/mlx5/odp.c
+++ b/drivers/infiniband/hw/mlx5/odp.c
@@ -228,13 +228,27 @@ static void destroy_unused_implicit_child_mr(struct mlx5_ib_mr *mr)
 	unsigned long idx = ib_umem_start(odp) >> MLX5_IMR_MTT_SHIFT;
 	struct mlx5_ib_mr *imr = mr->parent;
 
+	/*
+	 * If userspace is racing freeing the parent implicit ODP MR then we can
+	 * loose the race with parent destruction. In this case
+	 * mlx5_ib_free_odp_mr() will free everything in the implicit_children
+	 * xarray so NOP is fine. This child MR cannot be destroyed here because
+	 * we are under its umem_mutex.
+	 */
 	if (!refcount_inc_not_zero(&imr->mmkey.usecount))
 		return;
 
-	xa_erase(&imr->implicit_children, idx);
+	xa_lock(&imr->implicit_children);
+	if (__xa_cmpxchg(&imr->implicit_children, idx, mr, NULL, GFP_KERNEL) !=
+	    mr) {
+		xa_unlock(&imr->implicit_children);
+		return;
+	}
+
 	if (MLX5_CAP_ODP(mr_to_mdev(mr)->mdev, mem_page_fault))
-		xa_erase(&mr_to_mdev(mr)->odp_mkeys,
-			 mlx5_base_mkey(mr->mmkey.key));
+		__xa_erase(&mr_to_mdev(mr)->odp_mkeys,
+			   mlx5_base_mkey(mr->mmkey.key));
+	xa_unlock(&imr->implicit_children);
 
 	/* Freeing a MR is a sleeping operation, so bounce to a work queue */
 	INIT_WORK(&mr->odp_destroy.work, free_implicit_child_mr_work);
@@ -502,18 +516,18 @@ static struct mlx5_ib_mr *implicit_get_child_mr(struct mlx5_ib_mr *imr,
 		refcount_inc(&ret->mmkey.usecount);
 		goto out_lock;
 	}
-	xa_unlock(&imr->implicit_children);
 
 	if (MLX5_CAP_ODP(dev->mdev, mem_page_fault)) {
-		ret = xa_store(&dev->odp_mkeys, mlx5_base_mkey(mr->mmkey.key),
-			       &mr->mmkey, GFP_KERNEL);
+		ret = __xa_store(&dev->odp_mkeys, mlx5_base_mkey(mr->mmkey.key),
+				 &mr->mmkey, GFP_KERNEL);
 		if (xa_is_err(ret)) {
 			ret = ERR_PTR(xa_err(ret));
-			xa_erase(&imr->implicit_children, idx);
-			goto out_mr;
+			__xa_erase(&imr->implicit_children, idx);
+			goto out_lock;
 		}
 		mr->mmkey.type = MLX5_MKEY_IMPLICIT_CHILD;
 	}
+	xa_unlock(&imr->implicit_children);
 	mlx5_ib_dbg(mr_to_mdev(imr), "key %x mr %p\n", mr->mmkey.key, mr);
 	return mr;