Re: [PATCH rdma-next] RDMA/restrack: Delay QP deletion till all users are gone

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Apr 21, 2021 at 08:03:22AM +0300, Leon Romanovsky wrote:

> I didn't understand when reviewed either, but decided to post it anyway
> to get possible explanation for this RDMA_RESTRACK_MR || RDMA_RESTRACK_QP
> check.

I think the whole thing should look more like this and we delete the
if entirely.

diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
index 2b9ffc21cbc4ad..479b16b8f6723a 100644
--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -1860,6 +1860,7 @@ static void _destroy_id(struct rdma_id_private *id_priv,
 				iw_destroy_cm_id(id_priv->cm_id.iw);
 		}
 		cma_leave_mc_groups(id_priv);
+		rdma_restrack_del(&id_priv->res);
 		cma_release_dev(id_priv);
 	}
 
@@ -1873,7 +1874,6 @@ static void _destroy_id(struct rdma_id_private *id_priv,
 	kfree(id_priv->id.route.path_rec);
 
 	put_net(id_priv->id.route.addr.dev_addr.net);
-	rdma_restrack_del(&id_priv->res);
 	kfree(id_priv);
 }
 
diff --git a/drivers/infiniband/core/counters.c b/drivers/infiniband/core/counters.c
index 15493357cfef09..1808bc2533f155 100644
--- a/drivers/infiniband/core/counters.c
+++ b/drivers/infiniband/core/counters.c
@@ -176,6 +176,8 @@ static void rdma_counter_free(struct rdma_counter *counter)
 {
 	struct rdma_port_counter *port_counter;
 
+	rdma_restrack_del(&counter->res);
+
 	port_counter = &counter->device->port_data[counter->port].port_counter;
 	mutex_lock(&port_counter->lock);
 	port_counter->num_counters--;
@@ -185,7 +187,6 @@ static void rdma_counter_free(struct rdma_counter *counter)
 
 	mutex_unlock(&port_counter->lock);
 
-	rdma_restrack_del(&counter->res);
 	kfree(counter->stats);
 	kfree(counter);
 }
diff --git a/drivers/infiniband/core/cq.c b/drivers/infiniband/core/cq.c
index 433b426729d4ce..3884db637d33ab 100644
--- a/drivers/infiniband/core/cq.c
+++ b/drivers/infiniband/core/cq.c
@@ -339,11 +339,15 @@ void ib_free_cq(struct ib_cq *cq)
 		WARN_ON_ONCE(1);
 	}
 
+	rdma_restrack_prepare_del(&cq->res);
 	rdma_dim_destroy(cq);
 	trace_cq_free(cq);
 	ret = cq->device->ops.destroy_cq(cq, NULL);
-	WARN_ONCE(ret, "Destroy of kernel CQ shouldn't fail");
-	rdma_restrack_del(&cq->res);
+	if (WARN_ON(ret)) {
+		rdma_restrack_abort_del(&cq->res);
+		return;
+	}
+	rdma_restrack_finish_del(&cq->res);
 	kfree(cq->wc);
 	kfree(cq);
 }
diff --git a/drivers/infiniband/core/rdma_core.c b/drivers/infiniband/core/rdma_core.c
index 94d83b665a2fe0..f57234ced93ca1 100644
--- a/drivers/infiniband/core/rdma_core.c
+++ b/drivers/infiniband/core/rdma_core.c
@@ -854,6 +854,8 @@ static void ufile_destroy_ucontext(struct ib_uverbs_file *ufile,
 	struct ib_ucontext *ucontext = ufile->ucontext;
 	struct ib_device *ib_dev = ucontext->device;
 
+	rdma_restrack_prepare_del(&ucontext->res);
+
 	/*
 	 * If we are closing the FD then the user mmap VMAs must have
 	 * already been destroyed as they hold on to the filep, otherwise
@@ -868,9 +870,8 @@ static void ufile_destroy_ucontext(struct ib_uverbs_file *ufile,
 	ib_rdmacg_uncharge(&ucontext->cg_obj, ib_dev,
 			   RDMACG_RESOURCE_HCA_HANDLE);
 
-	rdma_restrack_del(&ucontext->res);
-
 	ib_dev->ops.dealloc_ucontext(ucontext);
+	rdma_restrack_finish_del(&ucontext->res);
 	WARN_ON(!xa_empty(&ucontext->mmap_xa));
 	kfree(ucontext);
 
diff --git a/drivers/infiniband/core/restrack.c b/drivers/infiniband/core/restrack.c
index 033207882c82ce..8aa1dae40f38a7 100644
--- a/drivers/infiniband/core/restrack.c
+++ b/drivers/infiniband/core/restrack.c
@@ -315,11 +315,49 @@ int rdma_restrack_put(struct rdma_restrack_entry *res)
 }
 EXPORT_SYMBOL(rdma_restrack_put);
 
-/**
- * rdma_restrack_del() - delete object from the reource tracking database
- * @res:  resource entry
- */
-void rdma_restrack_del(struct rdma_restrack_entry *res)
+void rdma_restrack_prepare_del(struct rdma_restrack_entry *res)
+{
+	struct rdma_restrack_entry *old;
+	struct rdma_restrack_root *rt;
+	struct ib_device *dev;
+
+	if (!res->valid)
+		return;
+
+	dev = res_to_dev(res);
+	rt = &dev->res[res->type];
+
+	if (!res->no_track) {
+		old = xa_cmpxchg(&rt->xa, res->id, res, XA_ZERO_ENTRY,
+				 GFP_KERNEL);
+		WARN_ON(old != res);
+	}
+
+	/* Fence access from all concurrent threads, like netlink */
+	rdma_restrack_put(res);
+	wait_for_completion(&res->comp);
+}
+EXPORT_SYMBOL(rdma_restrack_prepare_del);
+
+void rdma_restrack_abort_del(struct rdma_restrack_entry *res)
+{
+	struct rdma_restrack_entry *old;
+	struct rdma_restrack_root *rt;
+	struct ib_device *dev;
+
+	if (!res->valid || res->no_track)
+		return;
+
+	dev = res_to_dev(res);
+	rt = &dev->res[res->type];
+
+	kref_init(&res->kref);
+	old = xa_cmpxchg(&rt->xa, res->id, XA_ZERO_ENTRY, res, GFP_KERNEL);
+	WARN_ON(old != res);
+}
+EXPORT_SYMBOL(rdma_restrack_abort_del);
+
+void rdma_restrack_finish_del(struct rdma_restrack_entry *res)
 {
 	struct rdma_restrack_entry *old;
 	struct rdma_restrack_root *rt;
@@ -332,24 +370,22 @@ void rdma_restrack_del(struct rdma_restrack_entry *res)
 		}
 		return;
 	}
-
-	if (res->no_track)
-		goto out;
+	res->valid = false;
 
 	dev = res_to_dev(res);
-	if (WARN_ON(!dev))
-		return;
-
 	rt = &dev->res[res->type];
-
 	old = xa_erase(&rt->xa, res->id);
-	if (res->type == RDMA_RESTRACK_MR || res->type == RDMA_RESTRACK_QP)
-		return;
-	WARN_ON(old != res);
+	WARN_ON(old != NULL);
+}
+EXPORT_SYMBOL(rdma_restrack_finish_del);
 
-out:
-	res->valid = false;
-	rdma_restrack_put(res);
-	wait_for_completion(&res->comp);
+/**
+ * rdma_restrack_del() - delete object from the reource tracking database
+ * @res:  resource entry
+ */
+void rdma_restrack_del(struct rdma_restrack_entry *res)
+{
+	rdma_restrack_prepare_del(res);
+	rdma_restrack_finish_del(res);
 }
 EXPORT_SYMBOL(rdma_restrack_del);
diff --git a/drivers/infiniband/core/restrack.h b/drivers/infiniband/core/restrack.h
index 6a04fc41f73801..87a670334acabe 100644
--- a/drivers/infiniband/core/restrack.h
+++ b/drivers/infiniband/core/restrack.h
@@ -27,6 +27,9 @@ int rdma_restrack_init(struct ib_device *dev);
 void rdma_restrack_clean(struct ib_device *dev);
 void rdma_restrack_add(struct rdma_restrack_entry *res);
 void rdma_restrack_del(struct rdma_restrack_entry *res);
+void rdma_restrack_prepare_del(struct rdma_restrack_entry *res);
+void rdma_restrack_finish_del(struct rdma_restrack_entry *res);
+void rdma_restrack_abort_del(struct rdma_restrack_entry *res);
 void rdma_restrack_new(struct rdma_restrack_entry *res,
 		       enum rdma_restrack_type type);
 void rdma_restrack_set_name(struct rdma_restrack_entry *res,
diff --git a/drivers/infiniband/core/verbs.c b/drivers/infiniband/core/verbs.c
index 2b0798151fb753..2e761a7eb92847 100644
--- a/drivers/infiniband/core/verbs.c
+++ b/drivers/infiniband/core/verbs.c
@@ -346,13 +346,16 @@ int ib_dealloc_pd_user(struct ib_pd *pd, struct ib_udata *udata)
 	 */
 	WARN_ON(atomic_read(&pd->usecnt));
 
+	rdma_restrack_prepare_del(&pd->res);
 	ret = pd->device->ops.dealloc_pd(pd, udata);
-	if (ret)
+	if (ret) {
+		rdma_restrack_abort_del(&pd->res);
 		return ret;
+	}
 
-	rdma_restrack_del(&pd->res);
+	rdma_restrack_finish_del(&pd->res);
 	kfree(pd);
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL(ib_dealloc_pd_user);
 
@@ -1085,19 +1088,22 @@ int ib_destroy_srq_user(struct ib_srq *srq, struct ib_udata *udata)
 	if (atomic_read(&srq->usecnt))
 		return -EBUSY;
 
+	rdma_restrack_prepare_del(&srq->res);
 	ret = srq->device->ops.destroy_srq(srq, udata);
-	if (ret)
+	if (ret) {
+		rdma_restrack_abort_del(&srq->res);
 		return ret;
+	}
+	rdma_restrack_finish_del(&srq->res);
 
 	atomic_dec(&srq->pd->usecnt);
 	if (srq->srq_type == IB_SRQT_XRC)
 		atomic_dec(&srq->ext.xrc.xrcd->usecnt);
 	if (ib_srq_has_cq(srq->srq_type))
 		atomic_dec(&srq->ext.cq->usecnt);
-	rdma_restrack_del(&srq->res);
 	kfree(srq);
 
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL(ib_destroy_srq_user);
 
@@ -1963,31 +1969,33 @@ int ib_destroy_qp_user(struct ib_qp *qp, struct ib_udata *udata)
 		rdma_rw_cleanup_mrs(qp);
 
 	rdma_counter_unbind_qp(qp, true);
-	rdma_restrack_del(&qp->res);
+	rdma_restrack_prepare_del(&qp->res);
 	ret = qp->device->ops.destroy_qp(qp, udata);
-	if (!ret) {
-		if (alt_path_sgid_attr)
-			rdma_put_gid_attr(alt_path_sgid_attr);
-		if (av_sgid_attr)
-			rdma_put_gid_attr(av_sgid_attr);
-		if (pd)
-			atomic_dec(&pd->usecnt);
-		if (scq)
-			atomic_dec(&scq->usecnt);
-		if (rcq)
-			atomic_dec(&rcq->usecnt);
-		if (srq)
-			atomic_dec(&srq->usecnt);
-		if (ind_tbl)
-			atomic_dec(&ind_tbl->usecnt);
-		if (sec)
-			ib_destroy_qp_security_end(sec);
-	} else {
+	if (ret) {
+		rdma_restrack_abort_del(&qp->res);
 		if (sec)
 			ib_destroy_qp_security_abort(sec);
+		return ret;
 	}
 
-	return ret;
+	rdma_restrack_finish_del(&qp->res);
+	if (alt_path_sgid_attr)
+		rdma_put_gid_attr(alt_path_sgid_attr);
+	if (av_sgid_attr)
+		rdma_put_gid_attr(av_sgid_attr);
+	if (pd)
+		atomic_dec(&pd->usecnt);
+	if (scq)
+		atomic_dec(&scq->usecnt);
+	if (rcq)
+		atomic_dec(&rcq->usecnt);
+	if (srq)
+		atomic_dec(&srq->usecnt);
+	if (ind_tbl)
+		atomic_dec(&ind_tbl->usecnt);
+	if (sec)
+		ib_destroy_qp_security_end(sec);
+	return 0;
 }
 EXPORT_SYMBOL(ib_destroy_qp_user);
 
@@ -2050,13 +2058,16 @@ int ib_destroy_cq_user(struct ib_cq *cq, struct ib_udata *udata)
 	if (atomic_read(&cq->usecnt))
 		return -EBUSY;
 
+	rdma_restrack_prepare_del(&cq->res);
 	ret = cq->device->ops.destroy_cq(cq, udata);
-	if (ret)
+	if (ret) {
+		rdma_restrack_abort_del(&cq->res);
 		return ret;
+	}
 
-	rdma_restrack_del(&cq->res);
+	rdma_restrack_finish_del(&cq->res);
 	kfree(cq);
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL(ib_destroy_cq_user);
 
@@ -2126,16 +2137,19 @@ int ib_dereg_mr_user(struct ib_mr *mr, struct ib_udata *udata)
 	int ret;
 
 	trace_mr_dereg(mr);
-	rdma_restrack_del(&mr->res);
+	rdma_restrack_prepare_del(&mr->res);
 	ret = mr->device->ops.dereg_mr(mr, udata);
-	if (!ret) {
-		atomic_dec(&pd->usecnt);
-		if (dm)
-			atomic_dec(&dm->usecnt);
-		kfree(sig_attrs);
+	if (ret) {
+		rdma_restrack_abort_del(&mr->res);
+		return ret;
 	}
 
-	return ret;
+	rdma_restrack_finish_del(&mr->res);
+	atomic_dec(&pd->usecnt);
+	if (dm)
+		atomic_dec(&dm->usecnt);
+	kfree(sig_attrs);
+	return 0;
 }
 EXPORT_SYMBOL(ib_dereg_mr_user);