RDMA/srpt: Rework the approach for closing an RDMA channel

Instead of relying on a waitqueue, report when the identity of an RDMA
channel can be reused through a completion.

Link: https://lore.kernel.org/r/20190930231707.48259-13-bvanassche@acm.org
Cc: Honggang LI <honli@redhat.com>
Cc: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/ulp/srpt/ib_srpt.c

@@ -1928,41 +1928,22 @@ static int srpt_disconnect_ch(struct srpt_rdma_ch *ch)
 	return ret;
 }
 
-static bool srpt_ch_closed(struct srpt_port *sport, struct srpt_rdma_ch *ch)
-{
-	struct srpt_nexus *nexus;
-	struct srpt_rdma_ch *ch2;
-	bool res = true;
-
-	rcu_read_lock();
-	list_for_each_entry(nexus, &sport->nexus_list, entry) {
-		list_for_each_entry(ch2, &nexus->ch_list, list) {
-			if (ch2 == ch) {
-				res = false;
-				goto done;
-			}
-		}
-	}
-done:
-	rcu_read_unlock();
-
-	return res;
-}
-
 /* Send DREQ and wait for DREP. */
 static void srpt_disconnect_ch_sync(struct srpt_rdma_ch *ch)
 {
+	DECLARE_COMPLETION_ONSTACK(closed);
 	struct srpt_port *sport = ch->sport;
 
 	pr_debug("ch %s-%d state %d\n", ch->sess_name, ch->qp->qp_num,
 		 ch->state);
 
+	ch->closed = &closed;
+
 	mutex_lock(&sport->mutex);
 	srpt_disconnect_ch(ch);
 	mutex_unlock(&sport->mutex);
 
-	while (wait_event_timeout(sport->ch_releaseQ, srpt_ch_closed(sport, ch),
-				  5 * HZ) == 0)
+	while (wait_for_completion_timeout(&closed, 5 * HZ) == 0)
 		pr_info("%s(%s-%d state %d): still waiting ...\n", __func__,
 			ch->sess_name, ch->qp->qp_num, ch->state);
 
@@ -2089,6 +2070,9 @@ static void srpt_release_channel_work(struct work_struct *w)
 	list_del_rcu(&ch->list);
 	mutex_unlock(&sport->mutex);
 
+	if (ch->closed)
+		complete(ch->closed);
+
 	srpt_destroy_ch_ib(ch);
 
 	srpt_free_ioctx_ring((struct srpt_ioctx **)ch->ioctx_ring,

drivers/infiniband/ulp/srpt/ib_srpt.h

@@ -264,6 +264,8 @@ enum rdma_ch_state {
  * @zw_cqe:	   Zero-length write CQE.
  * @rcu:           RCU head.
  * @kref:	   kref for this channel.
+ * @closed:	   Completion object that will be signaled as soon as a new
+ *		   channel object with the same identity can be created.
  * @rq_size:       IB receive queue size.
  * @max_rsp_size:  Maximum size of an RSP response message in bytes.
  * @sq_wr_avail:   number of work requests available in the send queue.
@@ -306,6 +308,7 @@ struct srpt_rdma_ch {
 	struct ib_cqe		zw_cqe;
 	struct rcu_head		rcu;
 	struct kref		kref;
+	struct completion	*closed;
 	int			rq_size;
 	u32			max_rsp_size;
 	atomic_t		sq_wr_avail;