IB/srp: Avoid duplicate connections

The connection uniqueness check is performed before a new connection
is added to the target list. This patch protects both actions by a
mutex such that simultaneous writes from two different threads into the
"add_target" variable do not result in duplicate connections.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/ulp/srp/ib_srp.c

@@ -2614,6 +2614,8 @@ static ssize_t srp_create_target(struct device *dev,
 	target->tl_retry_count	= 7;
 	target->queue_size	= SRP_DEFAULT_QUEUE_SIZE;
 
+	mutex_lock(&host->add_target_mutex);
+
 	ret = srp_parse_options(buf, target);
 	if (ret)
 		goto err;
@@ -2682,7 +2684,11 @@ static ssize_t srp_create_target(struct device *dev,
 		     be64_to_cpu(target->service_id),
 		     target->path.sgid.raw, target->path.dgid.raw);
 
-	return count;
+	ret = count;
+
+out:
+	mutex_unlock(&host->add_target_mutex);
+	return ret;
 
 err_disconnect:
 	srp_disconnect_target(target);
@@ -2698,8 +2704,7 @@ static ssize_t srp_create_target(struct device *dev,
 
 err:
 	scsi_host_put(target_host);
-
-	return ret;
+	goto out;
 }
 
 static DEVICE_ATTR(add_target, S_IWUSR, NULL, srp_create_target);
@@ -2735,6 +2740,7 @@ static struct srp_host *srp_add_port(struct srp_device *device, u8 port)
 	INIT_LIST_HEAD(&host->target_list);
 	spin_lock_init(&host->target_lock);
 	init_completion(&host->released);
+	mutex_init(&host->add_target_mutex);
 	host->srp_dev = device;
 	host->port = port;
 

drivers/infiniband/ulp/srp/ib_srp.h

@@ -105,6 +105,7 @@ struct srp_host {
 	spinlock_t		target_lock;
 	struct completion	released;
 	struct list_head	list;
+	struct mutex		add_target_mutex;
 };
 
 struct srp_request {