target/iscsi: Fix network portal creation race

When creating network portals rapidly, such as when restoring a
configuration, LIO's code to reuse existing portals can return a false
negative if the thread hasn't run yet and set np_thread_state to
ISCSI_NP_THREAD_ACTIVE. This causes an error in the network stack
when attempting to bind to the same address/port.

This patch sets NP_THREAD_ACTIVE before the np is placed on g_np_list,
so even if the thread hasn't run yet, iscsit_get_np will return the
existing np.

Also, convert np_lock -> np_mutex + hold across adding new net portal
to g_np_list to prevent a race where two threads may attempt to create
the same network portal, resulting in one of them failing.

(nab: Add missing mutex_unlocks in iscsit_add_np failure paths)
(DanC: Fix incorrect spin_unlock -> spin_unlock_bh)

Signed-off-by: Andy Grover <agrover@redhat.com>
Cc: <stable@vger.kernel.org> #3.1+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/iscsi/iscsi_target.c

@@ -52,7 +52,7 @@
 static LIST_HEAD(g_tiqn_list);
 static LIST_HEAD(g_np_list);
 static DEFINE_SPINLOCK(tiqn_lock);
-static DEFINE_SPINLOCK(np_lock);
+static DEFINE_MUTEX(np_lock);
 
 static struct idr tiqn_idr;
 struct idr sess_idr;
@@ -307,6 +307,9 @@ bool iscsit_check_np_match(
 	return false;
 }
 
+/*
+ * Called with mutex np_lock held
+ */
 static struct iscsi_np *iscsit_get_np(
 	struct __kernel_sockaddr_storage *sockaddr,
 	int network_transport)
@@ -314,11 +317,10 @@ static struct iscsi_np *iscsit_get_np(
 	struct iscsi_np *np;
 	bool match;
 
-	spin_lock_bh(&np_lock);
 	list_for_each_entry(np, &g_np_list, np_list) {
-		spin_lock(&np->np_thread_lock);
+		spin_lock_bh(&np->np_thread_lock);
 		if (np->np_thread_state != ISCSI_NP_THREAD_ACTIVE) {
-			spin_unlock(&np->np_thread_lock);
+			spin_unlock_bh(&np->np_thread_lock);
 			continue;
 		}
 
@@ -330,13 +332,11 @@ static struct iscsi_np *iscsit_get_np(
 			 * while iscsi_tpg_add_network_portal() is called.
 			 */
 			np->np_exports++;
-			spin_unlock(&np->np_thread_lock);
-			spin_unlock_bh(&np_lock);
+			spin_unlock_bh(&np->np_thread_lock);
 			return np;
 		}
-		spin_unlock(&np->np_thread_lock);
+		spin_unlock_bh(&np->np_thread_lock);
 	}
-	spin_unlock_bh(&np_lock);
 
 	return NULL;
 }
@@ -350,16 +350,22 @@ struct iscsi_np *iscsit_add_np(
 	struct sockaddr_in6 *sock_in6;
 	struct iscsi_np *np;
 	int ret;
+
+	mutex_lock(&np_lock);
+
 	/*
 	 * Locate the existing struct iscsi_np if already active..
 	 */
 	np = iscsit_get_np(sockaddr, network_transport);
-	if (np)
+	if (np) {
+		mutex_unlock(&np_lock);
 		return np;
+	}
 
 	np = kzalloc(sizeof(struct iscsi_np), GFP_KERNEL);
 	if (!np) {
 		pr_err("Unable to allocate memory for struct iscsi_np\n");
+		mutex_unlock(&np_lock);
 		return ERR_PTR(-ENOMEM);
 	}
 
@@ -382,6 +388,7 @@ struct iscsi_np *iscsit_add_np(
 	ret = iscsi_target_setup_login_socket(np, sockaddr);
 	if (ret != 0) {
 		kfree(np);
+		mutex_unlock(&np_lock);
 		return ERR_PTR(ret);
 	}
 
@@ -390,6 +397,7 @@ struct iscsi_np *iscsit_add_np(
 		pr_err("Unable to create kthread: iscsi_np\n");
 		ret = PTR_ERR(np->np_thread);
 		kfree(np);
+		mutex_unlock(&np_lock);
 		return ERR_PTR(ret);
 	}
 	/*
@@ -400,10 +408,10 @@ struct iscsi_np *iscsit_add_np(
 	 * point because iscsi_np has not been added to g_np_list yet.
 	 */
 	np->np_exports = 1;
+	np->np_thread_state = ISCSI_NP_THREAD_ACTIVE;
 
-	spin_lock_bh(&np_lock);
 	list_add_tail(&np->np_list, &g_np_list);
-	spin_unlock_bh(&np_lock);
+	mutex_unlock(&np_lock);
 
 	pr_debug("CORE[0] - Added Network Portal: %s:%hu on %s\n",
 		np->np_ip, np->np_port, np->np_transport->name);
@@ -469,9 +477,9 @@ int iscsit_del_np(struct iscsi_np *np)
 
 	np->np_transport->iscsit_free_np(np);
 
-	spin_lock_bh(&np_lock);
+	mutex_lock(&np_lock);
 	list_del(&np->np_list);
-	spin_unlock_bh(&np_lock);
+	mutex_unlock(&np_lock);
 
 	pr_debug("CORE[0] - Removed Network Portal: %s:%hu on %s\n",
 		np->np_ip, np->np_port, np->np_transport->name);