Merge pull request #1784 from thananon/fix_usnic_thread

Fix btl/usnic deadlock when the connectivity check is turned off.

opal/mca/btl/usnic/btl_usnic_cclient.c

@@ -229,12 +229,14 @@ int opal_btl_usnic_connectivity_ping(uint32_t src_ipv4_addr, int src_port,
                                      char *dest_nodename,
                                      size_t max_msg_size)
 {
-    OPAL_THREAD_LOCK(&btl_usnic_lock);
     /* If connectivity checking is not enabled, do nothing */
     if (!mca_btl_usnic_component.connectivity_enabled) {
         return OPAL_SUCCESS;
     }
 
+    /* Protect opal_fd_write for multithreaded case */
+    OPAL_THREAD_LOCK(&btl_usnic_lock);
+
     /* Send the PING command */
     int id = CONNECTIVITY_AGENT_CMD_PING;
     if (OPAL_SUCCESS != opal_fd_write(agent_fd, sizeof(id), &id)) {
@@ -260,6 +262,8 @@ int opal_btl_usnic_connectivity_ping(uint32_t src_ipv4_addr, int src_port,
         ABORT("usnic connectivity client IPC write failed");
         /* Will not return */
     }
+
+    /* Unlock and return */
     OPAL_THREAD_UNLOCK(&btl_usnic_lock);
 
     return OPAL_SUCCESS;