[process] Make it safe to call process_add() multiple times

src/core/process.c

  * Add process to process list
  *
  * @v process		Process
+ *
+ * It is safe to call process_add() multiple times; further calls will
+ * have no effect.
  */
 void process_add ( struct process *process ) {
-	DBGC ( process, "PROCESS %p starting\n", process );
-	ref_get ( process->refcnt );
-	list_add_tail ( &process->list, &run_queue );
+	if ( list_empty ( &process->list ) ) {
+		DBGC ( process, "PROCESS %p starting\n", process );
+		ref_get ( process->refcnt );
+		list_add_tail ( &process->list, &run_queue );
+	} else {
+		DBGC ( process, "PROCESS %p already started\n", process );
+	}
 }
 
 /**

src/include/gpxe/process.h

 process_init_stopped ( struct process *process,
 		       void ( * step ) ( struct process *process ),
 		       struct refcnt *refcnt ) {
+	INIT_LIST_HEAD ( &process->list );
 	process->step = step;
 	process->refcnt = refcnt;
 }

src/net/infiniband.c

 
 /** Infiniband event queue process */
 struct process ib_process __permanent_process = {
+	.list = LIST_HEAD_INIT ( ib_process.list ),
 	.step = ib_step,
 };
 

src/net/netdevice.c

 
 /** Networking stack process */
 struct process net_process __permanent_process = {
+	.list = LIST_HEAD_INIT ( net_process.list ),
 	.step = net_step,
 };

src/net/retry.c

 
 /** Retry timer process */
 struct process retry_process __permanent_process = {
+	.list = LIST_HEAD_INIT ( retry_process.list ),
 	.step = retry_step,
 };