Handle interrupted kthread_create() and ENOMEM failures.

Kernels >= 3.13 can return ENOMEM from kthread_create() in both a true
out of memory situation and also if the call is interrupted.  Re-try
the kthread_create() in these cases.

module/spl/spl-taskq.c

@@ -839,16 +839,26 @@ taskq_create(const char *name, int nthreads, pri_t pri,
 		tqt->tqt_tq = tq;
 		tqt->tqt_id = 0;
 
+	restart:
 		tqt->tqt_thread = kthread_create(taskq_thread, tqt,
 		    "%s/%d", name, i);
-		if (tqt->tqt_thread) {
+		if (IS_ERR(tqt->tqt_thread)) {
+			/* Re-try on interrupted kthread_create() */
+			if (signal_pending(current)) {
+				clear_thread_flag(TIF_SIGPENDING);
+				goto restart;
+			}
+			/* Re-try on a "real" ENOMEM */
+			if (PTR_ERR(tqt->tqt_thread) == -ENOMEM) {
+				goto restart;
+			}
+			/* Return NULL on any other error */
+			rc = 1;
+		} else {
 			list_add(&tqt->tqt_thread_list, &tq->tq_thread_list);
 			set_user_nice(tqt->tqt_thread, PRIO_TO_NICE(pri));
 			wake_up_process(tqt->tqt_thread);
 			j++;
-		} else {
-			kmem_free(tqt, sizeof(taskq_thread_t));
-			rc = 1;
 		}
 	}
 

module/spl/spl-thread.c

@@ -126,9 +126,12 @@ __thread_create(caddr_t stk, size_t  stksize, thread_func_t func,
 	tp->tp_state = state;
 	tp->tp_pri   = pri;
 
+retry:
 	tsk = kthread_create(thread_generic_wrapper, (void *)tp,
 			     "%s", tp->tp_name);
 	if (IS_ERR(tsk)) {
+		if (PTR_ERR(tsk) == -ENOMEM)
+			goto retry;
 		SERROR("Failed to create thread: %ld\n", PTR_ERR(tsk));
 		SRETURN(NULL);
 	}