rcutorture: Add RCU grace-period performance tests

Hello Paul E. McKenney,

This is a semi-automatic email about new static checker warnings.

The patch 7f68f317a3d9: "rcutorture: Add RCU grace-period performance tests" from Dec 31, 2015, leads to the following Smatch complaint:

kernel/rcu/rcuperf.c:486 rcu_perf_cleanup()
error: we previously assumed 'writer_n_durations' could be null (see line 465)

kernel/rcu/rcuperf.c

   442  static void
   443  rcu_perf_cleanup(void)
   444  {
   445          int i;
   446          int j;
   447          int ngps = 0;
   448          u64 *wdp;
   449          u64 *wdpp;
   450  
   451          if (torture_cleanup_begin())
   452                  return;
   453  
   454          if (reader_tasks) {
   455                  for (i = 0; i < nrealreaders; i++)
   456                          torture_stop_kthread(rcu_perf_reader,
   457                                               reader_tasks[i]);
   458                  kfree(reader_tasks);
   459          }
   460  
   461          if (writer_tasks) {
   462                  for (i = 0; i < nrealwriters; i++) {
   463                          torture_stop_kthread(rcu_perf_writer,
   464						     writer_tasks[i]);
   465				if (!writer_n_durations)
                                     ^^^^^^^^^^^^^^^^^^

Can be NULL here.

466 continue;
467 j = writer_n_durations[i];
468 pr_alert("%s%s writer %d gps: %d\n",
469 perf_type, PERF_FLAG, i, j);
470 ngps += j;
471 }
472 pr_alert("%s%s start: %llu end: %llu duration: %llu gps: %d batches: %ld\n",
473 perf_type, PERF_FLAG,
474 t_rcu_perf_writer_started, t_rcu_perf_writer_finished,
475 t_rcu_perf_writer_finished -
476 t_rcu_perf_writer_started,
477 ngps,
478 b_rcu_perf_writer_finished -
479 b_rcu_perf_writer_started);
480 for (i = 0; i < nrealwriters; i++) {
481 if (!writer_durations)
482 break;
483 wdpp = writer_durations[i];
484 if (!wdpp)
485 continue;

   486				for (j = 0; j <= writer_n_durations[i]; j++) {
                                                 ^^^^^^^^^^^^^^^^^^^^^

Unchecked dereference.

487 wdp = &wdpp[j];
488 pr_alert("%s%s %4d writer-duration: %5d %llu\n",

regards,
dan carpenter

Good catch! Would the following cover it?

Thanx, Paul

------------------------------------------------------------------------

index c110298b76e6..1d88f1347301 100644
@@ -489,6 +489,8 @@ rcu_perf_cleanup(void)
 		for (i = 0; i < nrealwriters; i++) {
 			if (!writer_durations)
 				break;
+			if (!writer_n_durations)
+				continue;
 			wdpp = writer_durations[i];
 			if (!wdpp)
 				continue;

Looks good to me.

regards,
dan carpenter