Fix issue with backfill scheduler scheduling tasks of an array

when not the head job.

Bug 6837

For more in depth explanation see comment 24

NEWS

@@ -24,6 +24,8 @@ documents those changes that are of interest to users and administrators.
  -- Fix potential deadlock with backup slurmctld.
  -- Fixed issue with jobs not appearing in sacct after dependency satisfied.
  -- Fix showing non-eligible jobs when asking with -j and not -s.
+ -- Fix issue with backfill scheduler scheduling tasks of an array
+    when not the head job.
 
 * Changes in Slurm 18.08.7
 ==========================

src/plugins/sched/backfill/backfill.c

@@ -1333,7 +1333,7 @@ static int _attempt_backfill(void)
 	uint32_t test_array_job_id = 0;
 	uint32_t test_array_count = 0;
 	uint32_t job_no_reserve;
-	bool resv_overlap = false;
+	bool is_job_array_head, resv_overlap = false;
 	uint8_t save_share_res = 0, save_whole_node = 0;
 	int test_fini;
 	int user_part_inx1 = -1, user_part_inx2 = -1;
@@ -1699,6 +1699,11 @@ static int _attempt_backfill(void)
 		orig_start_time = job_ptr->start_time;
 		orig_time_limit = job_ptr->time_limit;
 
+		if (job_ptr->array_recs && (job_ptr->array_task_id == NO_VAL))
+			is_job_array_head = true;
+		else
+			is_job_array_head = false;
+
 next_task:
 		/*
 		 * Save the current preemption state. Reset preemption state
@@ -2444,11 +2449,15 @@ static int _attempt_backfill(void)
 					}
 					break;
 				}
-				if (job_ptr->array_task_id != NO_VAL) {
+				if (is_job_array_head &&
+				    (job_ptr->array_task_id != NO_VAL)) {
 					/* Try starting next task of job array */
 					job_ptr = find_job_record(job_ptr->
 								  array_job_id);
-					if (job_ptr && IS_JOB_PENDING(job_ptr))
+					if (job_ptr &&
+					    IS_JOB_PENDING(job_ptr) &&
+					    (bb_g_job_test_stage_in(
+						    job_ptr, false) == 1))
 						goto next_task;
 				}
 				continue;