ztest: Fix false positive of ENOSPC handling

Before running a pass zs_enospc_count is checked to free up some space
by destroying a random dataset. But the space freed may still be not
re-usable during the TXG_DEFER window breaking the next dataset creation
in ztest_generic_run().
    
Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Igor Ostapenko <[email protected]>
Closes #17506

Author: ihoro

cmd/ztest.c

@@ -7812,6 +7812,9 @@ ztest_dataset_open(int d)
 
 	ztest_dataset_name(name, ztest_opts.zo_pool, d);
 
+	if (ztest_opts.zo_verbose >= 6)
+		(void) printf("Opening %s\n", name);
+
 	(void) pthread_rwlock_rdlock(&ztest_name_lock);
 
 	error = ztest_dataset_create(name);
@@ -8307,41 +8310,44 @@ static void
 ztest_generic_run(ztest_shared_t *zs, spa_t *spa)
 {
 	kthread_t **run_threads;
-	int t;
+	int i, ndatasets;
 
 	run_threads = umem_zalloc(ztest_opts.zo_threads * sizeof (kthread_t *),
 	    UMEM_NOFAIL);
 
 	/*
-	 * Kick off all the tests that run in parallel.
+	 * Actual number of datasets to be used.
 	 */
-	for (t = 0; t < ztest_opts.zo_threads; t++) {
-		if (t < ztest_opts.zo_datasets && ztest_dataset_open(t) != 0) {
-			umem_free(run_threads, ztest_opts.zo_threads *
-			    sizeof (kthread_t *));
-			return;
-		}
+	ndatasets = MIN(ztest_opts.zo_datasets, ztest_opts.zo_threads);
+
+	/*
+	 * Prepare the datasets first.
+	 */
+	for (i = 0; i < ndatasets; i++)
+		VERIFY0(ztest_dataset_open(i));
 
-		run_threads[t] = thread_create(NULL, 0, ztest_thread,
-		    (void *)(uintptr_t)t, 0, NULL, TS_RUN | TS_JOINABLE,
+	/*
+	 * Kick off all the tests that run in parallel.
+	 */
+	for (i = 0; i < ztest_opts.zo_threads; i++) {
+		run_threads[i] = thread_create(NULL, 0, ztest_thread,
+		    (void *)(uintptr_t)i, 0, NULL, TS_RUN | TS_JOINABLE,
 		    defclsyspri);
 	}
 
 	/*
 	 * Wait for all of the tests to complete.
 	 */
-	for (t = 0; t < ztest_opts.zo_threads; t++)
-		VERIFY0(thread_join(run_threads[t]));
+	for (i = 0; i < ztest_opts.zo_threads; i++)
+		VERIFY0(thread_join(run_threads[i]));
 
 	/*
 	 * Close all datasets. This must be done after all the threads
 	 * are joined so we can be sure none of the datasets are in-use
 	 * by any of the threads.
 	 */
-	for (t = 0; t < ztest_opts.zo_threads; t++) {
-		if (t < ztest_opts.zo_datasets)
-			ztest_dataset_close(t);
-	}
+	for (i = 0; i < ndatasets; i++)
+		ztest_dataset_close(i);
 
 	txg_wait_synced(spa_get_dsl(spa), 0);
 
@@ -8464,6 +8470,7 @@ ztest_run(ztest_shared_t *zs)
 
 		int d = ztest_random(ztest_opts.zo_datasets);
 		ztest_dataset_destroy(d);
+		txg_wait_synced(spa_get_dsl(spa), 0);
 	}
 	zs->zs_enospc_count = 0;