ztest: Fix scrub check in ztest_raidz_expand_check()

The scrub code may return EBUSY under several possible scenarios
causing ztest to incorrectly ASSERT when verifying the result of
a raidz expansion.  Update the test case to allow EBUSY since it
does not indicate pool damage.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #16627

cmd/ztest.c

@@ -6717,6 +6717,17 @@ ztest_fault_inject(ztest_ds_t *zd, uint64_t id)
  *
  * Only after a full scrub has been completed is it safe to start injecting
  * data corruption.  See the comment in zfs_fault_inject().
+ *
+ * EBUSY may be returned for the following six cases.  It's the callers
+ * responsibility to handle them accordingly.
+ *
+ * Current state                Requested
+ * 1. Normal Scrub Running      Normal Scrub or Error Scrub
+ * 2. Normal Scrub Paused       Error Scrub
+ * 3. Normal Scrub Paused       Pause Normal Scrub
+ * 4. Error Scrub Running       Normal Scrub or Error Scrub
+ * 5. Error Scrub Paused        Pause Error Scrub
+ * 6. Resilvering               Anything else
  */
 static int
 ztest_scrub_impl(spa_t *spa)
@@ -8082,8 +8093,14 @@ ztest_raidz_expand_check(spa_t *spa)
 		(void) printf("verifying an interrupted raidz "
 		    "expansion using a pool scrub ...\n");
 	}
+
 	/* Will fail here if there is non-recoverable corruption detected */
-	VERIFY0(ztest_scrub_impl(spa));
+	int error = ztest_scrub_impl(spa);
+	if (error == EBUSY)
+		error = 0;
+
+	VERIFY0(error);
+
 	if (ztest_opts.zo_verbose >= 1) {
 		(void) printf("raidz expansion scrub check complete\n");
 	}

lib/libzfs/libzfs_pool.c

@@ -2796,7 +2796,7 @@ zpool_scan(zpool_handle_t *zhp, pool_scan_func_t func, pool_scrub_cmd_t cmd)
 	}
 
 	/*
-	 * With EBUSY, five cases are possible:
+	 * With EBUSY, six cases are possible:
 	 *
 	 * Current state		Requested
 	 * 1. Normal Scrub Running	Normal Scrub or Error Scrub