dmatest: do not allow to interrupt ongoing tests

When user interrupts ongoing transfers the dmatest may end up with console
lockup, oops, or data mismatch. This patch prevents user to abort any ongoing
test.

Documentation is updated accordingly.

Signed-off-by: Andy Shevchenko <[e-mail]>
Reported-by: Will Deacon <[e-mail]>
Tested-by: Will Deacon <[e-mail]>
Signed-off-by: Vinod Koul <[e-mail]>

Documentation/dmatest.txt

···
 After a while you will start to get messages about current status or error like
 in the original code.
 
-Note that running a new test will stop any in progress test.
+Note that running a new test will not stop any in progress test.
 
 The following command should return actual state of the test.
 	% cat /sys/kernel/debug/dmatest/run
···
 
 The module parameters that is supplied to the kernel command line will be used
 for the first performed test. After user gets a control, the test could be
-interrupted or re-run with same or different parameters. For the details see
-the above section "Part 2 - When dmatest is built as a module..."
+re-run with the same or different parameters. For the details see the above
+section "Part 2 - When dmatest is built as a module..."
 
 In both cases the module parameters are used as initial values for the test case.
 You always could check them at run-time by running

drivers/dma/dmatest.c

···
 		}
 		dma_async_issue_pending(chan);
 
-		wait_event_freezable_timeout(done_wait,
-					     done.done || kthread_should_stop(),
+		wait_event_freezable_timeout(done_wait, done.done,
 					     msecs_to_jiffies(params->timeout));
 
 		status = dma_async_is_tx_complete(chan, cookie, NULL, NULL);
···
 static int __restart_threaded_test(struct dmatest_info *info, bool run)
 {
 	struct dmatest_params *params = &info->params;
-	int ret;
 
 	/* Stop any running test first */
 	__stop_threaded_test(info);
···
 	memcpy(params, &info->dbgfs_params, sizeof(*params));
 
 	/* Run test with new parameters */
-	ret = __run_threaded_test(info);
-	if (ret) {
-		__stop_threaded_test(info);
-		pr_err("dmatest: Can't run test\n");
+	return __run_threaded_test(info);
+}
+
+static bool __is_threaded_test_run(struct dmatest_info *info)
+{
+	struct dmatest_chan *dtc;
+
+	list_for_each_entry(dtc, &info->channels, node) {
+		struct dmatest_thread *thread;
+
+		list_for_each_entry(thread, &dtc->threads, node) {
+			if (!thread->done)
+				return true;
+		}
 	}
 
-	return ret;
+	return false;
 }
 
 static ssize_t dtf_write_string(void *to, size_t available, loff_t *ppos,
···
 {
 	struct dmatest_info *info = file->private_data;
 	char buf[3];
-	struct dmatest_chan *dtc;
-	bool alive = false;
 
 	mutex_lock(&info->lock);
-	list_for_each_entry(dtc, &info->channels, node) {
-		struct dmatest_thread *thread;
 
-		list_for_each_entry(thread, &dtc->threads, node) {
-			if (!thread->done) {
-				alive = true;
-				break;
-			}
-		}
-	}
-
-	if (alive) {
+	if (__is_threaded_test_run(info)) {
 		buf[0] = 'Y';
 	} else {
 		__stop_threaded_test(info);
···
 
 	if (strtobool(buf, &bv) == 0) {
 		mutex_lock(&info->lock);
-		ret = __restart_threaded_test(info, bv);
+
+		if (__is_threaded_test_run(info))
+			ret = -EBUSY;
+		else
+			ret = __restart_threaded_test(info, bv);
+
 		mutex_unlock(&info->lock);
 	}