Re: 6b41030fdc790 broke dmatest badly

[Vladimir Murzin <vladimir.murzin@arm.com>]

On 9/7/20 3:05 PM, Andy Shevchenko wrote:
> On Mon, Sep 07, 2020 at 02:06:23PM +0100, Vladimir Murzin wrote:
>> On 9/7/20 1:06 PM, Andy Shevchenko wrote:
>>> On Mon, Sep 07, 2020 at 12:03:26PM +0100, Vladimir Murzin wrote:
>>>> On 9/4/20 6:34 PM, Andy Shevchenko wrote:
>>>>> It becomes a bit annoying to fix dmatest after almost each release.
>>>>> The commit 6b41030fdc79 ("dmaengine: dmatest: Restore default for channel")
>>>>> broke my use case when I tried to start busy channel.
>>>>>
>>>>> So, before this patch
>>>>> 	...
>>>>> 	echo "busy_chan" > channel
>>>>> 	echo 1 > run
>>>>> 	sh: write error: Device or resource busy
>>>>> 	[ 1013.868313] dmatest: Could not start test, no channels configured
>>>>>
>>>>> After I have got it run on *ALL* available channels.
>>>>
>>>> Is not that controlled with max_channels? 
>>>
>>> How? I would like to run the test against specific channel. That channel is
>>> occupied and thus I should get an error. This is how it suppose to work and
>>> actually did before your patch.
>>
>> Since you highlighted "ALL" I though that was an issue, yet looks like you
>> expect run command would do nothing, correct?
> 
> Yes!
> 
>> IIUC attempt to add already occupied channel is producing error regardless of
>> my patch and I do not see how error could come from run command.
> 
> We need to save the status somewhere that the channel setter has been called
> unsuccessfully. And propagate an error to the run routine.

I'm not familiar with the code to propose nice and elegant solution, but for the
start (build only)

diff --git a/drivers/dma/dmatest.c b/drivers/dma/dmatest.c
index 45d4d92..40dba6b 100644
--- a/drivers/dma/dmatest.c
+++ b/drivers/dma/dmatest.c
@@ -129,6 +129,7 @@ struct dmatest_params {
  * @nr_channels:	number of channels under test
  * @lock:		access protection to the fields of this structure
  * @did_init:		module has been initialized completely
+ * @misconfig:		test has faced configuration issues
  */
 static struct dmatest_info {
 	/* Test parameters */
@@ -139,6 +140,7 @@ static struct dmatest_info {
 	unsigned int		nr_channels;
 	struct mutex		lock;
 	bool			did_init;
+	bool			misconfig;
 } test_info = {
 	.channels = LIST_HEAD_INIT(test_info.channels),
 	.lock = __MUTEX_INITIALIZER(test_info.lock),
@@ -1184,16 +1186,26 @@ static int dmatest_run_set(const char *val, const struct kernel_param *kp)
 		return ret;
 	} else if (dmatest_run) {
 		if (!is_threaded_test_pending(info)) {
-			pr_info("No channels configured, continue with any\n");
-			if (!is_threaded_test_run(info))
-				stop_threaded_test(info);
-			add_threaded_test(info);
+			/*
+			 * We have nothing to run. This can be due to:
+			 */
+			if (info->misconfig) {
+				/* 1) Mis-configuration */
+				pr_warn("Channels mis-configured, could not continue\n");
+				goto out;
+			} else {
+				/* 2) We rely on defaults */
+				pr_info("No channels configured, continue with any\n");
+				if (!is_threaded_test_run(info))
+					stop_threaded_test(info);
+				add_threaded_test(info);
+			}
 		}
 		start_threaded_tests(info);
 	} else {
 		stop_threaded_test(info);
 	}
-
+out:
 	mutex_unlock(&info->lock);
 
 	return ret;
@@ -1226,6 +1238,7 @@ static int dmatest_chan_set(const char *val, const struct kernel_param *kp)
 				strlcpy(chan_reset_val,
 					dma_chan_name(dtc->chan),
 					sizeof(chan_reset_val));
+				info->misconfig = true;
 				ret = -EBUSY;
 				goto add_chan_err;
 			}
@@ -1246,6 +1259,7 @@ static int dmatest_chan_set(const char *val, const struct kernel_param *kp)
 		 */
 		if ((strcmp(dma_chan_name(dtc->chan), strim(test_channel)) != 0)
 		    && (strcmp("", strim(test_channel)) != 0)) {
+			info->misconfig = true;
 			ret = -EINVAL;
 			strlcpy(chan_reset_val, dma_chan_name(dtc->chan),
 				sizeof(chan_reset_val));
@@ -1255,6 +1269,7 @@ static int dmatest_chan_set(const char *val, const struct kernel_param *kp)
 	} else {
 		/* Clear test_channel if no channels were added successfully */
 		strlcpy(chan_reset_val, "", sizeof(chan_reset_val));
+		info->misconfig = true;
 		ret = -EBUSY;
 		goto add_chan_err;
 	}

> 
>> As for my patch it restores behaviour of how it supposed to work prior d53513d5dc28
>> where run command would execute with default settings if under-configured.
> 
> Yeah, yet another breaking patch series (I have fixed one bug in that) which
> has been dumped and someone disappeared...
> 
> Yes, and here is a corner case. I have batch script which fills sysfs
> parameters with something meaningful. However, when error happens in channel
> setter the run kick off, luckily, b/c of regression you have noticed, doesn't
> happen.
> 
> And this behaviour as far as I remember was previously before the d53513d5dc28.
> At least I remember that I wrote my scripts few years ago and they worked.

Can we actually confirm behaviour before d53513d5dc28? That would add confidence
that we are doing right thing.

As for scripts it looks like folk have them covering different cases yet seems
not something run regularly, so should not we cooperate with kernel CI team or its
equivalent and try to get (some of?) them into their environment?

Cheers
Vladimir 

> 
>>>>> dmatest compiled as a module.
>>>>>
>>>>> Fix this ASAP, otherwise I will send revert of this and followed up patch next
>>>>> week.
>>>>
>>>> I don't quite get it, you are sending revert and then a fix rather then helping
>>>> with a fix?
>>>
>>> Correct.
>>>
>>>> What is reason for such extreme (and non-cooperative) flow?
>>>
>>> There are few reasons:
>>>  - the patch made a clear regression
>>>  - I do not understand what that patch is doing and how
>>>  - I do not have time to look at it
>>>  - we are now at v5.9-rc4 and it seems like one or two weeks time to get it
>>>    into v5.9 release
>>>  - and I'm annoyed by breaking this module not the first time for the last
>>>    couple of years
>>>
>>> And on top of that it's not how OSS community works. Since you replied, I give
>>> you time to figure out what's going on and provide necessary testing if needed.
>>>
>>>> P.S.
>>>> Unfortunately, I do not have access to hardware to run reproducer.
>>>
>>> So, please, propose a fix without it. I will test myself.
>>>
>>
>