linux-kernel - Re: [PATCH 1/2] of: unittest: option to allow tests that trigger kernel stack dump

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Message-ID: <96cfd1ee-768d-cc03-53dd-35ccf2396863@gmail.com>
Date:   Wed, 1 Mar 2023 10:01:36 -0600
From:   Frank Rowand <frowand.list@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Rob Herring <robh+dt@...nel.org>,
        Jonathan Corbet <corbet@....net>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH 1/2] of: unittest: option to allow tests that trigger
 kernel stack dump

On 2/28/23 22:07, Guenter Roeck wrote:
> On 2/28/23 17:21, Frank Rowand wrote:
>> Commit 74df14cd301a ("of: unittest: add node lifecycle tests") added
>> some tests that trigger a kernel stack dump.  Filtering the boot
>> messages with scripts/dtc/of_unittest_expect detects that the stack
>> dump is expected instead of being a test error.
>>
>> Test beds might interpret the stack dumps as errors, resulting in
>> needless debugging and error reports.  These test beds are likely
>> to remove unittests due to these stack dumps. To avoid these problems,
>> have unittest default to skip the tests that trigger a stack dump.
>>
>> Add a kernel cmdline option to not skip those tests.  This option can
>> be used by testers who are able to interpret the stack dumps as not
>> an error.
>>
>> Signed-off-by: Frank Rowand <frowand.list@...il.com>
>> ---
>>   drivers/of/unittest.c | 54 ++++++++++++++++++++++++++++++++++++++++---
>>   1 file changed, 51 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
>> index b5a7a31d8bd2..3a9bc2bc4ba1 100644
>> --- a/drivers/of/unittest.c
>> +++ b/drivers/of/unittest.c
>> @@ -70,6 +70,36 @@ static struct unittest_results {
>>   #define EXPECT_NOT_END(level, fmt, ...) \
>>       printk(level pr_fmt("EXPECT_NOT / : ") fmt, ##__VA_ARGS__)
>>   +/*
>> + * Some tests will cause the kernel to emit a stack dump, aka back trace,
>> + * when the test is successful.  The tests should make it possible for
>> + * test beds to detect that the trace is not an error via EXPECT_BEGIN().
>> + *
>> + * Most test beds do not process the EXPECT_BEGIN() information and may
>> + * flag the stack dump as an error, thus reporting a false failure.  It
>> + * is hoped that the KTAP version 4 specification will add the EXPECT_BEGIN()
>> + * processing to test beds.
>> + *
>> + * By default, skip tests that cause a stack dump.  Test beds that process
>> + * EXPECT_BEGIN() information should enable these tests via a kernel boot
>> + * command line option.
>> + */
>> +static int stackdump_tests_enabled;
>> +
>> +static int __init enable_unittest_stackdump(char *str)
>> +{
>> +    stackdump_tests_enabled = 1;
>> +    return 0;
>> +}
>> +
>> +static int __init disable_unittest_stackdump(char *str)
>> +{
>> +    stackdump_tests_enabled = 0;
>> +    return 0;
>> +}
>> +early_param("of_unittest_stackdump", enable_unittest_stackdump);
>> +early_param("no_of_unittest_stackdump", disable_unittest_stackdump);
> 
> Does no_of_unittest_stackdump have any benefit or value ?

I would say no, but it is a common pattern to provide both
foo and no_foo.

-Frank

> 
> Thanks,
> Guenter
>