Message-ID: <CABVgOSk5UJf00=uEsk4chEJpKoPeYqXbk+czM7ipoD_0eWiedg@mail.gmail.com>
Date: Thu, 18 Dec 2025 16:58:33 +0800
From: David Gow <davidgow@...gle.com>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc: linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com, 
	Shuah Khan <skhan@...uxfoundation.org>, Brendan Higgins <brendan.higgins@...ux.dev>, 
	Rae Moar <raemoar63@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: Issue in parsing of tests that use KUNIT_CASE_PARAM

On Thu, 18 Dec 2025 at 15:20, Ojaswin Mujoo <ojaswin@...ux.ibm.com> wrote:
>
> On Wed, Dec 17, 2025 at 08:47:57PM +0530, Ojaswin Mujoo wrote:
> > Hello,
> >
> > While writing some Kunit tests for ext4 filesystem, I'm encountering an
> > issue in the way we display the diagnostic logs upon failures, when
> > using KUNIT_CASE_PARAM() to write the tests.
> >
> > This can be observed by patching fs/ext4/mballoc-test.c to fail
> > and print one of the params:
> >
> > --- a/fs/ext4/mballoc-test.c
> > +++ b/fs/ext4/mballoc-test.c
> > @@ -350,6 +350,8 @@ static int mbt_kunit_init(struct kunit *test)
> >         struct super_block *sb;
> >         int ret;
> >
> > +       KUNIT_FAIL(test, "Failed: blocksize_bits=%d", layout->blocksize_bits);
> > +
> >         sb = mbt_ext4_alloc_super_block();
> >         if (sb == NULL)
> >                 return -ENOMEM;
> >
> > With the above change, we can observe the following output (snipped):
> >
> > [18:50:25] ============== ext4_mballoc_test (7 subtests) ==============
> > [18:50:25] ================= test_new_blocks_simple  ==================
> > [18:50:25] [FAILED] block_bits=10 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
> > [18:50:25]     # test_new_blocks_simple: EXPECTATION FAILED at fs/ext4/mballoc-test.c:364
> > [18:50:25] Failed: blocksize_bits=12
> > [18:50:25] [FAILED] block_bits=12 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
> > [18:50:25]     # test_new_blocks_simple: EXPECTATION FAILED at fs/ext4/mballoc-test.c:364
> > [18:50:25] Failed: blocksize_bits=16
> > [18:50:25] [FAILED] block_bits=16 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
> > [18:50:25]     # test_new_blocks_simple: EXPECTATION FAILED at fs/ext4/mballoc-test.c:364
> > [18:50:25] Failed: blocksize_bits=10
> > [18:50:25]     # test_new_blocks_simple: pass:0 fail:3 skip:0 total:3
> > [18:50:25] ============= [FAILED] test_new_blocks_simple ==============
> > <snip>
> >
> > Note that the diagnostic logs don't show up correctly. Ideally they
> > should be before test result but here the first [FAILED] test has no
> > logs printed above whereas the last "Failed: blocksize_bits=10" print
> > comes after the last subtest, when it actually corresponds to the first
> > subtest.
> >
> > The KTAP file itself seems to have diagnostic logs in the right place:
> >
> > KTAP version 1
> > 1..2
> >     KTAP version 1
> >     # Subtest: ext4_mballoc_test
> >     # module: ext4
> >     1..7
> >         KTAP version 1
> >         # Subtest: test_new_blocks_simple
>
> So looking into this a bit more and comparing the parameterized output
> with non parameterized output, I'm seeing that the difference is that
> output via KUNIT_CASE_PARAM is not printing the test plan line right
> here. This plan sort of serves as divider between the parent and the 3
> children's logs and without it our parsing logic gets confused. When I
> manually added a "1..3" test plan I could see the parsing work correctly
> without any changes to kunit_parser.py.
>

Thanks for looking into this!

There's been a bit of back-and-forth on how to include the test plan
line for the parameterised tests: it's not always possible to know how
many times a test will run in advance if the gen_params function is
particularly complicated.

We did have a workaround where array parameters would record the array
size, but there were a couple of tests which were wrapping the
gen_params function to skip / add entries which weren't in the array.

One "fix" would be to use KUNIT_CASE_PARAM_WITH_INIT() and have an
init function which calls kunit_register_params_array(), and then use
kunit_array_gen_params() as the generator function: this has an escape
hatch which will print the test plan.

Otherwise, as a hack, you could effectively revert
https://lore.kernel.org/linux-kselftest/20250821135447.1618942-2-davidgow@google.com/
— which would fix the issue (but break some other tests).

Going through and fixing this properly has been on my to-do list; with
some combination of fixing tests which modify the gen_params function
and improving the parsing to better handle cases without the test
plan.

Cheers,
-- David

> >     # test_new_blocks_simple: EXPECTATION FAILED at fs/ext4/mballoc-test.c:364
> > Failed: blocksize_bits=10
> >         not ok 1 block_bits=10 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
> >     # test_new_blocks_simple: EXPECTATION FAILED at fs/ext4/mballoc-test.c:364
> > Failed: blocksize_bits=12
> >         not ok 2 block_bits=12 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
> >     # test_new_blocks_simple: EXPECTATION FAILED at fs/ext4/mballoc-test.c:364
> > Failed: blocksize_bits=16
> >         not ok 3 block_bits=16 cluster_bits=3 blocks_per_group=8192 group_count=4 desc_size=64
> >     # test_new_blocks_simple: pass:0 fail:3 skip:0 total:3
> >     not ok 1 test_new_blocks_simple
> >     <snip>
> >
> > By tracing kunit_parser.py script, I could see the issue here is in the
> > parsing of the "Subtest: test_new_blocks_simple". We end up associating
> > everything below the subtest till "not ok 1 block_bits=10..." as
> > diagnostic logs of the subtest, while these lons actually belong to the
> > first of the 3 subtests under this test.
> >

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