Message-ID: <aUPNpGgj3hmA3aZL@li-dc0c254c-257c-11b2-a85c-98b6c1322444.ibm.com>
Date: Thu, 18 Dec 2025 15:17:16 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: David Gow <davidgow@...gle.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, Dec 18, 2025 at 04:58:33PM +0800, David Gow wrote:
> 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

Hi David,

Thanks for the workaround, KUNIT_CASE_PARAM_WITH_INIT() did the trick!

So I'm just wondering if it makes sense to still have a placeholder test
plan line in cases we can't determine the number of tests. I think something
like 1..X should be enough to not throw off the parsing. (Although I
think this might not be exactly compliant to KTAP).

Regards,
ojaswin

> 
> > >     # 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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