Re: Problems with csum_partial with misaligned buffers on sh4 platform

[Guenter Roeck]

Hi Adrian,

On 2/10/24 12:12, John Paul Adrian Glaubitz wrote:
> Hi Guenter,
>
> On Sat, 2024-02-10 at 07:12 -0800, Guenter Roeck wrote:
> > when running checksum unit tests on sh4 qemu emulations, I get the following
> > errors.
> >
> >      KTAP version 1
> >      # Subtest: checksum
> >      # module: checksum_kunit
> >      1..5
> >      # test_csum_fixed_random_inputs: ASSERTION FAILED at lib/checksum_kunit.c:500
> >      Expected ( u64)result == ( u64)expec, but
> >          ( u64)result == 53378 (0xd082)
> >          ( u64)expec == 33488 (0x82d0)
> >      not ok 1 test_csum_fixed_random_inputs
> >      # test_csum_all_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:525
> >      Expected ( u64)result == ( u64)expec, but
> >          ( u64)result == 65281 (0xff01)
> >          ( u64)expec == 65280 (0xff00)
> >      not ok 2 test_csum_all_carry_inputs
> >      # test_csum_no_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:573
> >      Expected ( u64)result == ( u64)expec, but
> >          ( u64)result == 65535 (0xffff)
> >          ( u64)expec == 65534 (0xfffe)
> >      not ok 3 test_csum_no_carry_inputs
> >      ok 4 test_ip_fast_csum
> >      ok 5 test_csum_ipv6_magic
> > # checksum: pass:2 fail:3 skip:0 total:5
> >
> > The above is with from a little endian system. On a big endian system,
> > the test result is as follows.
> >
> >      KTAP version 1
> >      # Subtest: checksum
> >      # module: checksum_kunit
> >      1..5
> >      # test_csum_fixed_random_inputs: ASSERTION FAILED at lib/checksum_kunit.c:500
> >      Expected ( u64)result == ( u64)expec, but
> >          ( u64)result == 33488 (0x82d0)
> >          ( u64)expec == 53378 (0xd082)
> >      not ok 1 test_csum_fixed_random_inputs
> >      # test_csum_all_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:525
> >      Expected ( u64)result == ( u64)expec, but
> >          ( u64)result == 65281 (0xff01)
> >          ( u64)expec == 255 (0xff)
> >      not ok 2 test_csum_all_carry_inputs
> >      # test_csum_no_carry_inputs: ASSERTION FAILED at lib/checksum_kunit.c:565
> >      Expected ( u64)result == ( u64)expec, but
> >          ( u64)result == 1020 (0x3fc)
> >          ( u64)expec == 0 (0x0)
> >      not ok 3 test_csum_no_carry_inputs
> >      # test_ip_fast_csum: ASSERTION FAILED at lib/checksum_kunit.c:589
> >      Expected ( u64)expected == ( u64)csum_result, but
> >          ( u64)expected == 55939 (0xda83)
> >          ( u64)csum_result == 33754 (0x83da)
> >      not ok 4 test_ip_fast_csum
> >      # test_csum_ipv6_magic: ASSERTION FAILED at lib/checksum_kunit.c:617
> >      Expected ( u64)expected_csum_ipv6_magic[i] == ( u64)csum_ipv6_magic(saddr, daddr, len, proto, csum), but
> >          ( u64)expected_csum_ipv6_magic[i] == 6356 (0x18d4)
> >          ( u64)csum_ipv6_magic(saddr, daddr, len, proto, csum) == 43586 (0xaa42)
> >      not ok 5 test_csum_ipv6_magic
> > # checksum: pass:0 fail:5 skip:0 total:5
> >
> > Note that test_ip_fast_csum and test_csum_ipv6_magic fail on all big endian
> > systems due to a bug in the test code, unrelated to this problem.
> >
> > Analysis shows that the errors are seen only if the buffer is misaligned.
> > Looking into arch/sh/lib/checksum.S, I found commit cadc4e1a2b4d2 ("sh:
> > Handle calling csum_partial with misaligned data") which seemed to be
> > related. Reverting that commit fixes the problem.
> > This suggests that something may be wrong with that commit. Alternatively,
> > of course, it may be possible that something is wrong with the qemu
> > emulation, but that seems unlikely.
>
> I have not run these tests before. Can you tell me how these are run,
> so I can verify these reproduce on real hardware?

Enabling CONFIG_KUNIT and CONFIG_CHECKSUM_KUNIT on top of a working
configuration should do the trick. Both can be built as module,
so presumably one can build and load them separately. I have not tried
that, though - I always build them into the kernel and boot the resulting
image.

Hope this helps,
Guenter