linux-kernel - Re: Problems with csum_partial with misaligned buffers on sh4 platform

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Date: Mon, 18 Mar 2024 16:04:11 +0100
From: "Linux regression tracking (Thorsten Leemhuis)"
 <regressions@...mhuis.info>
To: Guenter Roeck <linux@...ck-us.net>,
 Yoshinori Sato <ysato@...rs.sourceforge.jp>
Cc: Rich Felker <dalias@...c.org>,
 John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
 linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org,
 regressions@...ts.linux.dev
Subject: Re: Problems with csum_partial with misaligned buffers on sh4
 platform

On 11.03.24 18:04, Guenter Roeck wrote:
> On Sat, Feb 10, 2024 at 07:12:39AM -0800, Guenter Roeck wrote:
>>
>> when running checksum unit tests on sh4 qemu emulations, I get the following
>> errors.
> 
> Adding to regression tracker.
> 
> #regzbot ^introduced cadc4e1a2b4d2

Hmmm, thx for that, but well, I'm a bit taken back and forth here. That
commit afaics is from v3.0-rc1 and Linus iirc at least once said
something along the lines of "a regression only reported after a long
time at some point becomes just a bug". I'd say that applies there,
which is why I'm wondering if tracking this really is worth it.

Ciao, Thorsten


>>     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.
>>
>> Thanks,
>> Guenter