linux-kernel - Re: [PATCH 3/5] lib/bitmap: add test for bitmap_{from,to}

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Date:   Mon, 27 Feb 2023 06:59:12 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>,
        Yury Norov <yury.norov@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 3/5] lib/bitmap: add test for bitmap_{from,to}_arr64

On 2/27/23 06:46, Alexander Lobakin wrote:
> From: Yury Norov <yury.norov@...il.com>
> Date: Sat, 25 Feb 2023 16:06:45 -0800
> 
>> On Sat, Feb 25, 2023 at 04:05:02PM -0800, Yury Norov wrote:
>>> On Sat, Feb 25, 2023 at 10:47:02AM -0800, Guenter Roeck wrote:
>>>> Hi,
>>>>
>>>> On Thu, Apr 28, 2022 at 01:51:14PM -0700, Yury Norov wrote:
>>>>> Test newly added bitmap_{from,to}_arr64() functions similarly to
>>>>> already existing bitmap_{from,to}_arr32() tests.
>>>>>
>>>>> Signed-off-by: Yury Norov <yury.norov@...il.com>
>>>>
>>>> Ever since this test is in the tree, several of my boot tests show
>>>> lots of messages such as
>>>>
>>>> test_bitmap: bitmap_to_arr64(nbits == 1): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000001)
> 
> Hmmm, the whole 4 bytes weren't touched.
> 
>>>> test_bitmap: bitmap_to_arr64(nbits == 2): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000003)
>>>> test_bitmap: bitmap_to_arr64(nbits == 3): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000007)
> 
> This is where it gets worse...
> 
>>>> ...
>>>> test_bitmap: bitmap_to_arr64(nbits == 927): tail is not safely cleared: 0xa5a5a5a500000000 (must be 0x000000007fffffff)
>>>> test_bitmap: bitmap_to_arr64(nbits == 928): tail is not safely cleared: 0xa5a5a5a580000000 (must be 0x00000000ffffffff)
> 
> I don't see the pattern how the actual result gets generated. But the
> problem is in the bitmap code rather than in the subtest -- "must be"s
> are fully correct.
> 
> Given that the 0xa5s are present in the upper 32 bits, it is Big Endian
> I guess? Maybe even 32-bit Big Endian? Otherwise I'd start concerning
> how comes it doesn't reproduce on x86_64s :D
> 

It does reproduce on 32-bit x86 builds, and as far as I can see
it is only seen with 32-bit little endian systems.

Guenter

>>>
>>> This may be a real problem. Can you share what's the system is? What's
>>> endianness and register length?
>>>
>>> + Alexander Lobakin, the author of the exact subtest.
>>
>> Forgot to add
> 
> Oh, thanks for letting me know!
> 
>>    
>>>> but then:
>>>>
>>>> test_bitmap: all 6550 tests passed
>>>
>>> It's because corresponding error path doesn't increment failed_tests
>>> counter. I'll send a fix shortly.
> 
> [...]
> 
> Thanks,
> Olek