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

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Date:   Mon, 27 Feb 2023 15:46:54 +0100
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Yury Norov <yury.norov@...il.com>,
        Guenter Roeck <linux@...ck-us.net>
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

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

>>
>> 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