Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.36 as permitted sender) client-ip=23.128.96.36;
MIME-Version: 1.0
References: <20230922080848.1261487-1-glider@google.com> <20230922080848.1261487-3-glider@google.com>
 <CAG_fn=UeFoyhZvPJ7pGPrc5011D9h1e4ioffat4eUfVHP6Hd-Q@mail.gmail.com> <ZRF7r0ZjxcL9C8U8@smile.fi.intel.com>
In-Reply-To: <ZRF7r0ZjxcL9C8U8@smile.fi.intel.com>
From:   Alexander Potapenko <glider@google.com>
Date:   Mon, 25 Sep 2023 15:09:04 +0200
Message-ID: <CAG_fn=V8Mx89dOfKf88nEq9V9i_kMYaOdGjd3DQVOWnYrandyA@mail.gmail.com>
Subject: Re: [PATCH v5 2/5] lib/test_bitmap: add tests for bitmap_{read,write}()
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     catalin.marinas@arm.com, will@kernel.org, pcc@google.com,
        andreyknvl@gmail.com, linux@rasmusvillemoes.dk,
        yury.norov@gmail.com, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, eugenis@google.com,
        syednwaris@gmail.com, william.gray@linaro.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, Sep 25, 2023 at 2:23=E2=80=AFPM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Mon, Sep 25, 2023 at 02:16:37PM +0200, Alexander Potapenko wrote:
>
> ...
>
> > > +/*
> > > + * Test bitmap should be big enough to include the cases when start =
is not in
> > > + * the first word, and start+nbits lands in the following word.
> > > + */
> > > +#define TEST_BIT_LEN (1000)
> >
> > Dunno why this didn't fire previously, but CONFIG_CPU_BIG_ENDIAN=3Dy
> > kernel reports mismatches here, presumably because the last quad word
> > ends up partially initialized.
>
> Hmm... But if designed and used correctly it shouldn't be the issue,
> and 1000, I believe, is carefully chosen to be specifically not dividable
> by pow-of-2 value.
>

The problem manifests already right after initialization:

static void __init test_bit_len_1000(void)
{
        DECLARE_BITMAP(bitmap, TEST_BIT_LEN);
        DECLARE_BITMAP(exp_bitmap, TEST_BIT_LEN);
        memset(bitmap, 0x00, TEST_BYTE_LEN);
        memset(exp_bitmap, 0x00, TEST_BYTE_LEN);
        expect_eq_bitmap(exp_bitmap, bitmap, TEST_BIT_LEN);
}

...
[   29.601614][    T1] test_bitmap: [lib/test_bitmap.c:1250] bitmaps
contents differ: expected
"960-963,966-967,969,971-973,976,978-979,981", got "963"
...

So it's probably expect_eq_bitmap() that is incorrectly rounding up
the bitmap length somewhere (or maybe it is not supposed to be used
for non-aligned bitmaps?)
Looking further...