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From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 12 Oct 2023 15:22:28 +0200
Message-ID: <CAG_fn=W_7nqtKZdDOfjYT51+T-iqAyrmEHrH9O45k1OH8g_NKA@mail.gmail.com>
Subject: Re: [PATCH v7 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, aleksander.lobakin@intel.com,
        linux@rasmusvillemoes.dk, yury.norov@gmail.com,
        alexandru.elisei@arm.com, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, eugenis@google.com,
        syednwaris@gmail.com, william.gray@linaro.org
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On Wed, Oct 11, 2023 at 8:03=E2=80=AFPM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> On Wed, Oct 11, 2023 at 07:28:32PM +0200, Alexander Potapenko wrote:
> > Add basic tests ensuring that values can be added at arbitrary position=
s
> > of the bitmap, including those spanning into the adjacent unsigned
> > longs.
>
> Would be nice to have an additional test like
>
>         bitmap_write(..., 33 /* or anything > 32 */);
>
> This will require ifdeffery. So at least this code may warn users about c=
orner
> cases in the agnostic code.

We could go with bitmap_write(..., BITS_PER_LONG + 1):

        /*
         * Setting/getting more than BITS_PER_LONG bits should not crash th=
e
         * kernel. READ_ONCE() prevents constant folding.
         */
        bitmap_write(NULL, 0, 0, READ_ONCE(bits_per_long) + 1);
        /* Return value of bitmap_read() is undefined here. */
        bitmap_read(NULL, 0, READ_ONCE(bits_per_long) + 1);

I'll add the above code in v8 (sometime next week, hope to receive
some comments from the ARM folks).