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From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 12 Oct 2023 14:55:04 +0200
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Subject: Re: [PATCH v7 1/5] lib/bitmap: add 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,
        Arnd Bergmann <arnd@arndb.de>
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>
> I realized that the corner case with these functions is when agnostic user
> wants to read / write > 32 bits at a time without ifdeffery applied.

Shall we change

        if (unlikely(!nbits))
                return;

to

        if (unlikely(!nbits || nbits > BITS_PER_LONG))
                return;

?

> At bare minimum this has to be documented explicitly, that callers
> may have an issue of the above calls on 32-bit platforms.

Given that bitmap_read() returns an unsigned long, and bitmap_write()
writes an unsigned long, passing a 64-bit value would be a bug.
But you are right, documenting this won't hurt.