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    SubjectRe: [Patch v4 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs
    On Tue, Oct 22, 2019 at 09:53:06PM +0200, Rikard Falkeborn wrote:
    > On Fri, Oct 11, 2019 at 07:27:37PM -0700, Andrew Morton wrote:
    > > On Wed, 9 Oct 2019 23:45:02 +0200 Rikard Falkeborn <rikard.falkeborn@gmail.com> wrote:
    > >
    > > > GENMASK() and GENMASK_ULL() are supposed to be called with the high bit
    > > > as the first argument and the low bit as the second argument. Mixing
    > > > them will return a mask with zero bits set.
    > > >
    > >
    > > I'm seeing some breakage in code which is newly added in linux-next:
    > >
    >
    > As of next-20191021, those breakages are fixed ([0], [1]). next-20191021
    > now builds (at least for x86-64) with the GENMASK compile checks added.
    >
    > I also stumbled upon [2], which is a fix for an unused macro in a header
    > in mips/include/asm. next-201008 contained both v3 of this patch and the
    > mips header with the bad GENMASK in without build regressions, so it
    > *should* be ok to include v4 (but given the track record of this patch,
    > I totally understand if you want to wait until [2] lands in mips-next and
    > linux-next).
    >
    > Rikard
    >
    > [0]: https://lore.kernel.org/patchwork/patch/1139777/
    > [1]: https://lore.kernel.org/patchwork/patch/1139778/
    > [2]: https://lore.kernel.org/linux-mips/20191022192547.480095-1-rikard.falkeborn@gmail.com/T/#u

    And as of next-20191031, the mentioned mips-header is fixed [0]. Also, a
    recently introduced arm-bug has also been fixed. I just built x86-64 and
    arm64 allmodconfigs without issue.

    Trying to get this patch merged feels a bit like playing whack a-mole.
    Perhaps it would have been better to make it a warning at first, and
    then promote the warning to an error in a later release? Then everyone
    would have the warning in their tree when they do development and the
    number if issues in next would be (almost) zero.

    Rikard

    [0]: https://lore.kernel.org/linux-mips/20191009013721.qda2bo5teppr7nom@pburton-laptop/T/#m6e7cd9c89ef06240fe3cd36a60bd73eff1a1ea5d
    [1]: https://www.spinics.net/lists/arm-kernel/msg764473.html

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