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    SubjectRe: [RFC PATCH] kbuild: check uniqueness of basename of modules
    On Wed, May 15, 2019 at 8:34 PM Greg KH <gregkh@linuxfoundation.org> wrote:
    >
    > On Wed, May 15, 2019 at 05:57:50PM +0900, Masahiro Yamada wrote:
    > > On Wed, May 15, 2019 at 5:14 PM Greg KH <gregkh@linuxfoundation.org> wrote:
    > > >
    > > > On Wed, May 15, 2019 at 10:08:12AM +0200, Arnd Bergmann wrote:
    > > > > On Wed, May 15, 2019 at 9:39 AM Masahiro Yamada
    > > > > <yamada.masahiro@socionext.com> wrote:
    > > > > >
    > > > > > In the recent build test of linux-next, Stephen saw a build error
    > > > > > caused by a broken .tmp_versions/*.mod file:
    > > > > >
    > > > > > https://lkml.org/lkml/2019/5/13/991
    > > > > >
    > > > > > drivers/net/phy/asix.ko and drivers/net/usb/asix.ko have the same
    > > > > > basename, and there is a race in generating .tmp_versions/asix.mod
    > > > > >
    > > > > > Kbuild has not checked this before, and it occasionally shows up with
    > > > > > obscure error message when this kind of race occurs.
    > > > > >
    > > > > > It is not trivial to catch this potential issue by eyes.
    > > > > >
    > > > > > Hence, this script.
    > > > > >
    > > > > > I compile-tested allmodconfig for the latest kernel as of writing,
    > > > > > it detected the following:
    > > > > >
    > > > > > warning: same basename '88pm800.ko' if the following are built as modules:
    > > > > > drivers/regulator/88pm800.ko
    > > > > > drivers/mfd/88pm800.ko
    > > > > > warning: same basename 'adv7511.ko' if the following are built as modules:
    > > > > > drivers/gpu/drm/bridge/adv7511/adv7511.ko
    > > > > > drivers/media/i2c/adv7511.ko
    > > > > > warning: same basename 'asix.ko' if the following are built as modules:
    > > > > > drivers/net/phy/asix.ko
    > > > > > drivers/net/usb/asix.ko
    > > > > > warning: same basename 'coda.ko' if the following are built as modules:
    > > > > > fs/coda/coda.ko
    > > > > > drivers/media/platform/coda/coda.ko
    > > > > > warning: same basename 'realtek.ko' if the following are built as modules:
    > > > > > drivers/net/phy/realtek.ko
    > > > > > drivers/net/dsa/realtek.ko
    > > > > >
    > > > > > Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
    > > > > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
    > > > >
    > > > > That looks great!
    > > > >
    > > > > > ---
    > > > > >
    > > > > > [Alternative fix ? ]
    > > > > >
    > > > > > I do not know about the user experience of modprobe etc.
    > > > > > when two different modules have the same name.
    > > > > > It does not matter if this is correctly handled by modules.order?
    > > > > >
    > > > > > If this is just a problem of the build system, it is pretty easy to fix.
    > > > > > For example, if we prepend the directory path, parallel build will
    > > > > > never write to the same file simultanously.
    > > > > >
    > > > > > asix.mod -> drivers/net/phy/asix.mod
    > > > > > asix.mod -> drivers/net/usb/asix.mod
    > > > >
    > > > > non-unique module names cause all kinds of problems, and
    > > > > modprobe can certainly not handle them correctly, and there
    > > > > are issues with symbols exported from a module when another
    > > > > one has the same name.
    > > >
    > > > /sys/modules/ will fall over when this happens as well. I thought we
    > > > had the "rule" that module names had to be unique, I guess it was only a
    > > > matter of time before they started colliding :(
    > > >
    > > > So warning is good, but forbidding this is better, as things will break.
    > > >
    > > > Or we need to fix up the places where things will break.
    > >
    > >
    > > If we intentionally break the build,
    > > we need to send fix-up patches to subsystems first.
    >
    > True, but those builds are already broken if anyone tries to use them :)
    >
    > A warning for now would be nice, that way we can find these and know to
    > fix them up over time.


    Yes, I think it is a fair point.

    Start this with warning, then people will soon notice the problem.

    Turning it into error is easy once we fix all instances.


    --
    Best Regards
    Masahiro Yamada

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