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    SubjectRe: [PATCH 1/2] Add thread_info_cache_init() to all archs
    On Mon, 14 Apr 2008 10:38:26 +1000 Benjamin Herrenschmidt <benh@ozlabs.org> wrote:

    > > > +#ifndef thread_info_cache_init
    > > > +#define thread_info_cache_init do { } while(0)
    > > > +#endif
    > >
    > > This trick does cause a bit of a problem: it is undefined which arch header
    > > file is to provide the alternative definition of thread_info_cache_init.
    >
    > I this case it's well defined: thread_info.h. Maybe I should add a
    > comment ?
    >
    > > So we can (and have) ended up in the situation where the override appears
    > > in different files on different architectures and various screwups ensue.
    >
    > Yup.
    >
    > > So I'd suggest that we have a bigfatcomment telling implementors which file
    > > the override should be implemented in. And make sure that this arch file is
    > > directly included from within sched.h.
    >
    > Will do.
    >
    > > I have a suspicion that we can still get in a mess if .c files include the
    > > per-arch file and don't include sched.h, but I forget where this happened
    > > and why it broke stuff.
    >
    > In this case, there's only one call site and will only every be one, so
    > that shouldn't be a problem. I don't see init/main.c not including
    > sched.h

    As long as init.c directly includes sched.h, and as long as sched.h
    directly includes thread_info.h and as long as all architectures which
    provide the override put it in their thread_info.h, and as long as the same
    applies to all future .c users, we're good. That's a lot of "as long as"'s ;)

    > > Sigh. A nice, coded-in-C implementation within each and every architecture
    > > remains the best implementation, and all the little tricks-to-save-typing
    > > have failure modes.
    >
    > Well, I started doing it in all arch, and people around here told me
    > that was not a good idea , that it would be trouble if the prototype
    > ever had to change (adding an arg, etc... though very unlikely to happen
    > in that case, granted).

    Bah. Use of grep and basic typing skills: not so hard.

    > > otoh, if only one .c file will ever call this function then I think that
    > > all problems are solved by
    > >
    > > a) moving the above ifdeffery into the .c file
    > > b) adding a comment explaining which arch file must provide the override
    > > c) directly including that file from within the .c file.
    >
    > I can definitely do that. I have no problem either way. I can add to all
    > archs too, it's just that whatever way I choose, some people won't be
    > happy with it :-)
    >
    > Anyway, I'll move the ifdeferry to init/main.c then.

    Thanks ;)

    I'm still wounded by my recent encounter with set_softirq_pending()
    and or_softirq_pending().


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