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    SubjectRe: [RFC 4/4] {RFC} kmod.c: Add new call_usermodehelper_timeout() API
    On 03/22, Boaz Harrosh wrote:
    >
    > On 03/22/2012 07:27 AM, Oleg Nesterov wrote:
    > >>
    > >> usermodehelper: implement UMH_KILLABLE
    > >>
    > >> Implement UMH_KILLABLE, should be used along with UMH_WAIT_EXEC/PROC. The
    > >> caller must ensure that subprocess_info->path/etc can not go away until
    > >> call_usermodehelper_freeinfo().
    > >> ...
    > >>
    > >> I think that my patch above does a much better/cleaner lifetime management of the
    > >> subprocess_info struct, with the use of a kref.
    > >
    > > This is subjective, you know ;) I specially tried to avoid the
    > > refcounting.
    > >
    >
    > Why?
    >
    > The all kref_ abstraction comes to a simple atomic_inc/dec.

    Again, this is subjective, but kref_ looks like the unnecessary
    complication to me. But I won't insist, see below.

    > > In any case. I do not know why do we need timeout, but this is
    > > orthogonal to KILLABLE. Please redo your patches on top of -mm
    > > tree? Please note that in this case the change becomes trivial.
    > >
    >
    > Yes you are right.

    OK, good.

    > > Hmm. For example, exit_mm() does xchg().
    > >
    >
    > Again, Personally I like xchg, but not here, not for an object
    > life-time management. Two threads share a structure, that needs
    > to go when the last one ends.

    And xchg(info->complete) implements the simplest counter,
    xchg() == NULL is equivalent to atomic_dec_and_test() == T.

    But again, again, I won't argue if you send the patch which uses
    kref_ instead. I do not maintain this code and I do not really mind.
    And I never pretended my taste is good ;)

    My point is, this is completely orthogonal to "add the timeout",
    and if you want to change the refcounting I'd suggest a separate
    patch.

    What we need is wait_for_completion_state_timeout() to avoid
    the horror like

    if (UMH_KILLABLE && !timeout)
    wait_for_completion_killable(...);
    else if (UMH_KILLABLE && timeout)
    wait_for_completion_killable_timeout(...);
    else if (!UMH_KILLABLE && !timeout)
    ...

    IOW, I think we need to export wait_for_common() first.

    This is the only complication afaics. After that "add the timeout"
    becomes almost one-liner, with or without "switch to kref_".


    > Is there an mm git tree?

    No, afaik

    > random linux-next/master point. Which should do the job.

    Yes, I think this should work.

    Oleg.



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