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    SubjectRe: [RFC] [PATCH 0/2] Futex fault injection
    Ingo Molnar wrote:
    > * Peter Zijlstra <> wrote:
    >> On Tue, 2009-12-01 at 11:33 +0100, Ingo Molnar wrote:
    >>> * Sripathi Kodi <> wrote:
    >>>> Hi,
    >>>> This patch set adds fault injection for futex subsystem. It adds
    >>>> faults at places where reading/writing from user space can return
    >>>> EFAULT. This will be useful in testing any significant change to futex
    >>>> subsystem.
    >>> Instead of this unacceptably ugly and special-purpose debugfs
    >>> interface, please extend perf events to allow event injection. Some
    >>> other places in the kernel (which deal with rare events) want/need
    >>> this capability too.
    >> Thing is, he's using the 'normal' fault injection code to do this, I
    >> see no objection to doing that.
    > Yes - but its impact to the futex code is butt-ugly. That some facility
    > is in the kernel does not mean it gets a free pass to be applied
    > everywhere and anywhere.

    I don't think the "butt-ugly" argument is enough to reject the patch.
    It's a fairly subjective metric and I don't think the proposed solution
    results in "pretty" code either. In fact the super long function names
    and multi-line conditionals are arguably "ugly" (maybe not "butt-ugly"
    though). :-)

    However, the arguments are solid and I understand wanting to introduce a
    new feature in a particular way. Has there been any work done on perf
    event injection up to this point or would this be a completely new perf


    > An example of that would be tracepoints - there's no free pass to add
    > tracepoints in new places and some maintainers elect to use different
    > facilities. (or reject all current facilities)
    >> If you want to redo the fault injection subsystem, then that's another
    >> story, but then we need to convert all of its users over.
    > What i want to see is sane code in futex.c. If we add hooks/callbacks
    > i'd like it to be a complete solution helping a lot of usecases not some
    > limited approach helping testability only.
    > Thanks,
    > Ingo

    Darren Hart
    IBM Linux Technology Center
    Real-Time Linux Team

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