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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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