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Message-ID: <20091201125537.GA23382@elte.hu>
Date: Tue, 1 Dec 2009 13:55:37 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Sripathi Kodi <sripathik@...ibm.com>,
Fr??d??ric Weisbecker <fweisbec@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
linux-kernel@...r.kernel.org, Darren Hart <dvhltc@...ibm.com>
Subject: Re: [RFC] [PATCH 0/2] Futex fault injection
* Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2009-12-01 at 11:33 +0100, Ingo Molnar wrote:
> > * Sripathi Kodi <sripathik@...ibm.com> 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.
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
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