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Re: [RFC] kern: simple futex for gnumach (version 10)

From: Richard Braun
Subject: Re: [RFC] kern: simple futex for gnumach (version 10)
Date: Tue, 7 Jan 2014 10:03:55 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

On Tue, Jan 07, 2014 at 09:29:45AM +0100, Marin Ramesa wrote:
> On 01/06/2014 03:00:35 PM, Richard Braun wrote:
> >We also need to make sure nothing bad happens to an (object, offset)
> >pair when, say, copy-on-write is performed by the VM system...
> I'll add a check_consistency() routine to futex_wake() which repeats the
> vm_map_lookup(). I'll use a sum of object address and offset for the
> event.

I'm not sure you get the point. The problem is that copy-on-write will
create shadow objects, possibly making your new lookup wrong. But
normally, such mappings are private, where a task-local address will
do the job whatever the mapping type, as long as it's valid.

> So, if the event is not the same, I'll just return from futex_wake().

> >All this looks quite tricky to me, and certainly not a "small hack
> >entry" :-/.
> I won't give up. I've spent too much time on this already. I guess
> I'll just
> have to finish it.

Hum no, this is clearly not "too much time" yet. But I understand. Just
know that we may not be able to find the time to validate and debug your
code. I'm looking at it as a reviewer only, I will miss tricky details
too, and I won't test it since I have other things on my to do list.
Same goes for practically everyone else involved in the project. Expect
to be on your own for much of the development.

Richard Braun

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