Re: [PATCH] New System call unshare (try 2)

[Janak Desai <janak@us.ibm.com>]

Chris Wright wrote:
> * Jamie Lokier (jamie@shareable.org) wrote:
>
> > Janak Desai wrote:
> >
> > > 	Don't allow sighand unsharing if not unsharing vm
> >
> > Why not?  It's permitted to clone with unshared sighand and shared vm,
> > and it's useful too.
>
>
> I think that one's just backwards.  Although I do question how useful it
> is to unshare sighand.  Sharing vm is pretty intimate ;-)
>
>
> > It's the combination shared sighand + unshared vm which is not
> > allowed by clone - so I think that's what you should refuse.
> >
> >
> > > 	Don't allow vm unsharing if task cloned with CLONE_THREAD
> >
> > It would be better to do what clone does, and say "don't allow sighand
> > unsharing if task cloned with CLONE_THREAD".  This is because
> > CLONE_THREAD tasks must have shared signals.
>
>
> Yes, I agree.
>
>
> > In combination with the rule above for sighand (my rule, not yours),
> > that implies "don't allow vm unsharing.." as a consequence.
> >
> >
> > > 	Don't allow vm unsharing if the task is performing async io
> >
> > Why not?
> >
> > Async ios are tied to an mm (see lookup_ioctx in fs/aio.c), which may
> > be shared among tasks.  I see no reason why the async ios can't
> > continue and be waited in on in other tasks that may be using the old mm.
>
>
> My concern was the case where there are no other tasks.  But I don't
> think that's an issue other than having the aio effect of setting up
> aio then exiting.
>
> thanks,
> -chris
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Thanks Chris and Jamie. I understand the issues that you raised and
agree with your change recommendations. I will make the necessary
changes, test aio and unsharing of signal handlers (while keeping
shared vm) and post the updated patch by tomorrow.

-Janak

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