linux-kernel - Re: [RFC][PATCH 0/6][v3] Container-init signal semantics

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Date:	Mon, 22 Dec 2008 16:27:32 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	oleg@...hat.com, roland@...hat.com, bastian@...di.eu.org,
	daniel@...ac.com, xemul@...nvz.org, containers@...ts.osdl.org,
	linux-kernel@...r.kernel.org, sukadev@...ibm.com
Subject: Re: [RFC][PATCH 0/6][v3] Container-init signal semantics

Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com> writes:

> Eric W. Biederman [ebiederm@...ssion.com] wrote:
>
> | 
> | - container-init is responsible for setting the rest of the signals
> |   to SIG_IGN.
>
> Oleg pointed out that we could drop SIG_DFL signals to global init early
> to ensure wait_for_completion_killable/lock_page_killable don't incorrectly
> believe that a fatal signal is pending. (patch 2/6).
>
> If that patch is valid regardless of containers, it would be a minor
> extension to get container-inits to drop SIG_DFL signals too, right ?

Yes.

> So the bigger problem/unknown for me is the sig_from_user() in patch 4/6
> (i.e determining if it safe to deref the pid-ns of sender). We went from
> !in_interrupt() to the SIG_FROM_USER flag to this.
>
> If that is correct, I am hoping it would come down to opitmizing the code
> if possible (eg: can/should we avoid passing same_ns into sig_ignored()
>
> There is probably some ugliness :-) but do you see any other correctness 
> issues ?

I haven't dug in too deep but right now my concern are user space semantics,
I don't want to wind up with something ugly there because we can not change
it later.

So if we can write a description of what happens to signals to cinit
that is right 100% of the time.  Something we can write a test case
for that tests all of the corner cases and it always get the same
results. I am happy.

I don't mind dropping signals early as an optimization, but if it
is just an optimization we can't count on it in cinit.

So I would rather deliver less and make user space deal with it,
then deliver more cause problems for user space.

Eric
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