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

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Date:	Mon, 22 Dec 2008 02:55:48 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	oleg@...hat.com, ebiederm@...ssion.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:

> This patchset implements the design/simplified semantics suggested by
> Oleg Nesterov.  The simplified semantics for container-init are:
>
> 	- container-init must never be terminated by a signal from a
> 	  descendant process.
>
> 	- container-init must never be immune to SIGKILL from an ancestor
> 	  namespace (so a process in parent namespace must always be able
> 	  to terminate a descendant container).
>
> 	- container-init may be immune to unhandled fatal signals (like
> 	  SIGUSR1) even if they are from ancestor namespace (SIGKILL is
> 	  the only reliable signal from ancestor namespace).

It sounds you are still struggling to get something that works and gets
done what needs to be done.  So let me suggest a simplified semantic that
should be easier to implement and test, and solves the biggest problem
that we must solve in the kernel.

- container-init ignores SIGKILL and SIGSTOP.

- container-init is responsible for setting the rest of the signals
  to SIG_IGN.

If that isn't enough for all of the init's we can go back and
solve more in kernel land.  That simplified semantic is certainly
enough for sysvinit.

> Limitations/side-effects of current design
>
> 	- Container-init is immune to suicide - kill(getpid(), SIGKILL) is
> 	  ignored. Use exit() :-)

That sounds like correct behavior.

Eric
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