linux-kernel - Re: [PATCH 0/7][v7] Container-init signal semantics

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Date:	Tue, 20 Jan 2009 23:39:27 -0500
From:	Bryan Donlan <bdonlan@...il.com>
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
Subject: Re: [PATCH 0/7][v7] Container-init signal semantics

On Sat, Jan 17, 2009 at 3:26 PM, Sukadev Bhattiprolu
<sukadev@...ux.vnet.ibm.com> wrote:
>
> Container-init must behave like global-init to processes within the
> container and hence it must be immune to unhandled fatal signals from
> within the container (i.e SIG_DFL signals that terminate the process).
>
> But the same container-init must behave like a normal process to
> processes in ancestor namespaces and so if it receives the same fatal
> signal from a process in ancestor namespace, the signal must be
> processed.
>
> Implementing these semantics requires that send_signal() determine pid
> namespace of the sender but since signals can originate from workqueues/
> interrupt-handlers, determining pid namespace of sender may not always
> be possible or safe.
>
> 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).

SIGSTOP is normally uncatchable; I note that patch 4 states that
SIGSTOP is allowed through to container-init, but given this summary
is SIGSTOP still reliable when sent to a container-init from an
ancestor namespace?
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