linux-kernel - Re: Signals to cinit

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Message-ID: <20081114172633.GA10508@redhat.com>
Date:	Fri, 14 Nov 2008 18:26:33 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Pavel Emelyanov <xemul@...nvz.org>, daniel@...ac.com,
	Nadia Derbey <Nadia.Derbey@...l.net>, serue@...ibm.com,
	clg@...ibm.com, Containers <containers@...ts.osdl.org>,
	sukadev@...ibm.com, linux-kernel@...r.kernel.org
Subject: Re: Signals to cinit

On 11/12, Sukadev Bhattiprolu wrote:
>
> Oleg Nesterov [oleg@...hat.com] wrote:
>
> | On 11/10, sukadev@...ux.vnet.ibm.com wrote:
> | >
> | > Also, what happens if a fatal signal is first received from a descendant
> | > and while that is still pending, the same signal is received from ancestor
> | > ns ?  Won't the second one be ignored by legacy_queue() for the non-rt case ?
>
> On second thoughts, cinit is a normal process in its ancestor ns so it
> might very well ignore the second instance of the signal (as long as it
> does not ignore SIGKILL/SIGSTOP)
>
> |
> | Please see my another email:
> |
> | 	We must also change sig_ignored() to drop SIGKILL/SIGSTOP early when
> | 	it comes from the same ns. Otherwise, it can mask the next SIGKILL
> | 	from the parent ns.
>
> Ok.
>
> |
> | 	But this perhaps makes sense anyway, even without containers.
> | 	Currently, when the global init has the pending SIGKILL, we can't
> | 	trust __wait_event_killable/etc, and this is actually wrong.
> |
> | We can drop other SIG_DFL signals from the same namespace early as well.
>
> I think Eric's patchset did this and iirc, we ran into the problem of
> blocked SIG_DFL signals ?

Yes sure, I meant unblocked SIG_DFL signals. But SIGKILL can't be
blocked fortunately.

Again, the parent ns can't rely on, say, SIGTERM. It can be missed
if cinit has a handler, we can do nothing in this case. And if it
is blocked, most probably cinit already has a handler, or it will
set it later, say, after exec. Or it can be just ignored.

> | Or, we can just ignore this (imho) minor problem.
>
> I think so too.

Great, so perhaps we can ignore the problem for now, and fix it
later if the need arises.

Oleg.

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