linux-kernel - Re: Signals to cinit

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Date:	Mon, 10 Nov 2008 18:24:05 -0800
From:	sukadev@...ux.vnet.ibm.com
To:	Oleg Nesterov <oleg@...hat.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

Oleg Nesterov [oleg@...hat.com] wrote:
| (lkml cced because containers list's archive is not useable)
| 
| On 11/10, Oleg Nesterov wrote:
| >
| > On 11/01, sukadev@...ux.vnet.ibm.com wrote:
| > >
| > > Other approaches to try ?
| >
| > I think we should try to do something simple, even if not perfect. Because
| > most users do not care about this problem since they do not use containers
| > at all. It would be very sad to add intrusive changes to the code.
| >
| > I think we should fix another problem first. send_signal()->copy_siginfo()
| > path must be changed anyway, when the signal comes from the parent ns we
| > report the "wrong" si_code/si_pid, yes? So, somehow send_signal() must
| > have "bool from_parent_ns" (or whatever) annyway.

Yes, this was in both the patchsets we reviewed last year :-) I can send
this fix out independently.

| >
| > Now, let's forget forget for a moment that send_signal()->__sigqueue_alloc()
| > can fail.
| >
| > I think we should encode this "from_parent_ns" into "struct siginfo". I do
| > not think it is good idea to extend this structure, I think we can introduce
| > SI_FROM_PARENT_NS or we perhaps can use "SI_FROMUSER(info) && info->si_pid == 0".
| > Or something. yes, sys_rt_sigqueueinfo() is problematic...

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 ?

Of course, this is a new scenario, specific to containers, and we may be
able to define the policy without changing semantics.
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