linux-kernel - Re: [PATCH 1/2] signals: kill(-1) should only signal processes in the same namespace

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Date:	Thu, 17 Jul 2008 21:32:54 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Pavel Emelyanov <xemul@...nvz.org>
Cc:	Daniel Hokka Zakrisson <daniel@...ac.com>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, ebiederm@...ssion.com,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/2] signals: kill(-1) should only signal processes in the same namespace

On 07/17, Pavel Emelyanov wrote:
>
> Daniel Hokka Zakrisson wrote:
> > 
> > The way zap_pid_ns_processes does it is worse, since it signals every
> > thread in the namespace rather than every thread group. So either we walk
> 
> It's questionable whether there are more "threads in a pid namespace" than
> "processes in a system".
> 
> E.g. on my notebook there are ~110 processes and ~150 threads. So having 
> this setup launched in 10 containers you'll have to walk 1100 tasks, while
> zap_pid_ns_processes only 150 ;)
> 
> Some real-life example with containers: on one of our servers with 10 
> containers serving as git repo, bulding system and some other stuff there 
> are ~200 process totally and ~20 threads in each container. See?
> 
> I tend to believe that walking threads in a container is cheaper then
> walking processes in a system...

kill_something_info() can't walk threads, think about the realtime signals.

Anyway, I think we should change kill_something_info(-1) to use rcu_read_lock()
instead of tasklist.

Oleg.

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