linux-kernel - Re: + proc-connector-add-event-for-process-becoming-session-leader.patch added to -mm tree

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Date:	Wed, 24 Jun 2009 16:44:46 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Scott James Remnant <scott@...ntu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Helsley <matthltc@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: +
	proc-connector-add-event-for-process-becoming-session-leader.patch
	added to -mm tree

On 06/24, Scott James Remnant wrote:
>
> On Tue, 2009-06-23 at 22:29 +0200, Oleg Nesterov wrote:
>
> > > The act of a process becoming a session leader is a useful signal to a
> > > supervising init daemon such as Upstart.
> > ...
> > > @@ -360,8 +360,10 @@ void __set_special_pids(struct pid *pid)
> > >  {
> > >  	struct task_struct *curr = current->group_leader;
> > >
> > > -	if (task_session(curr) != pid)
> > > +	if (task_session(curr) != pid) {
> > >  		change_pid(curr, PIDTYPE_SID, pid);
> > > +		proc_sid_connector(curr);
> > > +	}
> >
> > Wouldn't it better to change sys_setsid() then? This looks more clear
> > imho, and we can move proc_sid_connector() outside of tasklist_lock.
> >
> > Note also that __set_special_pids() does not neccessary mean we are
> > becoming a session leader, see daemonize().
> >
> Actually, I specifically wanted to receive this event if the process
> called daemonize() which is why this is done here rather than in
> sys_setsid()

Aha. I was confused by "becoming a session leader" in the changelog.

> The new session is important information to init in figuring out what
> the process is up to (ie, fork(), setsid(), fork() = daemonise)

daemonize() is only needed when a user-space thread does kernel_thread(),
hopefully it will die eventually, this is already deprecated. Then we can
move proc_sid_connector() to sys_setsid(), I think.

Thanks!

Oleg.

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