linux-kernel - Re: [PATCH 2/8] kill tracehook_notify

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Message-ID: <20110623132126.GA10410@redhat.com>
Date:	Thu, 23 Jun 2011 15:21:26 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	hch@...radead.org
Subject: Re: [PATCH 2/8] kill tracehook_notify_death()

Hi Tejun,

On 06/23, Tejun Heo wrote:
>
> Hello, Oleg.
>
> On Wed, Jun 22, 2011 at 11:08:34PM +0200, Oleg Nesterov wrote:
> > Kill tracehook_notify_death(), reimplement the logic in its caller,
> > exit_notify().
> >
> > This also fixes a minor bug, if the exiting task is the group_leader
> > and it is traced by its real_parent, tracehook_notify_death() returns
> > task->exit_signal or SIGCHLD depending on thread_group_empty(), this
> > looks strange.
>
> Maybe we should do the above in a separate patch?

Do you think this makes sense? OK, I can do this...

>
> > -	if (tsk->exit_signal != SIGCHLD && !task_detached(tsk) &&
> > +	if (thread_group_leader(tsk) && tsk->exit_signal != SIGCHLD &&
>
> Hmmm... it probably depends on POV but wouldn't (exit_signal != -1 &&
> exit_signal != SIGCHLD) be easier?

I disagree.

> The logic here is about demoting
> specials sigs to SIGCHLD under certain circumstances

Yes. And what is ->exit_signal? It is in fact per-process, lives in the
group_leader's task_struct. We could move it to signal_struct.

> and the check is
> there to prevent promoting -1 to SIGCHLD.

Yes, because we should never change ->exit_signal for sub-threads.

And it doesn't make sense to check exec ids (this is again per-process,
should be cleanuped) unless the task is the group leader.

> thread_group_leader() seems
> unnecessarily indirect.

This is what I disagree with. Contrary, I think thread_group_leader() exactly
explains what do we want to check. (but once again, exec_id logic should be
cleanuped, not only in this function).

Oleg.

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