linux-kernel - Re: [PATCH 4/5] ptrace: implement TRAP_NOTIFY and use it for group stop events

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Date:	Fri, 17 Jun 2011 17:12:36 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	vda.linux@...glemail.com, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu, bdonlan@...il.com,
	pedro@...esourcery.com
Subject: Re: [PATCH 4/5] ptrace: implement TRAP_NOTIFY and use it for group
 stop events

Hello, Oleg.

On Thu, Jun 16, 2011 at 09:51:38PM +0200, Oleg Nesterov wrote:
> I already applied this series. But somehow I have the fuzzy feeling we
> can simplify JOBCTL_TRAP_NOTIFY/JOBCTL_TRAP_STOP logic later. No, I can't
> explain what I mean ;)

Heh, yeah, please go ahead.

> One question,
> 
> > @@ -1797,8 +1824,10 @@ static void ptrace_stop(int exit_code, int why, int clear_code, siginfo_t *info)
> >  	if (why == CLD_STOPPED && (current->jobctl & JOBCTL_STOP_PENDING))
> >  		gstop_done = task_participate_group_stop(current);
> >
> > -	/* any trap clears pending STOP trap */
> > +	/* any trap clears pending STOP trap, STOP trap clears NOTIFY */
> >  	task_clear_jobctl_pending(current, JOBCTL_TRAP_STOP);
> > +	if (info && info->si_code >> 8 == PTRACE_EVENT_STOP)
> > +		task_clear_jobctl_pending(current, JOBCTL_TRAP_NOTIFY);
> 
> OK, but can't we check why == CLD_STOPPED instead of PTRACE_EVENT_STOP?

Yeap, sure.  The reason why I used PTRACE_EVENT_STOP was because
PTRACE_LISTEN needs the same test and it doesn't have access to @why.
Maybe it's better to create ptrace_is_trap_stop(si)?

> In fact, can't we move all code above under 'if (why == CLD_STOPPED)' ?
> JOBCTL_TRAP_STOP can't be set otherwise, no? I am almost sure I missed
> something though.

JOBCTL_TRAP_STOP should also be cleared on CLD_TRAPPED traps.  ie. If
the ptracer does PTRACE_INTERRUPT and then wait(2) reports
PTRACE_EVENT_FORK, there won't be another PTRACE_EVENT_STOP.

Thanks.

-- 
tejun
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