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

[Tejun Heo <tj@kernel.org>]

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