linux-kernel - Re: [PATCH 03/10] ptrace: implement PTRACE

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Message-ID: <20110519103412.GD627@htj.dyndns.org>
Date:	Thu, 19 May 2011 12:34:12 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	jan.kratochvil@...hat.com, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu, bdonlan@...il.com
Subject: Re: [PATCH 03/10] ptrace: implement PTRACE_SEIZE

Hello,

On Wed, May 18, 2011 at 08:17:56PM +0200, Oleg Nesterov wrote:
> On 05/16, Tejun Heo wrote:
> >
> > @@ -315,6 +338,9 @@ static int ptrace_attach(struct task_struct *task)
> >  	if (task_is_stopped(task)) {
> >  		task->jobctl |= JOBCTL_TRAP_STOP | JOBCTL_TRAPPING;
> >  		signal_wake_up(task, 1);
> > +	} else if (seize) {
> > +		task->jobctl |= JOBCTL_TRAP_STOP;
> 
> So, this can race with do_signal_stop(), it can clear TRAP_STOP and
> JOBCTL_STOP_PENDING can guarantee the tracee will trap later.

Confused.  How can do_signal_stop() clear TRAP_STOP?

> > +	 * When PT_SEIZED, it's used for both group stop and explicit
> > +	 * SEIZE/INTERRUPT traps.  Both generate PTRACE_EVENT_STOP trap
> > +	 * with accompanying siginfo.
> > +	 *
> > +	 * When !PT_SEIZED, it's used only for group stop trap with
> > +	 * CLD_STOPPED as exit_code and no siginfo.
> >  	 */
> >  	if (unlikely(current->jobctl & JOBCTL_TRAP_MASK)) {
> > -		signr = current->jobctl & JOBCTL_STOP_SIGMASK;
> > -		WARN_ON_ONCE(!signr);
> > -		ptrace_stop(signr, CLD_STOPPED, 0, NULL);
> > -		current->exit_code = 0;
> > +		if (current->ptrace & PT_SEIZED) {
> > +			ptrace_do_notify(SIGTRAP | PTRACE_EVENT_STOP << 8,
> > +					 CLD_STOPPED);
> 
> So. When PT_SEIZED, we always report PTRACE_EVENT_STOP and PTRACE_GET_SIGINFO
> always works.
> 
> Personally I agree, this looks more clean and natural.

Yeah, I like it much better.  INTERRUPT trap and group stop trap being
separate while sharing some attributes was disturbing.

Thanks.

-- 
tejun
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