linux-kernel - Re: [PATCH 10/10] ptrace: implement group stop notification for ptracer

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Message-Id: <201105200048.07942.vda.linux@googlemail.com>
Date:	Fri, 20 May 2011 00:48:07 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Tejun Heo <tj@...nel.org>, jan.kratochvil@...hat.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu, bdonlan@...il.com
Subject: Re: [PATCH 10/10] ptrace: implement group stop notification for ptracer

On Thursday 19 May 2011 19:13, Oleg Nesterov wrote:
> On 05/19, Tejun Heo wrote:
> > On Thu, May 19, 2011 at 06:32:46PM +0200, Oleg Nesterov wrote:
> > > > +static void ptrace_trap_notify(struct task_struct *t)
> > > > +{
> > > > +	siginfo_t *si = t->last_siginfo;
> > > > +
> > > > +	WARN_ON_ONCE(!(t->ptrace & PT_SEIZED));
> > > > +	assert_spin_locked(&t->sighand->siglock);
> > > > +
> > > > +	/*
> > > > +	 * @t is being ptraced and new SEIZE behavior is in effect.
> > > > +	 * Schedule sticky trap which will clear on the next GETSIGINFO.
> > > > +	 */
> > > > +	t->jobctl |= JOBCTL_TRAP_NOTIFY;
> > >
> > > This is also set by do_signal_stop(). Cleared by PTRACE_GETSIGINFO.
> > >
> > > How can this work? Doesn't this mean PTRACE_GETSIGINFO becomes mandatory
> > > before PTRACE_CONT? IOW, unless the tracee does PTRACE_GETSIGINFO to clear
> > > this bit, PTRACE_CONT just leads to another trap, no?
> >
> > Yes, group stop state change raises a sticky trap condition which is
> > cleared by GETSIGINFO.
> 
> Hmm. At least now I understand the meaining what "sticky" means in
> this discussion ;) I was confused.

I still don't see why is it needed. Userspace API doesn't require it.

Are you trying to solve/simplify something on the kernel side with it?

-- 
vda
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