linux-kernel - Re: [PATCH 06/11] ptrace: make group stop state visible via PTRACE

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Message-ID: <20110510171106.GA32637@redhat.com>
Date:	Tue, 10 May 2011 19:11:06 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	jan.kratochvil@...hat.com, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu,
	Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Kyle McMartin <kyle@...artin.ca>, Helge Deller <deller@....de>,
	"James E.J. Bottomley" <jejb@...isc-linux.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Chris Metcalf <cmetcalf@...era.com>, x86@...nel.org
Subject: Re: [PATCH 06/11] ptrace: make group stop state visible via
	PTRACE_GETSIGINFO

On 05/10, Oleg Nesterov wrote:
>
> > @@ -540,6 +542,17 @@ static int ptrace_getsiginfo(struct task_struct *child, siginfo_t *info)
> >
> >  	error = 0;
> >  	*info = *child->last_siginfo;
> > +
> > +	/*
> > +	 * If reporting ptrace trap for a seized tracee, enable reporting
> > +	 * of info->si_pt_flags.
> > +	 */
> > +	if ((child->ptrace & PT_SEIZED) &&
> > +	    (info->si_code & (0x7f | ~0xffff)) == (__SI_TRAP | SIGTRAP)) {
>
> Can't we simply check (from->si_code & __SI_MASK) == __SI_TRAP ?
>
> > +		/* report whether group stop is in effect w/ SI_STOPPED */
> > +		if (sig->group_stop_count || (sig->flags & SIGNAL_STOP_STOPPED))
>
> We have more and more "group_stop_count || SIGNAL_STOP_STOPPED" checks,
> perhaps we should make a helper. Or at least invent the short name to
> denote the group-stopped-or-in-progress to simplify the discussions ;)
>
>
> Still, this is strange. With this change ptrace_getsiginfo() reports
> the extra "volatile" info which wasn't reported by the tracee itself.
> If the tracer does PTRACE_SETSIGINFO twice in a row, it can see the
                     ^^^^^^^^^^^^^^^^^
                     PTRACE_GETSIGINFO
> different si_pt_flags's.

Forgot to mention... Probably we can ignore this but the tracer can
set/clear __SI_TRAP via PTRACE_SETSIGINFO, after that PTRACE_GETSIGINFO
changes its behaviour.

Oleg.

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