From: Denys Vlasenko <vda.linux@googlemail.com>
To: "Indan Zupancic" <indan@nul.nu>
Cc: "Oleg Nesterov" <oleg@redhat.com>, "Tejun Heo" <tj@kernel.org>,
"Roland McGrath" <roland@redhat.com>,
jan.kratochvil@redhat.com, linux-kernel@vger.kernel.org,
torvalds@linux-foundation.org, akpm@linux-foundation.org,
"Michael Kerrisk" <mtk.manpages@googlemail.com>
Subject: Re: [RFC] Proposal for ptrace improvements
Date: Thu, 3 Mar 2011 02:30:27 +0100 [thread overview]
Message-ID: <201103030230.27363.vda.linux@googlemail.com> (raw)
In-Reply-To: <0a2c2dfb67198c5bd2cfc6e6c1896f23.squirrel@webmail.greenhost.nl>
On Thursday 03 March 2011 01:47, Indan Zupancic wrote:
> On Wed, March 2, 2011 14:32, Oleg Nesterov wrote:
> > On 03/02, Tejun Heo wrote:
> >> On Wed, Mar 02, 2011 at 06:07:35AM +0100, Indan Zupancic wrote:
> >> > I'm not sure what Denys is talking about: Currently it's impossible to
> >> > pass along SIGSTOP to traced processes. Quoting the ptrace manpage:
> >> >
> >> > PTRACE_CONT
> >> > Restarts the stopped child process. If data is nonzero and not
> >> > SIGSTOP, it is interpreted as a signal to be delivered to the
> >> > child; otherwise, no signal is delivered.
> >>
> >> AFAICS, that's not true. SIGSTOP isn't treated differently from other
> >> signals in the ptrace signal delivery path. Maybe it was true in the
> >> past.
> >
> > Yes, this is not true. And it seems this was never true.
> >
> > This is the second time this manpage confuses people in this discussion,
> > probably it should be fixed...
>
> Passing SIGSTOP does not actually stop the traced task, which is in line
> with what the manpage says. All it does is generating that second SIGSTOP
> notification, but when the task is continued it's running, not stopped.
It can be argued that after this the task is running _precisely_
because it was continued by the debugger.
> So ptraced tasks can't be stopped with SIGSTOP and continued with SIGCONT.
It can be stopped - just do not PTRACE_CONT it after second SIGSTOP
notification.
The bug is that it can't be continued with SIGCONT after that.
That's the gist of Tejun Heo's proposal.
Oleg's proposal is a bit different. It proposes that we do need
to do PTRACE_CONT after second SIGSTOP notification too,
but task will be indeed stopped after this, and resumed
when SIGCONT arrives.
--
vda
next prev parent reply other threads:[~2011-03-03 1:30 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-01 15:24 [RFC] Proposal for ptrace improvements Tejun Heo
2011-03-01 16:57 ` Denys Vlasenko
2011-03-01 17:09 ` Tejun Heo
2011-03-01 17:12 ` Tejun Heo
2011-03-01 17:21 ` Denys Vlasenko
2011-03-01 18:34 ` Tejun Heo
2011-03-01 23:51 ` Denys Vlasenko
2011-03-02 7:10 ` Tejun Heo
2011-03-02 5:07 ` Indan Zupancic
2011-03-02 7:44 ` Tejun Heo
2011-03-02 11:32 ` Indan Zupancic
2011-03-02 11:52 ` Denys Vlasenko
2011-03-02 14:50 ` Tejun Heo
2011-03-02 13:32 ` Oleg Nesterov
2011-03-03 0:47 ` Indan Zupancic
2011-03-03 1:30 ` Denys Vlasenko [this message]
2011-03-03 1:55 ` Indan Zupancic
2011-03-03 7:03 ` Tejun Heo
2011-03-01 19:06 ` Jan Kratochvil
2011-03-01 22:14 ` Denys Vlasenko
2011-03-02 7:28 ` Tejun Heo
2011-03-02 10:58 ` Denys Vlasenko
2011-03-04 16:14 ` Jan Kratochvil
2011-03-04 16:41 ` Denys Vlasenko
2011-03-04 17:07 ` Oleg Nesterov
2011-03-04 18:12 ` Jan Kratochvil
2011-03-05 8:47 ` Tejun Heo
2011-03-01 22:59 ` Denys Vlasenko
2011-03-02 7:32 ` Tejun Heo
2011-03-02 11:02 ` Denys Vlasenko
2011-03-02 11:23 ` Tejun Heo
2011-03-03 19:26 ` Oleg Nesterov
2011-03-01 23:16 ` Denys Vlasenko
2011-03-02 7:37 ` Tejun Heo
2011-03-02 11:21 ` Denys Vlasenko
2011-03-02 11:27 ` Tejun Heo
2011-03-02 11:48 ` Denys Vlasenko
2011-03-02 14:43 ` Tejun Heo
2011-03-02 15:16 ` Denys Vlasenko
2011-03-02 15:25 ` Tejun Heo
2011-03-03 17:34 ` Oleg Nesterov
2011-03-03 20:22 ` Oleg Nesterov
2011-03-04 8:23 ` Tejun Heo
2011-03-04 18:16 ` Oleg Nesterov
2011-03-05 8:33 ` Tejun Heo
2011-03-04 13:01 ` Denys Vlasenko
2011-03-04 13:41 ` Tejun Heo
2011-03-04 13:59 ` Denys Vlasenko
2011-03-04 14:07 ` Tejun Heo
2011-03-04 14:31 ` Denys Vlasenko
2011-03-04 14:40 ` Tejun Heo
2011-03-04 17:05 ` Denys Vlasenko
2011-03-04 17:12 ` Linus Torvalds
2011-03-04 18:59 ` Denys Vlasenko
2011-03-04 19:24 ` Linus Torvalds
2011-03-04 16:13 ` Oleg Nesterov
2011-03-04 16:30 ` Oleg Nesterov
2011-03-04 8:44 ` Tejun Heo
2011-03-04 16:01 ` Oleg Nesterov
2011-03-04 16:15 ` Tejun Heo
2011-03-04 16:26 ` Oleg Nesterov
2011-03-07 15:08 ` PTRACE_SEIZE/INTERRUPT: " Oleg Nesterov
2011-03-09 9:41 ` Tejun Heo
2011-03-09 17:30 ` Oleg Nesterov
2011-03-07 20:43 ` Roland McGrath
2011-03-09 10:28 ` Tejun Heo
2011-03-10 18:33 ` Steven Rostedt
2011-03-11 8:13 ` Tejun Heo
2011-03-11 8:22 ` Ingo Molnar
2011-03-11 9:35 ` Srikar Dronamraju
2011-03-11 9:43 ` Ingo Molnar
2011-03-14 1:03 ` Frank Ch. Eigler
2011-03-10 15:55 ` Steven Rostedt
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