Date: Mon, 14 Feb 2011 18:23:58 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: Denys Vlasenko <vda.linux@googlemail.com>,
        Roland McGrath <roland@redhat.com>, jan.kratochvil@redhat.com,
        linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
        akpm@linux-foundation.org
Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after
	PTRACE_ATTACH
Message-ID: <20110214172358.GB14528@redhat.com>
References: <20110204105343.GA12133@htj.dyndns.org> <20110207174821.GA1237@redhat.com> <20110209141803.GH3770@htj.dyndns.org> <201102132325.55353.vda.linux@googlemail.com> <20110214151340.GP18742@htj.dyndns.org> <20110214161515.GA11605@redhat.com> <20110214163346.GZ18742@htj.dyndns.org>
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On 02/14, Tejun Heo wrote:
>
> On Mon, Feb 14, 2011 at 05:15:15PM +0100, Oleg Nesterov wrote:
> > > > PTRACE_CONT in this situation would do the same.
> > >
> > > This can be fixed by updating strace, right?  strace can look at the
> > > wait(2) exit code and if the tracee stopped for group stop, wait for
> > > the tracee to be continued instead of issuing PTRACE_SYSCALL.
> >
> > Yes, in this particular case strace could be more clever.
> >
> > But. The tracee should react to SIGCONT after that, this means we
> > shouldn't "delay" this stop or force the TASK_TRACED state.
>
> Yeap, which is achievable by treating group stop differently from
> ptrace traps and make it proceed to TASK_TRACED only if ptrace wants
> to issue commands.

Yes, agreed. And this is exactly what we currently do. Except, as you
pointed out, the simple s/STOPPED/TRACED/ change is buggy. But the fix
you suggested should be almost invisible to the userland.

> (reiterating just to make sure there's no
> misunderstanding)

The same from my side ;)

Oleg.

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