linux-kernel - Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after PTRACE

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Message-ID: <20110219201603.GB8662@redhat.com>
Date:	Sat, 19 Feb 2011 21:16:03 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jan Kratochvil <jan.kratochvil@...hat.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Tejun Heo <tj@...nel.org>, Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 1/1] ptrace: make sure do_wait() won't hang after
	PTRACE_ATTACH

On 02/18, Jan Kratochvil wrote:
>
> On Thu, 17 Feb 2011 20:19:52 +0100, Oleg Nesterov wrote:
> > > > That is after PTRACE_DETACH(0) the process should remain `T (stopped)'
> > > > iff the process was `T (stopped)' before PTRACE_ATTACH.
> > > >  - PTRACE_DETACH(0)       should preserve `T (stopped)'.
> > >
> > > I assume you are thinking about PTRACE_ATTACH + wait():SIGSTOP
> > > + PTRACE_DETACH(0) sequence.
> >
> > plus it should be stopped before attach, I assume. Otherwise this
> > not true with the current code.
>
> I did not talk about the current code.  I was making a proposal of new
> behavior (which should not break existing software).

Confused.

> If PTRACE_ATTACH was done on process with `T (stopped)'

this matters "it should be stopped before attach"

> then after
> PTRACE_DETACH(0) again the process should be `T (stopped)'.

Regardless of what the debugger did in between? This can't be right.
I'd say, it doesn't make sense to take the state of the tracee before
PTRACE_ATTACH into account. What does matter, is its state before
PTRACE_DETACH.

If the debugger did not resume the tracee before PTRACE_DETACH, then
of course I agree, PTRACE_DETACH(0) should preserve T (stopped).

But again, lets discuss this separately.

Oleg.

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