linux-kernel - Re: [PATCH 03/10] ptrace: implement PTRACE

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Date:	Fri, 20 May 2011 00:42:12 +0200
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Pedro Alves <pedro@...esourcery.com>
Cc:	Tejun Heo <tj@...nel.org>, oleg@...hat.com,
	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 03/10] ptrace: implement PTRACE_SEIZE

On Thursday 19 May 2011 21:31, Pedro Alves wrote:
> On Thursday 19 May 2011 15:17:28, Tejun Heo wrote:
> > But making SEIZE not trigger INTERRUPT and SETOPTIONS without
> > requiring TRACED don't seem too difficult.  Jan, would that be enough?
> > Oleg, what do you think?
> 
> UUIC, that opens a race where between SEIZEing and
> SETOPTIONS(O_TRACE FORK|VFORK|EXEC...), the tracee can
> fork/vfork/clone/exec, without the tracer getting the
> nice corresponding PTRACE_EVENT_ events.

SEIZE,fork-in-tracee,INTERRUPT sequence is indistinguishable
from SEIZE happening two microseconds later:

fork-in-tracee,SEIZE,INTERRUPT

> In GDBs case, GDB will want to poke at memory
> right after attaching

...where "right after attaching" is defined as "when the first ptrace-stop
is reported". Which will happen very soon.

-- 
vda
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