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

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Message-ID: <20110221142325.GA16664@redhat.com>
Date:	Mon, 21 Feb 2011 15:23:25 +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 02/20, Jan Kratochvil wrote:
>
> On Sun, 20 Feb 2011 21:38:19 +0100, Oleg Nesterov wrote:
>
> > So. So far I assume you are not against this change ;)
>
> No, although you should provide the patch in advance, it would be nice to also
> post it first to <gdb@...rceware.org> for comments.

OK.

> Now if new GDB should allow inferior functions calls on previously
> `(T) stopped' process doing PTRACE_CONT(SIGCONT)

No, no, this won't work. You need to send SIGCONT via kill/tkill. Once
again, we can add the special case for PTRACE_CONT(SIGCONT), but please
look at Roland's comment: http://marc.info/?l=linux-kernel&m=129796917823181

And given that currently gdb does PTRACE_CONT(0) this special case can't
help anyway unless you change gdb.

> but how to make it `(T) stopped' afterwards?  PTRACE_CONT(SIGSTOP)
> right after the inferior call will make the old kernels run the inferior - we
> do not want that.

Hmm... probably I am totally confused... but PTRACE_CONT(SIGSTOP)
should work in this case, the tracee reports SIGTRAP after the single-step
(if I understand correctly how gdb implements this).

Oleg.

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