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

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Message-ID: <20110220191635.GA32682@redhat.com>
Date:	Sun, 20 Feb 2011 20:16:35 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jan Kratochvil <jan.kratochvil@...hat.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	torvalds@...ux-foundation.org, Tejun Heo <tj@...nel.org>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.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 18:06:30 +0100, Denys Vlasenko wrote:
>
> > Not exactly. Even after we fix kernel so that it properly preserves
> > group-stop across ptrace-stops, gdb will still see TWO
> > waitpid:SIGSTOP events, not one.
> >
> > First one says "the tracee has received SIGSTOP", and after PTRACE_CONT(SIGSTOP),
> > second one says "the tracee has stopped because of SIGSTOP".
> > Currently, neither strace nor gdb understands that second one
> > is different from first.
>
> I thought the kernel change being discussed should be the second SIGSTOP will
> receive the process's original parent,

No, no, the debugger should see this notification whatever we do.

> so that CTRL-Z on a debugged process
> from shell works the normal way, as without a debugger.

Yes, this is yet another problem (din't I say we have a lot of them? ;),
CTRL-Z should work and thus we have notify original parent as well.
And even this is not enough, we should change do_wait(WSTOPPED).
But this is another story, gdb shouldn't be affected by these changes.

Oleg.

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