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

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Message-ID: <20110217193324.GA13661@redhat.com>
Date:	Thu, 17 Feb 2011 20:33:24 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Jan Kratochvil <jan.kratochvil@...hat.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Tejun Heo <tj@...nel.org>, 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 02/17, Roland McGrath wrote:
>
> > OK... Yes, perhaps PTRACE_{DETACH,CONT}(SIGCONT) should override
> > SIGNAL_STOP_STOPPED too. This makes sense, and this connects to
> > the problem with SIGNAL_STOP_DEQUEUED I mentioned above.
>
> It's not at all clear this really does make sense.

Yes, I already changed my mind, see another email from me ;)

> I think this may
> reflect a (common) misunderstanding of what the SIGCONT semantics are
> (aside from ptrace).  Resuming the process is not the action of
> delivering SIGCONT.

Yes. I was confused by "for a naive/legacy debugger", somehow I missed
this doesn't work with the current code anyway, no need to add this
feature.

> So IMHO what makes most sense given what all the normal semantics are
> is that PTRACE_CONT,SIGCONT does nothing magical, and generating a
> fresh SIGCONT (i.e. kill) is the way you resume from job control stop.

Exactly.

All other things we discussed are "small details". This is the most
noticeable change.

Oleg.

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