linux-kernel - Re: [PATCH v3] Make PTRACE_SEIZE set ptrace options specified in 'data'

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Date:	Fri, 09 Sep 2011 14:28:55 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Pedro Alves <pedro@...esourcery.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org,
	Denys Vlasenko <vda.linux@...glemail.com>
Subject: Re: [PATCH v3] Make PTRACE_SEIZE set ptrace options specified in
 'data'

On Fri, 2011-09-09 at 12:12 +0100, Pedro Alves wrote:
> On Thursday 08 September 2011 19:22:04, Denys Vlasenko wrote:
> > Make PTRACE_SEIZE set ptrace options specified in 'data' parameter
> >     
> > This can be used to close a few corner cases in strace where we get
> > unwanted racy behavior after attach, but before we have a chance
> > to set options (the notorious post-execve SIGTRAP comes to mind),
> 
> I'm still confused on why you're raising the SIGTRAP argument.  Did you see
> 
>  https://lkml.org/lkml/2011/9/8/7
> 
> From previous discussions, I understood that PTRACE_SEIZE _always_
> disables
> the post-execve SIGTRAP, so I don't believe that race actually exists.
> Or is that not the case?


I believe it is not the case. And I object to making it the case.
My sense of taste says the approach "you need to use SEIZE to affect
feature <foo>" for various unrelated <foo> makes ptrace API ugly.
Especially that in this case, we already have a method in API
to suppress post-execve SIGTRAP.

-- 
vda


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