From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758917Ab1IINPl (ORCPT ); Fri, 9 Sep 2011 09:15:41 -0400 Received: from relay1.mentorg.com ([192.94.38.131]:55992 "EHLO relay1.mentorg.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758899Ab1IINPi (ORCPT ); Fri, 9 Sep 2011 09:15:38 -0400 From: Pedro Alves Organization: CodeSourcery To: Denys Vlasenko Subject: Re: [PATCH v3] Make PTRACE_SEIZE set ptrace options specified in 'data' Date: Fri, 9 Sep 2011 14:15:33 +0100 User-Agent: KMail/1.13.6 (Linux/2.6.38-11-generic; KDE/4.7.0; x86_64; ; ) Cc: Oleg Nesterov , Tejun Heo , linux-kernel@vger.kernel.org, Denys Vlasenko References: <1315506333.18043.49.camel@dhcp-25-63.brq.redhat.com> <201109091212.59889.pedro@codesourcery.com> <1315571337.4127.3.camel@dhcp-25-63.brq.redhat.com> In-Reply-To: <1315571337.4127.3.camel@dhcp-25-63.brq.redhat.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <201109091415.33503.pedro@codesourcery.com> X-OriginalArrivalTime: 09 Sep 2011 13:15:36.0138 (UTC) FILETIME=[8FD89AA0:01CC6EF2] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Friday 09 September 2011 13:28:55, Denys Vlasenko wrote: > 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. Well, if you'll remember, back in I raised this exact problem with that pesky racy post-execve SIGTRAP showing through on SEIZE, and Tejun a few replies later mentioned that the SIGTRAP was to be removed on SEIZE. I'm sure it was said before even, but I'm not finding the emails now. > My sense of taste says the approach "you need to use SEIZE to affect > feature " for various unrelated makes ptrace API ugly. Yes, very much agreed! > Especially that in this case, we already have a method in API > to suppress post-execve SIGTRAP. Right, but we end up with no way to make the tracee _not ever stop_ at execve if the tracer wants to, like you can make the tracee not ever stop on forks or syscalls, by not enabling the corresponding PTRACE_O_FOO or not PTRACE_SYSCALL. Not specifying PTRACE_O_TRACEEXEC coupled with `SEIZE not stopping tracees for that magic SIGTRAP' got you that. In a way, it looked to me to make the API a bit less ugly. That said I'm not seeing GDB _not_ using PTRACE_O_TRACEEXEC... Anyway, could you please check (or Tejun please confirm) that that magic SIGTRAP is really still there on SEIZE? -- Pedro Alves