From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753286Ab1EYSar (ORCPT ); Wed, 25 May 2011 14:30:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:5962 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752643Ab1EYSaq (ORCPT ); Wed, 25 May 2011 14:30:46 -0400 Date: Wed, 25 May 2011 20:29:19 +0200 From: Oleg Nesterov To: Tejun Heo Cc: Denys Vlasenko , jan.kratochvil@redhat.com, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, indan@nul.nu, bdonlan@gmail.com Subject: Re: [PATCH 03/10] ptrace: implement PTRACE_SEIZE Message-ID: <20110525182919.GB16575@redhat.com> References: <1305569849-10448-1-git-send-email-tj@kernel.org> <1305569849-10448-4-git-send-email-tj@kernel.org> <201105180240.56754.vda.linux@googlemail.com> <20110518095539.GU20624@htj.dyndns.org> <20110523124314.GA7232@redhat.com> <20110524102834.GC10334@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110524102834.GC10334@htj.dyndns.org> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/24, Tejun Heo wrote: > > Hello, Oleg. > > On Mon, May 23, 2011 at 02:43:14PM +0200, Oleg Nesterov wrote: > > On 05/18, Tejun Heo wrote: > > > I've been thinking about Jan's suggestion to make ATTACH and DETACH > > > not require tracee to trap. We already have this for DETACH for cases > > > where the tracer is killed > > > > Yes, I still think that the new DETACH_XXX request which doesn't need > > the stopped tracee makes sense. Yes, we have PTRACE_INTERRUPT. But please > > recall the previous discussion, it is possible that the tracee can't > > react to PTRACE_INTERRUPT and trap because it waits for other threads > > we are tracing. > > Yeah, untrapped DETACH sounds nice but as you've already acknowledged > in another reply, we have those nasty disable traps. Yes. Which I never thought about, I alway assume PTRACE_DETACH_ASYNC is trivial, but it is not. Lets forget it for now. > > And. Currently there is no way to detach a zombie leader. Perhaps we > > should change do_wait(), but it is not clear what should we do if the > > tracer is the real parent (we already discussed this a bit). > > Hmmm... maybe just allow detaching zombie leader? Yes, I think we should do this. If we change PTRACE_DETACH (or add the new request) to allow this, then I think it it should detach any zombie, leader or not. Or we can change do_wait() to detach a zombie leader. In this case it is not clear what should we do if the debugger is the real parent. Perhaps do_wait() should do the same: detach a leader (but not reap). When the last thread does, the real parent will be notified again. IOW, wait(tgid) can succeed twice. > As it's guaranteed > to be not running, we don't have problem with ptrace_disable. Agreed. In fact it can be running, but it can't return to the user-space, and I think this is enough. ptrace_detach()->ptrace_disable() can race with SIGKILL anyway, this means it should safe to call it if the tracee is exiting/exited. Oleg.