From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757808Ab1EZPD1 (ORCPT ); Thu, 26 May 2011 11:03:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50582 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751930Ab1EZPD0 (ORCPT ); Thu, 26 May 2011 11:03:26 -0400 Date: Thu, 26 May 2011 17:01:50 +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: <20110526150150.GD12525@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> <20110525182919.GB16575@redhat.com> <20110526091401.GD9715@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110526091401.GD9715@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 05/26, Tejun Heo wrote: > > Hello, > > On Wed, May 25, 2011 at 08:29:19PM +0200, Oleg Nesterov wrote: > > > > 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. > > I think we can just make PTRACE_DETACH to succeed for zombies. No > reason to add a new request for this. OK. > > 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. > > Just letting PTRACE_DETACH work for zombies sounds much simpler to me. Probably, but please note we have to modify do_wait() anyway. Otherwise in general the tracer simply can not know the tracee has exited. IOW, waitpid(zombie_leader_pid, WEXITED) should succeed without reaping if delay_group_leader(), then the tracer can do PTRACE_DETACH. But this is not symmetrical with sub-thread zombies. Oleg.