From owner-freebsd-current@FreeBSD.ORG Wed Feb 15 17:40:39 2012 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 35598106564A for ; Wed, 15 Feb 2012 17:40:39 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from mail.zoral.com.ua (mx0.zoral.com.ua [91.193.166.200]) by mx1.freebsd.org (Postfix) with ESMTP id BCC9D8FC13 for ; Wed, 15 Feb 2012 17:40:38 +0000 (UTC) Received: from skuns.kiev.zoral.com.ua (localhost [127.0.0.1]) by mail.zoral.com.ua (8.14.2/8.14.2) with ESMTP id q1FHeV1S066473 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 15 Feb 2012 19:40:32 +0200 (EET) (envelope-from kostikbel@gmail.com) Received: from deviant.kiev.zoral.com.ua (kostik@localhost [127.0.0.1]) by deviant.kiev.zoral.com.ua (8.14.5/8.14.5) with ESMTP id q1FHeVW0005921; Wed, 15 Feb 2012 19:40:31 +0200 (EET) (envelope-from kostikbel@gmail.com) Received: (from kostik@localhost) by deviant.kiev.zoral.com.ua (8.14.5/8.14.5/Submit) id q1FHeV7o005920; Wed, 15 Feb 2012 19:40:31 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: deviant.kiev.zoral.com.ua: kostik set sender to kostikbel@gmail.com using -f Date: Wed, 15 Feb 2012 19:40:31 +0200 From: Konstantin Belousov To: Dmitry Mikulin Message-ID: <20120215174031.GB3283@deviant.kiev.zoral.com.ua> References: <20120209122908.GD3283@deviant.kiev.zoral.com.ua> <4F34311A.9050702@juniper.net> <20120210001725.GJ3283@deviant.kiev.zoral.com.ua> <4F3478B3.9040809@juniper.net> <20120213152825.GH3283@deviant.kiev.zoral.com.ua> <4F3988E8.2040705@juniper.net> <20120213222521.GK3283@deviant.kiev.zoral.com.ua> <4F3993C5.5020703@juniper.net> <20120215163252.GZ3283@deviant.kiev.zoral.com.ua> <4F3BE9C2.8040908@juniper.net> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="kafhcBLPEB+rLNbV" Content-Disposition: inline In-Reply-To: <4F3BE9C2.8040908@juniper.net> User-Agent: Mutt/1.4.2.3i X-Virus-Scanned: clamav-milter 0.95.2 at skuns.kiev.zoral.com.ua X-Virus-Status: Clean X-Spam-Status: No, score=-3.9 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on skuns.kiev.zoral.com.ua Cc: freebsd-current Current , Marcel Moolenaar Subject: Re: [ptrace] please review follow fork/exec changes X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 15 Feb 2012 17:40:39 -0000 --kafhcBLPEB+rLNbV Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Feb 15, 2012 at 09:22:10AM -0800, Dmitry Mikulin wrote: >=20 >=20 > On 02/15/2012 08:32 AM, Konstantin Belousov wrote: > >On Mon, Feb 13, 2012 at 02:50:45PM -0800, Dmitry Mikulin wrote: > >>>>>It seems that now wait4(2) can be called from the real (non-debugger) > >>>>>parent first and result in the call to proc_reap(), isn't it ? We wo= uld > >>>>>then just reparent the child back to the caller, still leaving the > >>>>>zombie and confusing debugger. > >>>>When either gdb or the real parent gets to proc_reap() the process > >>>>wouldn't > >>>>get destroyed, it'll get caught by the following clause: > >>>> if (p->p_oppid&& (t =3D pfind(p->p_oppid)) !=3D NULL) { > >>>> > >>>>and the real parent with get the child back into the children's list= =20 > >>>>while > >>>>gdb will get it into the orphan list. The second time around when > >>>>proc_reap() is entered, p->p_oppid will be 0 and the process will get > >>>>really reaped. Does it make sense? And proc_reparent() attempts to ke= ep > >>>>the > >>>>orphan list clean and not have the same entries and the list of=20 > >>>>siblings. > >>>Right, this is what I figured. But I asked about some further implicat= ion > >>>of this change: > >>> > >>>if real parent spuriosly calls wait4(2) on the child pid after the chi= ld > >>>exited, but before the debugger called the wait4(), then exactly the > >>>code you noted above will be run. This results in the child being fully > >>>returned to the original parent. > >>> > >>>Next, the wait4() call from debugger gets an error, and zombie will be > >>>kept around until parent calls wait4() for this pid once more. > >>> > >>>Am I missed something ? > >>In this case the process will move from gdb's child list to gdb's orphan > >>list when the real parent does a wait4(). Next time around the wait loo= p=20 > >>in > >>gdb it'll be caught by the orphan's proc_reap(). > >I do not see how the next debugger loop could find this process at all, > >since the first wait4() call reparented it to the original parent. >=20 > Not the debugger loop, the kern_wait() loop. The child get re-parented to= =20 > the original parent but moves to the orphan list of the debugger process. Either the debugger loop which calls wait4/waitpid, or the kern_wait loop resulting from the debugger calling wait*. Could you, please, describe, how the patched kernel moves the wait'ed zombie to the orphan list of the debugger ? For me, it seems that there is another bug, the child appears both on the childdren list, and on the orphan list of the real parent. --kafhcBLPEB+rLNbV Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAk877g8ACgkQC3+MBN1Mb4hE7wCdEVmWWBP04dzRuzjjoTyg3G5g QloAn2i2EukBi9Nen0Z+XVPhFQR/fyGs =cXeQ -----END PGP SIGNATURE----- --kafhcBLPEB+rLNbV--