From owner-freebsd-current@FreeBSD.ORG Wed Feb 15 16:33:01 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 6AF2F106564A for ; Wed, 15 Feb 2012 16:33:01 +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 6008D8FC08 for ; Wed, 15 Feb 2012 16:32:59 +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 q1FGWr0q060353 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 15 Feb 2012 18:32:53 +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 q1FGWqlE005535; Wed, 15 Feb 2012 18:32:52 +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 q1FGWq8l005534; Wed, 15 Feb 2012 18:32:52 +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 18:32:52 +0200 From: Konstantin Belousov To: Dmitry Mikulin Message-ID: <20120215163252.GZ3283@deviant.kiev.zoral.com.ua> References: <4F31C89C.7010705@juniper.net> <4F3318AD.6000607@juniper.net> <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> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="VtOb4vV0nsUnkr3G" Content-Disposition: inline In-Reply-To: <4F3993C5.5020703@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 16:33:01 -0000 --VtOb4vV0nsUnkr3G Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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 would > >>>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=20 > >>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 wh= ile > >>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 keep= =20 > >>the > >>orphan list clean and not have the same entries and the list of sibling= s. > >Right, this is what I figured. But I asked about some further implication > >of this change: > > > >if real parent spuriosly calls wait4(2) on the child pid after the child > >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 ? >=20 > In this case the process will move from gdb's child list to gdb's orphan= =20 > list when the real parent does a wait4(). Next time around the wait loop = in=20 > 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. --VtOb4vV0nsUnkr3G Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (FreeBSD) iEYEARECAAYFAk873jQACgkQC3+MBN1Mb4g9UgCg3EUpfudY7esu+R4cGFrYauYh I7MAoKd6qEKZCGU7SXwWgKWL2kN77QdQ =QwmM -----END PGP SIGNATURE----- --VtOb4vV0nsUnkr3G--