From owner-svn-src-head@FreeBSD.ORG Mon Jun 23 07:25:25 2014 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 80430844; Mon, 23 Jun 2014 07:25:25 +0000 (UTC) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 1F7CD2697; Mon, 23 Jun 2014 07:25:24 +0000 (UTC) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.14.9/8.14.9) with ESMTP id s5N7PJoi067255; Mon, 23 Jun 2014 10:25:19 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.8.3 kib.kiev.ua s5N7PJoi067255 Received: (from kostik@localhost) by tom.home (8.14.9/8.14.8/Submit) id s5N7PJ0S067254; Mon, 23 Jun 2014 10:25:19 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Mon, 23 Jun 2014 10:25:19 +0300 From: Konstantin Belousov To: Mateusz Guzik Subject: Re: svn commit: r267760 - head/sys/kern Message-ID: <20140623072519.GE93733@kib.kiev.ua> References: <201406230128.s5N1SIYK097224@svn.freebsd.org> <20140623064044.GD93733@kib.kiev.ua> <20140623070652.GA27040@dft-labs.eu> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="ytoMbUMiTKPMT3hY" Content-Disposition: inline In-Reply-To: <20140623070652.GA27040@dft-labs.eu> User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.0 X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on tom.home Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, Mateusz Guzik X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 23 Jun 2014 07:25:25 -0000 --ytoMbUMiTKPMT3hY Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Jun 23, 2014 at 09:06:52AM +0200, Mateusz Guzik wrote: > On Mon, Jun 23, 2014 at 09:40:44AM +0300, Konstantin Belousov wrote: > > On Mon, Jun 23, 2014 at 01:28:18AM +0000, Mateusz Guzik wrote: > > > + KASSERT(fdp->fd_refcnt =3D=3D 1, ("the fdtable should not be shared= ")); > > > FILEDESC_XLOCK(fdp); > > This is at least weird. Not incorrect, but the code now looks strange. > > The fd_refcnt =3D=3D 1 assert just states the circumstances of the code= which > > currently calls the functions. Would the functions become incorrect or > > destructive if there are other references to the filedescriptor table ? > >=20 > > In case you argument is that refcnt =3D=3D 1 must hold to prevent the p= arallel > > modifications of the descriptor table, which would invalidate the checks > > and actions of the functions, then XLOCK is not needed (similar to your > > earlier commit). > >=20 > > Note that kern_execve() is executed with the process single-threaded, > > which, together with statement fd_refcnt =3D=3D 1 must prevent the para= llel > > modifications. >=20 > The table is modified in these functions and is reachable from the rest > of the kernel (can be found by e.g. sysctl_kern_proc_filedesc), thus > XLOCK is needed to ensure consistency for readers. It can also be > altered by mountcheckdirs, although not in a way which disrupts any of > these functions. I would think that such cases should be avoided by testing for P_INEXEC, but I do not insist on this. >=20 > For now I do agree that both the assertion and XLOCK look weird as it is > and as such deserve a comment. >=20 > Actually we can take the lock only if we are going to modify something. >=20 > How about the following then (untested): See below, but I would be completely satisfied even by only comment addition. >=20 > diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c > index 25c3a1e..31f4881 100644 > --- a/sys/kern/kern_descrip.c > +++ b/sys/kern/kern_descrip.c > @@ -2082,13 +2082,18 @@ setugidsafety(struct thread *td) > int i; > =20 > fdp =3D td->td_proc->p_fd; > + /* > + * While no other thread can alter filedescriptors in this table, > + * there may be code trying to read it, thus the lock is required > + * to provide consistent view if we are going to change it. > + */ > KASSERT(fdp->fd_refcnt =3D=3D 1, ("the fdtable should not be shar= ed")); > - FILEDESC_XLOCK(fdp); > for (i =3D 0; i <=3D fdp->fd_lastfile; i++) { > if (i > 2) > break; > fp =3D fdp->fd_ofiles[i].fde_file; > if (fp !=3D NULL && is_unsafe(fp)) { > + FILEDESC_XLOCK(fdp); > knote_fdclose(td, i); > /* > * NULL-out descriptor prior to close to avoid > @@ -2097,7 +2102,6 @@ setugidsafety(struct thread *td) > fdfree(fdp, i); > FILEDESC_XUNLOCK(fdp); > (void) closef(fp, td); > - FILEDESC_XLOCK(fdp); > } > } > FILEDESC_XUNLOCK(fdp); This unlock should be removed ? > @@ -2136,16 +2140,16 @@ fdcloseexec(struct thread *td) > =20 > fdp =3D td->td_proc->p_fd; > KASSERT(fdp->fd_refcnt =3D=3D 1, ("the fdtable should not be shar= ed")); > - FILEDESC_XLOCK(fdp); > for (i =3D 0; i <=3D fdp->fd_lastfile; i++) { > fde =3D &fdp->fd_ofiles[i]; > fp =3D fde->fde_file; > if (fp !=3D NULL && (fp->f_type =3D=3D DTYPE_MQUEUE || > (fde->fde_flags & UF_EXCLOSE))) { > + /* See the comment in setugidsafety */ > + FILEDESC_XLOCK(fdp); > fdfree(fdp, i); > (void) closefp(fdp, i, fp, td, 0); > /* closefp() drops the FILEDESC lock. */ > - FILEDESC_XLOCK(fdp); This should be XUNLOCK ? > } > } > FILEDESC_XUNLOCK(fdp); And this unlock removed ? >=20 >=20 > --=20 > Mateusz Guzik --ytoMbUMiTKPMT3hY Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBAgAGBQJTp9ZeAAoJEJDCuSvBvK1BAcAP/jB9jwxozqXmgeQjWzGyFKjK TnVv3ueKPh/vsWVnQZa/kaRmVyyTU5e9BlhmRKCgbvklU06KLkO729khGIESp15A jeNjR+LBxq6Zq5HjV/1Kdy6VMP/apqnYWc53vwxPdy2sjBgdOrYjBtnuQqfblcfK QtAjIJ7b8aF4iJ/2Ijs2Xq0dDNzS2naoNBGGOlA8fayrw0BPs4h9oTVZUvnq+c8z /FgMNk7D+0M7ghOhsAlAiNyp1ElG6piVKfVNKaqVwDs8ZGQtYyXaw7XGIkNcRMVx 3uNCCtYSG7+DPQUP8yo4sRusDHZnzUti8EOvhHTS76FUcprjUEe1OsIoyVkM4axD wKipFm3viuCEe+RFmo97tG8uHiVlMeNN7G1i3AwKRL0wyEGm0A3mrOO8lRbZNeOu oKtmgZHdgGM8gTAG69bPTpD7wQUgDr5gpSkTYO/9E82LnXmWfHCl68hioAyAC0RD yzmnpuQ/S4gRQjSBImp3TqQsEmHnZqBWqq+g6q+fC6fCKbe5k+KRptOWERpAWRxG V8Q/zbxEa/gUcVXphPR4GL6rq5L5KWvNi9B3p7aSoTS4OYPWhy6b3BkM51p8Qqbm i1OK++xdmJ4/e9fTXkB62BLQV7jwAPn4pk+ziW3qBbRTFZGLfE4KloiQk8U7nGEV QN9uXb728IYlj9yePGvT =5RZm -----END PGP SIGNATURE----- --ytoMbUMiTKPMT3hY--