Date: Mon, 28 Mar 2011 00:06:38 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Mikolaj Golub <trociny@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r220062 - head/sys/geom/gate Message-ID: <20110327210638.GO78089@deviant.kiev.zoral.com.ua> In-Reply-To: <86fwq8e1bo.fsf@kopusha.home.net> References: <201103271956.p2RJutha067490@svn.freebsd.org> <20110327200804.GM78089@deviant.kiev.zoral.com.ua> <86fwq8e1bo.fsf@kopusha.home.net>
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--bF/koNWjw4RKgJoH Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, Mar 27, 2011 at 11:49:15PM +0300, Mikolaj Golub wrote: >=20 > On Sun, 27 Mar 2011 23:08:04 +0300 Kostik Belousov wrote: >=20 > KB> On Sun, Mar 27, 2011 at 07:56:55PM +0000, Mikolaj Golub wrote: > >> Author: trociny > >> Date: Sun Mar 27 19:56:55 2011 > >> New Revision: 220062 > >> URL: http://svn.freebsd.org/changeset/base/220062 > >>=20 > >> Log: > >> In g_gate_create() there is a window between when g_gate_softc is > >> registered in g_gate_units array and when its sc_provider field is > >> filled. If during this period g_gate_units is accessed by another > >> thread that is checking for provider name collision the crash is > >> possible. > >> =20 > >> Fix this by adding sc_name field to struct g_gate_softc. In > >> g_gate_create() when g_gate_softc is created but sc_provider is sti= ll > >> not sc_name points to provider name stored in the local array. > >> =20 > >> Approved by: pjd (mentor) > >> Reported by: Freddie Cash <fjwcash@gmail.com> > >> MFC after: 1 week > >>=20 > >> Modified: > >> head/sys/geom/gate/g_gate.c > >> head/sys/geom/gate/g_gate.h > >>=20 > >> Modified: head/sys/geom/gate/g_gate.c > >> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D > >> --- head/sys/geom/gate/g_gate.c Sun Mar 27 19:29:18 2011 = (r220061) > >> +++ head/sys/geom/gate/g_gate.c Sun Mar 27 19:56:55 2011 = (r220062) > >> @@ -409,13 +409,14 @@ g_gate_create(struct g_gate_ctl_create * > >> for (unit =3D 0; unit < g_gate_maxunits; unit++) { > >> if (g_gate_units[unit] =3D=3D NULL) > >> continue; > >> - if (strcmp(name, g_gate_units[unit]->sc_provider->na= me) !=3D 0) > >> + if (strcmp(name, g_gate_units[unit]->sc_name) !=3D 0) > >> continue; > >> mtx_unlock(&g_gate_units_lock); > >> mtx_destroy(&sc->sc_queue_mtx); > >> free(sc, M_GATE); > >> return (EEXIST); > >> } > >> + sc->sc_name =3D name; > >> g_gate_units[sc->sc_unit] =3D sc; > >> g_gate_nunits++; > >> mtx_unlock(&g_gate_units_lock); > >> @@ -434,6 +435,9 @@ g_gate_create(struct g_gate_ctl_create * > >> sc->sc_provider =3D pp; > >> g_error_provider(pp, 0); > >> g_topology_unlock(); > >> + mtx_lock(&g_gate_units_lock); > >> + sc->sc_name =3D sc->sc_provider->name; > >> + mtx_unlock(&g_gate_units_lock); > KB> I think you do not need a mutex locked around the single assignment. > KB> As I understand, sc_provider->name is constant ? >=20 > Is the following scenario impossible? >=20 > Thread A is looking for name collision and is accessing > g_gate_units[unit]->sc_name of the unit that is being created by a thread= B, > so sc_name is pointing to thread B local buffer. At this time the thread B > creates provider, does sc->sc_name =3D sc->sc_provider->name and returns = from > g_gate_create(). Thread A, if it is still working with > g_gate_units[unit]->sc_name, is accessing invalid memory. Ok, name is local variable. Apparently, what you need is a barrier. It would be enough to do sc->sc_name =3D sc->sc_provider->name; mtx_lock(&g_gate_units_lock); mtx_unlock(&g_gate_units_lock); The change is fine as is. --bF/koNWjw4RKgJoH Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEARECAAYFAk2Ppt0ACgkQC3+MBN1Mb4gKPgCfVcIJo1XtYN4nG1gd/akhD2o9 KUYAnRIFG+ZjE+9FLCexAdSG7D+PCFo0 =797P -----END PGP SIGNATURE----- --bF/koNWjw4RKgJoH--
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