From owner-svn-src-all@FreeBSD.ORG Wed Sep 26 20:02:07 2012 Return-Path: Delivered-To: svn-src-all@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 16904106566C; Wed, 26 Sep 2012 20:02:07 +0000 (UTC) (envelope-from pawel@dawidek.net) Received: from mail.dawidek.net (garage.dawidek.net [91.121.88.72]) by mx1.freebsd.org (Postfix) with ESMTP id A052B8FC17; Wed, 26 Sep 2012 20:02:06 +0000 (UTC) Received: from localhost (89-73-195-149.dynamic.chello.pl [89.73.195.149]) by mail.dawidek.net (Postfix) with ESMTPSA id 6C8ACA79; Wed, 26 Sep 2012 22:01:05 +0200 (CEST) Date: Wed, 26 Sep 2012 22:02:31 +0200 From: Pawel Jakub Dawidek To: "Kenneth D. Merry" Message-ID: <20120926200231.GD1402@garage.freebsd.pl> References: <201209221241.q8MCfnhJ067937@svn.freebsd.org> <20120925233712.GA26920@nargothrond.kdm.org> <20120926072005.GH1391@garage.freebsd.pl> <20120926172917.GA71268@nargothrond.kdm.org> <20120926185339.GA1402@garage.freebsd.pl> <20120926192117.GA89741@nargothrond.kdm.org> <20120926194541.GB1402@garage.freebsd.pl> <20120926195820.GA96844@nargothrond.kdm.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="cHMo6Wbp1wrKhbfi" Content-Disposition: inline In-Reply-To: <20120926195820.GA96844@nargothrond.kdm.org> X-OS: FreeBSD 10.0-CURRENT amd64 User-Agent: Mutt/1.5.21 (2010-09-15) Cc: svn-src-head@FreeBSD.org, jdp@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, phk@FreeBSD.org Subject: Re: svn commit: r240822 - head/sys/geom X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 26 Sep 2012 20:02:07 -0000 --cHMo6Wbp1wrKhbfi Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Sep 26, 2012 at 01:58:20PM -0600, Kenneth D. Merry wrote: > On Wed, Sep 26, 2012 at 21:45:41 +0200, Pawel Jakub Dawidek wrote: > > On Wed, Sep 26, 2012 at 01:21:17PM -0600, Kenneth D. Merry wrote: > > > On Wed, Sep 26, 2012 at 20:53:39 +0200, Pawel Jakub Dawidek wrote: > > > > On Wed, Sep 26, 2012 at 11:29:17AM -0600, Kenneth D. Merry wrote: > > > > > Here is what CAM needs at each step: > > > > >=20 > > > > > 1. When a device goes away, we need a method to call from daonin= validate() > > > > > (or any other peripheral driver invalidate routine) with these > > > > > properties: > > > > > - It tells GEOM that the device has gone away, and starts the= process > > > > > of shutting down the device. (i.e. withers/orphans the pro= vider) > > > > > - It is callable from an interrupt context, with the SIM (MTX= _DEF) lock > > > > > held, so it can't sleep. > > > >=20 > > > > Neither g_wither_provider() nor g_orphan_provider() require the top= ology > > > > lock. They only acquire the event lock, but it is regular mutex, so= this > > > > is fine. Traversing geom's providers list looks like something that= does > > > > need the topology lock, but maybe traversing is not needed at all. > > > > The reason for this change was a panic in iSCSI initiator where > > > > disk_gone() was called and provider was destroyed before g_wither_g= eom() > > > > returned. > > >=20 > > > Ahh. How about using LIST_FOREACH_SAFE? Would that address the prob= lem at > > > hand? Are there any other races in there? > >=20 > > It depends. If one geom can hold more than one provider then it might be > > racy, but from what I see there is always only one provider - there has > > to be only one, because disk_destroy() destroys it and struct disk > > represents always only one disk. If that's true then I see not reason to > > have a loop in there. I'd change it to: > >=20 > > void > > disk_gone(struct disk *dp) > > { > > struct g_geom *gp; > > struct g_provider *pp; > >=20 > > gp =3D dp->d_geom; > > if (gp !=3D NULL) { > > pp =3D LIST_FIRST(&gp->provider); > > if (pp !=3D NULL) > > g_wither_provider(pp, ENXIO); > > } > > } >=20 > I would suggest doing LIST_FOREACH_SAFE() (with a comment explaining why) > instead. That way just in case someone adds another provider down the > road it will be handled properly. >=20 > Otherwise we need a comment or KASSERT somewhere to explain that we depend > on there only being one provider, and things will break if there is more > than one. I'm happy with adding KASSERT(), as I don't believe LIST_FOREACH_SAFE() will be safe there, as disk_gone() itself doesn't prevent the function to be called for two different disks, but one geom. LIST_FOREACH_SAFE() make it safe to remove only the current element. If any other elements is removed while we are traversing the list it will most likely panic. --=20 Pawel Jakub Dawidek http://www.wheelsystems.com FreeBSD committer http://www.FreeBSD.org Am I Evil? Yes, I Am! http://tupytaj.pl --cHMo6Wbp1wrKhbfi Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iEYEARECAAYFAlBjX1cACgkQForvXbEpPzSMJgCg73NO/1D9VJ4C/VVuZIaFcYza VRkAoL5oBoteiXlxenpEJK6kio2SmbId =DaJ2 -----END PGP SIGNATURE----- --cHMo6Wbp1wrKhbfi--