Date: Mon, 13 Jun 2011 22:20:31 +0200 From: Pawel Jakub Dawidek <pjd@FreeBSD.org> To: "K. Macy" <kmacy@freebsd.org> Cc: fs@freebsd.org Subject: Re: Drop of spa_namespace lock in vdev_geom.c Message-ID: <20110613202031.GB1733@garage.freebsd.pl> In-Reply-To: <BANLkTimUNQg_9Y94FTZnijOU%2Bp=QK3JV3A@mail.gmail.com> References: <4DF25544.3020301@FreeBSD.org> <BANLkTimUNQg_9Y94FTZnijOU%2Bp=QK3JV3A@mail.gmail.com>
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--ftEhullJWpWg/VHq Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Jun 10, 2011 at 09:35:08PM +0200, K. Macy wrote: > On Fri, Jun 10, 2011 at 7:32 PM, Justin T. Gibbs <gibbs@freebsd.org> wrot= e: > > Dropping and reacquiring the spa_namespace lock in vdev_geom_open() > > creates a lock order reversal with the spa_config locks. =A0As the > > spa_config locks are not standard mutexes, witness will not warn > > about this issue. >=20 > The real problem is that WITNESS is disabled on the sx locks used for > mutex compatibility in ZFS. This questionable decision has made > debugging deadlocks quite painful on a number of occasions. I think > this choice should be revisited and perhaps special workaround shims > added for cases where cv_wait is called. WITNESS is disabled only if you are compiling ZFS without debug. This was done because of huge number of false-positive LOR reports from users. If you are developing ZFS you should have debug turned on anyway. I had a patch for additional sx-creation flag to tell witness that we don't want LOR reports, but we still want to track the lock itself, but there were no agreement among people I talked to about that, so it never went in. --=20 Pawel Jakub Dawidek http://www.wheelsystems.com FreeBSD committer http://www.FreeBSD.org Am I Evil? Yes, I Am! http://yomoli.com --ftEhullJWpWg/VHq Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.14 (FreeBSD) iEYEARECAAYFAk32cQ4ACgkQForvXbEpPzSgMgCfYTiI2LqbDzOBfnBeItLGY7NH BRYAoNZ3G4LcZugdHtnjJZ1vK2SBhMWu =JE2c -----END PGP SIGNATURE----- --ftEhullJWpWg/VHq--
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