Date: Wed, 26 Aug 2009 23:26:33 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: Rick Macklem <rmacklem@uoguelph.ca> Cc: "Rick C. Petty" <rick-freebsd2008@kiwi-computer.com>, bzeeb+freebsd+lor@zabbadoz.net, current@freebsd.org Subject: Re: various vfs LORs Message-ID: <20090826202633.GF9623@deviant.kiev.zoral.com.ua> In-Reply-To: <Pine.GSO.4.63.0908261041090.21868@muncher.cs.uoguelph.ca> References: <20090819161817.GA89704@keira.kiwi-computer.com> <20090819175029.GA90205@keira.kiwi-computer.com> <Pine.GSO.4.63.0908211402510.14428@muncher.cs.uoguelph.ca> <20090821200957.GC9623@deviant.kiev.zoral.com.ua> <Pine.GSO.4.63.0908261041090.21868@muncher.cs.uoguelph.ca>
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--xcdXf2pmdJ8FA+Zb Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Aug 26, 2009 at 10:48:13AM -0400, Rick Macklem wrote: >=20 >=20 > On Fri, 21 Aug 2009, Kostik Belousov wrote: >=20 > >> > >>Since the 3rd one is locking a newly allocated nfs vnode (that isn't yet > >>in the mount point list, etc), I don't think this will cause a problem > >>and I don't see an easy way to avoid it. > > > >We could add LK_NOWITNESS to nfsclient/nfs_subr.c:161. > > > Ok, I had thought LK_NOWITNESS was used for lockinit() and applied to > the lock "forever" so it didn't seem like a good idea, but I just > looked and it appears that LK_NOWITNESS can be used for > vn_lock()/lockmgr() to apply to that lock call only? >=20 > If so, this seems reasonable, so long as my analysis that it doesn't > matter because it is a new nfs vnode (guaranteed to not yet be locked) > and, as such, can't cause a deadlock. (I'm assuming that LORs are checked > to try and avoid deadlocks or other nasties like sleeping for a sleep lock > when a mutex is held.) Sound right? Yes, sounds right. You could see similar workaround in devfs, fs/devfs/devfs_vnops.c:404, also in the place where new vnode is instantiated. --xcdXf2pmdJ8FA+Zb Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkqVmnkACgkQC3+MBN1Mb4gNhACgqehA5vgHKQVBmFl0u0Pg2x0y 6bsAoLjCJeGSOXRjvdWBaSlF5JNwUQj6 =a+Sc -----END PGP SIGNATURE----- --xcdXf2pmdJ8FA+Zb--
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