Date: Sat, 13 Nov 2010 13:21:04 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: Andriy Gapon <avg@freebsd.org> Cc: freebsd-fs@freebsd.org, freebsd-stable@freebsd.org, Martin Matuska <mm@freebsd.org> Subject: Re: 8.1-STABLE: problem with unmounting ZFS snapshots Message-ID: <20101113112104.GE2392@deviant.kiev.zoral.com.ua> In-Reply-To: <4CDE7203.7090507@freebsd.org> References: <D9ABDE54892A4D9285FE7FFA6E1B1B69@vosz.local> <4CDD2F5F.2000902@freebsd.org> <FD7FC6ED159249338A04BE125941D146@vosz.local> <4CDD4EB4.40004@freebsd.org> <4CDDF77B.90708@FreeBSD.org> <4CDE6823.6080907@freebsd.org> <4CDE7133.6010803@FreeBSD.org> <4CDE7203.7090507@freebsd.org>
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--QrrxbCYKnJeJBlX9 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Nov 13, 2010 at 01:09:55PM +0200, Andriy Gapon wrote: > on 13/11/2010 13:06 Martin Matuska said the following: > > No, this is not good for us. Solaris does not allow "mounting" of > > snapshots on any vnode, like we do. Solaris has them only in > > .zfs/snapshots. This allows us to have read-only mounts without even > > mounting the parent zfs. > >=20 > > Before v15 we have been happy with that code and had no issues :-) > >=20 > > I have a very simple testcase where just fixing the VFS_RELE breaks our > > forced unmount. Let's say we use the correct VFS_RELE in zfs_vfsops.c: > > VFS_RELE(vfsp->mnt_vnodecovered->v_vfsp); > >=20 > > Now let's say you have a mounted filesystem (e.g. md) under /mnt: > > /dev/md5 on /mnt (ufs, local) > >=20 > > # mkdir /mnt/test > > # mount -t zfs tank@t2 /mnt/test > > # umount -f /mnt > >=20 > > Now you will hang because the second VFS_HOLD. >=20 > Hang here would be bad, I agree. > But I think that the umount shouldn't succeed either, in this case. Normal unmount indeed shall not succeed in this case, because mount adds a reference to the covered vnode. But forced unmount should be allowed to proceed. After unmount, you can use fsid to unmount the lower mount point. >=20 > > So I stick to my opinion > > that this "extra protection" is more a problem than a solution in our > > case and it should be commented out. >=20 >=20 > --=20 > Andriy Gapon > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" --QrrxbCYKnJeJBlX9 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEARECAAYFAkzedJ8ACgkQC3+MBN1Mb4iVbACg9BjzaWe4CKTTgoiDq/g3eJab gxIAoPIu6gsaPqGxSYGORw1XUPtuAgSx =P5Rh -----END PGP SIGNATURE----- --QrrxbCYKnJeJBlX9--
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