Date: Sat, 13 Nov 2010 13:25:24 +0200 From: Andriy Gapon <avg@freebsd.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: freebsd-fs@freebsd.org, freebsd-stable@freebsd.org Subject: Re: 8.1-STABLE: problem with unmounting ZFS snapshots Message-ID: <4CDE75A4.8050702@freebsd.org> In-Reply-To: <20101113112104.GE2392@deviant.kiev.zoral.com.ua> 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> <20101113112104.GE2392@deviant.kiev.zoral.com.ua>
next in thread | previous in thread | raw e-mail | index | archive | help
on 13/11/2010 13:21 Kostik Belousov said the following: > 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. >>> >>> Before v15 we have been happy with that code and had no issues :-) >>> >>> 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); >>> >>> Now let's say you have a mounted filesystem (e.g. md) under /mnt: >>> /dev/md5 on /mnt (ufs, local) >>> >>> # mkdir /mnt/test >>> # mount -t zfs tank@t2 /mnt/test >>> # umount -f /mnt >>> >>> Now you will hang because the second VFS_HOLD. >> >> 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. Ah, I see now, thank you for the explanation. -- Andriy Gapon
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?4CDE75A4.8050702>