Date: Sat, 13 Nov 2010 13:09:55 +0200 From: Andriy Gapon <avg@freebsd.org> To: Martin Matuska <mm@freebsd.org> Cc: freebsd-fs@freebsd.org, freebsd-stable@freebsd.org Subject: Re: 8.1-STABLE: problem with unmounting ZFS snapshots Message-ID: <4CDE7203.7090507@freebsd.org> In-Reply-To: <4CDE7133.6010803@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>
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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. > 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. -- Andriy Gapon
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