Date: Sat, 13 Nov 2010 12:06:27 +0100 From: Martin Matuska <mm@FreeBSD.org> To: Andriy Gapon <avg@freebsd.org> Cc: freebsd-fs@freebsd.org, freebsd-stable@freebsd.org Subject: Re: 8.1-STABLE: problem with unmounting ZFS snapshots Message-ID: <4CDE7133.6010803@FreeBSD.org> In-Reply-To: <4CDE6823.6080907@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>
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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. 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. Dňa 13.11.2010 11:27, Andriy Gapon wrote / napísal(a): > on 13/11/2010 04:27 Martin Matuska said the following: >> Yes, this is indeed a leak introduced by importing onnv revision 9214 >> and it exists in perforce as well - very easy to reproduce. >> >> # mount -t zfs test@t1 /mnt >> # umount /mnt (-> hang) >> >> http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6604992 >> http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6810367 >> >> This is not compatible with mounting snapshots outside mounted ZFS and I >> was not able to reproduce the errors defined in 6604992 and 6810367 >> (they are Solaris-specific). I suggest we comment out this code (from >> head, later MFC and p4 as well). >> >> Patch (should work with HEAD and 8-STABLE): >> http://people.freebsd.org/~mm/patches/zfs/zfs_vfsops.c.patch > > Not quite sure, but perhaps it's better to make the logic in each place match > the other. That is, I see that the code does hold on a filesystem of a covered > vnode, but does rele on a parent ZFS filesystem. > Or is this kind of protection not needed at all for FreeBSD? >
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