On Tue, Apr 17, 2012 at 11:32:46AM +0200, Jan Kara wrote: > On Mon 16-04-12 15:02:50, Andreas Dilger wrote: > > On 2012-04-16, at 9:13 AM, Jan Kara wrote: > > > Another potential contention point might be patch 19. In that patch > > > we make freeze_super() refuse to freeze the filesystem when there > > > are open but unlinked files which may be impractical in some cases. > > > The main reason for this is the problem with handling of file deletion > > > from fput() called with mmap_sem held (e.g. from munmap(2)), and > > > then there's the fact that we cannot really force such filesystem > > > into a consistent state... But if people think that freezing with > > > open but unlinked files should happen, then I have some possible > > > solutions in mind (maybe as a separate patchset since this is > > > large enough). > > > > Looking at a desktop system, I think it is very typical that there > > are open-unlinked files present, so I don't know if this is really > > an acceptable solution. It isn't clear from your comments whether > > this is a blanket refusal for all open-unlinked files, or only in > > some particular cases... > Thanks for looking at this. It is currently a blanket refusal. And I > agree it's problematic. There are two problems with open but unlinked > files. Let me add my name to the chorus of "we have to handle freezing with open+unlinked, we cannot assume they don't exist." > One is that some old filesystems cannot get in a consistent state in > presence of open but unlinked files but for filesystems we really care > about - xfs, ext4, ext3, btrfs, or even ocfs2, gfs2 - that is not a real > issue (these filesystems will delete those inodes on next mount read-write). Others have pointed out that we can flag the safe filesystems. I'd even be willing to say you can't freeze the unsafe filesystems. > The other problem is with what should happen when you put last inode > reference on a frozen filesystem. Two possibilities I see are: > > a) block the iput() call - that is inconvenient because it can be > called in various contexts. I think we could possibly use the same level of > freeze protection as for page fault (this has changed since I originally > thought about this and that would make things simpler) but I'm not > completely sure. Given that frozen filesystems can stay that way for a while, couldn't that lead to a million frozen df(1)s? It's like your average NFS network failure. > b) let the iput finish but filesystem will keep inode on its orphan list > (or it's equivalent) and the inode will be deleted after the filesystem is > thawed. The advantage of this is we don't have to block iput(), the > disadvantage is we have to have filesystem support and not all filesystems > can do this. Perhaps we handle iput() like unlinked. If the filesystem can handle it, we allow it, otherwise we block. Joel > > Any thoughts? > > Honza > > > > lsof | grep deleted > > nautilus 25393 adilger 19r REG 253,0 340 253954 /home/adilger/.local/share/gvfs-metadata/home (deleted) > > nautilus 25393 adilger 20r REG 253,0 32768 253964 /home/adilger/.local/share/gvfs-metadata/home-f332a8f3.log (deleted) > > gnome-ter 25623 adilger 22u REG 0,18 17841 2717846 /tmp/vtePIRJCW (deleted) > > gnome-ter 25623 adilger 23u REG 0,18 5568 2717847 /tmp/vteDCSJCW (deleted) > > gnome-ter 25623 adilger 29u REG 0,18 480 2728484 /tmp/vte6C1TCW (deleted) > > -- > Jan Kara <jack@xxxxxxx> > SUSE Labs, CR -- "The first requisite of a good citizen in this republic of ours is that he shall be able and willing to pull his weight." - Theodore Roosevelt http://www.jlbec.org/ jlbec@xxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
