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    SubjectRe: [PATCH 00/19 v5] Fix filesystem freezing deadlocks
    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

    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).

    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.

    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.

    Any thoughts?

    > 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 <>
    SUSE Labs, CR

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