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    SubjectRe: [PATCH] configfs: Silence lockdep on mkdir(), rmdir() and configfs_depend_item()
    On 18/12/08 11:26 +0000, Steven Whitehouse wrote:
    > On Thu, 2008-12-18 at 01:27 -0800, Joel Becker wrote:
    > >
    > > It's about the default_groups and how they build up and tear
    > > down small bits of tree.
    > > A simple creation of a config_item, a mkdir(2), is a normal VFS
    > > lock set and doesn't make lockdep unhappy. But if the new config_item
    > > has a default_group or two, they need locking too. Not so much on
    > > mkdir(2), but on rmdir(2).
    > >
    > So if I've understood this correctly, the dentries created upon mkdir
    > live until such time as they are removed at some later date, presumably
    > with rmdir?
    > When creating the tree, would it be possible to build it starting from
    > the bottom and working towards the point of attachment and then to not
    > actually attach it until the last moment? That way it would not be
    > visible from userland until it was linked into the existing dir and that
    > solves the locking issue for mkdir I think.
    > As you say, rmdir seems the harder problem, but again, is it possible to
    > separate the unlink operation from the destruction of the tree by
    > keeping the tree, after its been unlinked, until the last userland
    > reference has gone away? At least I assume that is why the locking is
    > there. I may be a bit off the mark, but it seems like this is quite
    > similar to how the VFS does umount, so maybe there are some hints in
    > that code which may help us solve this issue?

    I second this kind of rework and even think that it is doable. This would avoid
    exposing things to userspace before they are created for sure. I even had to
    include dirty hacks in configfs to avoid exposing too much of such temporary
    things, and I'm definitely not proud of this.
    Unfortunately I don't have time to rework configfs this way at all.


    Dr Louis Rilling Kerlabs
    Skype: louis.rilling Batiment Germanium
    Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes 35700 Rennes
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