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    SubjectRe: [git pull] vfs and fs fixes
    On Tue, Apr 17, 2012 at 03:08:26PM -0700, Linus Torvalds wrote:
    > On Tue, Apr 17, 2012 at 2:14 PM, J. Bruce Fields <bfields@fieldses.org> wrote:
    > > On Tue, Apr 17, 2012 at 07:28:26PM +0100, Al Viro wrote:>
    > > Maybe instead I could continue using the i_mutex but handle rename some
    > > other way; e.g. in delegation code:
    > >
    > >        if (!mutex_trylock(inode->i_mutex))
    > >                return -EAGAIN;
    > >        if (atomic_read(inode->i_renames_in_progress))
    > >                return -EAGAIN;
    > >
    > > and add an
    > >
    > >        atomic_inc(inode->i_renames_in_progress);
    > >        atomic_dec(inode->i_renames_in_progress);
    > >
    > > pair around rename.
    >
    > Please don't make up your own locking. Plus it's broken anyway, since
    > a rename could come in directly after your atomic_read (and this is
    > *why* people shouldn't make up their own locks - they are invariably
    > broken).

    Doh, yes, sounds like a good rule. (I was misremembering some previous
    attempt at this--which admittedly may just have failed in some more
    complicated way.)

    --b.

    > > Or I could increment that counter for all the conflicting operations and
    > > rely on it instead of the i_mutex.  I was trying to avoid adding
    > > something like that (an inc, a dec, another error path) to every
    > > operation.  And hoping to avoid adding another field to struct inode.
    > > Oh well.
    >
    > We could just say that we can do a double inode lock, but then
    > standardize on the order. And the only sane order is comparing inode
    > pointers, not inode numbers like ext4 apparently does.
    >
    > With a standard order, I don't think it would be at all wrong to just
    > take the inode lock on rename.
    >
    > Linus
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