Re: [PATCH v2] vfs: Don't exchange "short" filenames unconditionally.

On Thu, Sep 25, 2014 at 05:46:01AM +0100, Al Viro wrote:

I really wonder if it's possible to get d_rehash() hitting the victim of
(non-exchange) __d_move().  _Then_ this patch (as well as the historical
behaviour it restores, all way back to 2.5, if not 2.3) would, indeed,
be buggy.

More fun: what's going on in ceph_handle_notrace_create()?  AFAICS, this
        struct dentry *result = ceph_lookup(dir, dentry, 0);

        if (result && !IS_ERR(result)) {
                /*
                 * We created the item, then did a lookup, and found
                 * it was already linked to another inode we already
                 * had in our cache (and thus got spliced).  Link our
                 * dentry to that inode, but don't hash it, just in  
                 * case the VFS wants to dereference it.
                 */
                BUG_ON(!result->d_inode);
                d_instantiate(dentry, result->d_inode);
                return 0;
        }
is bogus.  What will happen if server goes nuts and that existing alias picked
by lookup turns out to be a directory?  And while we are at it, what's to
prevent a leak if we ever hit that codepath, directory or no directory?
Sage?