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    SubjectRe: [RFC] Refcounting of objects part of a lockfree collection
    On Wed, Jul 14, 2004 at 12:07:00AM -0700, Greg KH wrote:
    > On Wed, Jul 14, 2004 at 10:23:50AM +0530, Ravikiran G Thirumalai wrote:
    > >
    > > The attatched patch provides infrastructure for refcounting of objects
    > > in a rcu protected collection.
    >
    > This is really close to the kref implementation. Why not just use that
    > instead?

    Well, the kref has the same get/put race if used in a lock-free
    look-up. When you do a kref_get() it is assumed that another
    cpu will not see a 1-to-0 transition of the reference count.
    If that indeed happens, ->release() will get invoked more
    than once for that object which is bad. Kiran's patch actually
    solves this fundamental lock-free ref-counting problem.

    The other issue is that there are many refcounted data structures
    like dentry, dst_entry, file etc. that do not use kref. If everybody
    were to use kref, we could possibly apply Kiran's lock-free extensions
    to kref itself and be done with it. Until then, we need the lock-free
    refcounting support from non-kref refcounting objects.

    Thanks
    Dipankar
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