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    SubjectRe: [PATCH 1/2] rcu: add rcu_access_pointer and rcu_dereference_protect
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    Le mercredi 07 avril 2010 à 17:19 +0100, David Howells a écrit :

    > what is the value of sk->sk_wmem_alloc to the lock context of sk->sk_filter?
    > Why would lockdep be interested in sk_wmem_alloc?
    >
    > Surely, the assertion that the value of sk->sk_filter is related to
    > sk_wmem_alloc being 0 is independent of the need to dereference sk_filter for
    > RCU purposes. So why are these being combined?

    Because when sk->sk_filter is eventually written by some thread, this
    thread _must_ own a reference on the socket, that is sk_wmem_alloc > 0

    So when reading sk->sk_filter, the general condition is :
    - We own the rcu lock
    - But on the particular case of __sk_free(),
    we owned the very last reference to sk (we are going to kfree it), so
    nobody can possibly change sk->sk_filter under us.



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