Messages in this thread | | | Subject | Re: [PATCH 1/2] rcu: add rcu_access_pointer and rcu_dereference_protect | From | Eric Dumazet <> | Date | Wed, 07 Apr 2010 18:35:38 +0200 |
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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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