From: mleitner@xxxxxxxxxx
Date: Thu, 11 Jun 2015 11:30:46 -0300
> Attempts to circumvent this lock invertion with RCU and/or list splicing
> were unsuccessful, as they led to more and more code to handle it
> properly.
>
> Back when Hannes started reviewing the patches, he had asked if I
> couldn't take the lock earlier during the socket destruction. I had said
> no because sctp_destroy_sock() is called with socket lock already held
> on sctp_close_sock() and such would not be possible to handle on error
> handling situations like when sctp_init_sock() fails and
> sctp_destroy_sock() is called right after that.
>
> But if we take care that nothing fails after initializing asconf on
> sctp_init_sock(), this is possible, and less complicated than my RCU and
> list splicing attempts.
This is definitely a cleaner/simpler fix, but:
> @@ -1528,7 +1528,10 @@ static void sctp_close(struct sock *sk, long timeout)
>
> /* Supposedly, no process has access to the socket, but
> * the net layers still may.
> + * Also, sctp_destroy_sock() needs to be called with addr_wq_lock
> + * held and that should be grabbed before socket lock.
> */
> + spin_lock_bh(&net->sctp.addr_wq_lock);
> local_bh_disable();
> bh_lock_sock(sk);
>
> @@ -1540,6 +1543,7 @@ static void sctp_close(struct sock *sk, long timeout)
>
> bh_unlock_sock(sk);
> local_bh_enable();
> + spin_unlock_bh(&net->sctp.addr_wq_lock);
>
> sock_put(sk);
>
The local_bh_{enable,disable}() now appear to be superfluous and thus
can be removed.
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