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SubjectRe: Q: sock output serialization

> I guess I╢d also need to call lock_sock() from sendmsg(). And before
> calling x25_kick from socket input path, I╢d need to verify that
> sk->lock.users is zero. If sk->lock.users was !=0, I╢d need some atomic
> variable anyway in order to defer the kick.

In input path you have a packet. Add it to backlog and processing
will be resumed after lock is released. Compare with tcp.

> serializing the kick. Well, maybe my solution could still be simplified
> (maybe some test_and_set/clear_bit() magic could achieve the same).

Being legal in principle, using non-standard serialization primitives
is seriously deprecated. It is impossible to maintain. In you case,
it is even not evident that it does not lose events with smp.

> - introduce a protocol-global spinlock and protect protocol-global
> critical section by spin_lock_bh() instead of cli()

Why? It is not required. There are no reasons to protect protocol
as whole, if sockets are protected.

> - protect all sock proto_ops methods by lock_sock()


> - when bh functions need to be protected from sk state change, they
> need to aquire bh_lock_sock()

And check for sk->lock.users. If it is not zero, operation is deferred.

> - before bh (timer) function change sk state, they need to aquire
> bh_lock_sock and verify, that sk->lock.users!=0


> - remove the SOCKOPS_WRAPPED() macro from the proto_ops

Yes. And finally announce protocol to be SMP aware setting data
field of packet_type to 1.

> Can NET_TX_SOFTIRQ be prempted by NET_RX_SOFTIRQ or timer?

It cannot be preempted, but it is not very essential, because
all they can run in parallel on different cpus.

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