Re: synchronization between bottom half and user context

[jamal <hadi@xxxxxxxxxx>]

On Tue, 3 Dec 2002, Ronghua Zhang wrote:

> Can someone tell me when lock should be used to synchronize bh and user
> context?
>
> For examle: in tcp_accept(), lock_sock() is called to avoid any change
> made by net_bh during its operation. But if tcp_accept() is called, it's
> impossilbe that net_bh is also executing. (i think this is true for UP,
> what about SMP?), then why need lock_sock()?
>

to serialize packets towards the socket; The linux network stack
is threaded, you can have upto n packets to the same socket coming up the
stack in parallel on an n-SMP machine; think of that and the fact that TCP
data must be sequenced.

cheers,
jamal