synchronization between bottom half and user context

[Ronghua Zhang <rz5b@xxxxxxxxxxxxxxx>]

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()?

ronghua