[openib-general] APM support in openib stack

[Sean Hefty]

Venkatesh Babu wrote:
> The patch for ib_sa_serv_notice_hdlr() handles multiple callers 
> registering for the same event by maintaining a linked list of callback 
> handlers. So I didn't think that the multiple user count was necessary. 
> The actual registration with the MAD layer happens only when the ib_sa 
> module is initialized and unregistered when it is unloaded.

Since MADs can be delivered / processed out of order, there's a race if one user 
unregisters for events at the same time another user tries to register.  The 
second user can be left unregistered.  Requests to the SA for the same event 
must be serialized to ensure that we are left in the proper registration state.

The problem becomes more complex when a user cancels their request while it's 
still being processed.

- Sean