Re: [PATCHv7 2/3] gnttab: refactor locking for scalability

[David Vrabel <david.vrabel@citrix.com>]

On 30/04/15 15:34, Tim Deegan wrote:
> 
> OK, so here we hold rd->grant_table->lock and act->lock (which is in
> the rd table) and are going to acquire lgt->maptrack_lock in mapcount().
> 
> That means we can't ever have a path holding domA's maptrack lock that
> acquires domB's gt lock or one of domB's act->locks.  I think that's
> OK because after this patch the only paths left that hold the maptrack
> lock can't acquire anything except an act->lock of the same domain.
> Do I understand that correctly?
> 
> Also: because mapcount() itself doesn't take any act->lock, there's no
> path that holds two act->locks at the same time?

Um. I think it's easier if we just say you cannot take another lock
while holding a maptrack_lock since that's currently the case.

David