Re: [Qemu-devel] [RFC PATCH v4 15/15] slirp: use lock to protect the slirp_instances

[Paolo Bonzini]

> grep'ing for slirp_instances points to more spots that work with that
> list (QTAILQ_FOREACH, QTAILQ_EMPTY, ...). So the same question here:
> What are the usage rules? When do I _not_ need it when touching the list
> of instances, and why?
> 
> Well, I started reading at the top, but there are more lock-adding
> patches in this series. And the more locks we have, the higher the
> probability of ABBA gets. Therefore, please document from the beginning
> the lock order rules that shall prevent it (which may also be "never
> take other locks while holding this one" or "never hold other locks when
> taking this one").

Yeah, the only sane ordering rules should be "hold nothing or just
the BQL when taking this one".  Everything else needs a very good
justification...

Paolo