On 22/03/2016 12:59, Cornelia Huck wrote: >> > They can be fixed with just an extra object_ref/object_unref. >> > >> > I didn't understand that Tu Bo also needed the BH fix, and with that >> > information it makes sense. Passing the assign value ensures that >> > ioeventfd remains always assigned. With the CPU threads out of the >> > picture, the BH becomes enough to make everything thread-safe. > Yes, this makes sense. > > Might we still have a hole somewhere in dataplane teardown? Probably > not, from reading the code, even if it runs in cpu thread context.
The bug arises when the main thread sets started = true, a CPU thread comes along while the ioeventfd is reset, and as soon as the BQL is released by the main thread the CPU thread thinks it is a dataplane thread. This does horrible things to non-reentrant code. For stop we should be safe because the CPU thread is the one that sets started = false. IOW, we should be safe as long as the ioeventfd is never unassigned (your fix) _and_ we ensure serialization between threads that touch dataplane_started (Fam's fix). Paolo
