Am 22.03.2021 um 16:40 hat Stefan Reiter geschrieben: > The QMP dispatcher coroutine holds the qmp_queue_lock over a yield > point, where it expects to be rescheduled from the main context. If a > CHR_EVENT_CLOSED event is received just then, it can race and block the > main thread on the mutex in monitor_qmp_cleanup_queue_and_resume. > > monitor_resume does not need to be called from main context, so we can > call it immediately after popping a request from the queue, which allows > us to drop the qmp_queue_lock mutex before yielding. > > Suggested-by: Wolfgang Bumiller <w.bumil...@proxmox.com> > Signed-off-by: Stefan Reiter <s.rei...@proxmox.com> > --- > v2: > * different approach: move everything that needs the qmp_queue_lock mutex > before > the yield point, instead of moving the event handling to a different context
The interesting new case here seems to be that new requests could be queued and the dispatcher coroutine could be kicked before yielding. This is safe because &qmp_dispatcher_co_busy is accessed with atomics on both sides. The important part is just that the first (conditional) yield stays first, so that the aio_co_wake() in handle_qmp_command() won't reenter the coroutine while it is expecting to be reentered from somewhere else. This is still the case after the patch. Reviewed-by: Kevin Wolf <kw...@redhat.com>
