Kevin Wolf <kw...@redhat.com> writes: > 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>
Thanks for saving me from an ugly review headache. Should this go into 6.0?
