Am 08.04.2021 um 11:21 hat Markus Armbruster geschrieben: > 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?
This is something that the responsible maintainer needs to decide. If it helps you with the decision, and if I understand correctly, it is a regression from 5.1, but was already broken in 5.2. Kevin
