On Thu, Apr 04, 2024 at 06:05:50PM +0800, Wei Wang wrote: > Before loading the guest states, ensure that the preempt channel has been > ready to use, as some of the states (e.g. via virtio_load) might trigger > page faults that will be handled through the preempt channel. So yield to > the main thread in the case that the channel create event has been > dispatched. > > Originally-by: Lei Wang <lei4.w...@intel.com> > Link: > https://lore.kernel.org/all/9aa5d1be-7801-40dd-83fd-f7e041ced...@intel.com/T/ > Suggested-by: Peter Xu <pet...@redhat.com> > Signed-off-by: Lei Wang <lei4.w...@intel.com> > Signed-off-by: Wei Wang <wei.w.w...@intel.com> > --- > migration/savevm.c | 17 +++++++++++++++++ > 1 file changed, 17 insertions(+) > > diff --git a/migration/savevm.c b/migration/savevm.c > index 388d7af7cd..fbc9f2bdd4 100644 > --- a/migration/savevm.c > +++ b/migration/savevm.c > @@ -2342,6 +2342,23 @@ static int > loadvm_handle_cmd_packaged(MigrationIncomingState *mis) > > QEMUFile *packf = qemu_file_new_input(QIO_CHANNEL(bioc)); > > + /* > + * Before loading the guest states, ensure that the preempt channel has > + * been ready to use, as some of the states (e.g. via virtio_load) might > + * trigger page faults that will be handled through the preempt channel. > + * So yield to the main thread in the case that the channel create event > + * has been dispatched. > + */ > + do { > + if (!migrate_postcopy_preempt() || !qemu_in_coroutine() || > + mis->postcopy_qemufile_dst) { > + break; > + } > + > + aio_co_schedule(qemu_get_current_aio_context(), > qemu_coroutine_self()); > + qemu_coroutine_yield(); > + } while (!qemu_sem_timedwait(&mis->postcopy_qemufile_dst_done, 1));
I think we need s/!// here, so the same mistake I made? I think we need to rework the retval of qemu_sem_timedwait() at some point later.. Besides, this patch kept the sem_wait() in postcopy_preempt_thread() so it will wait() on this sem again. If this qemu_sem_timedwait() accidentally consumed the sem count then I think the other thread can hang forever? That's why I put the wait before creation of the preempt thread (in postcopy_ram_incoming_setup()), as we can only consume the sem once, so we must prepare the qemufile when the thread is created. Thanks, > + > ret = qemu_loadvm_state_main(packf, mis); > trace_loadvm_handle_cmd_packaged_main(ret); > qemu_fclose(packf); > -- > 2.27.0 > -- Peter Xu
