On Fri, Mar 15, 2024 at 03:21:27PM +0100, Cédric Le Goater wrote:
> On 3/15/24 13:20, Cédric Le Goater wrote:
> > On 3/15/24 12:01, Peter Xu wrote:
> > > On Fri, Mar 15, 2024 at 11:17:45AM +0100, Cédric Le Goater wrote:
> > > > > migrate_set_state is also unintuitive because it ignores invalid state
> > > > > transitions and we've been using that property to deal with special
> > > > > states such as POSTCOPY_PAUSED and FAILED:
> > > > >
> > > > > - After the migration goes into POSTCOPY_PAUSED, the resumed
> > > > > migration's
> > > > > migrate_init() will try to set the state NONE->SETUP, which is not
> > > > > valid.
> > > > >
> > > > > - After save_setup fails, the migration goes into FAILED, but
> > > > > wait_unplug
> > > > > will try to transition SETUP->ACTIVE, which is also not valid.
> > > > >
> > > >
> > > > I am not sure I understand what the plan is. Both solutions are
> > > > problematic
> > > > regarding the state transitions.
> > > >
> > > > Should we consider that waiting for failover devices to unplug is an
> > > > internal
> > > > step of the SETUP phase not transitioning to ACTIVE ?
> > >
> > > If to unblock this series, IIUC the simplest solution is to do what
> > > Fabiano
> > > suggested, that we move qemu_savevm_wait_unplug() to be before the check
> > > of
> > > setup() ret.
> >
> > The simplest is IMHO moving qemu_savevm_wait_unplug() before
> > qemu_savevm_state_setup() and leave patch 10 is unchanged. See
> > below the extra patch. It looks much cleaner than what we have
> > today.
> >
> > > In that case, the state change in qemu_savevm_wait_unplug()
> > > should be benign and we should see a super small window it became ACTIVE
> > > but then it should be FAILED (and IIUC the patch itself will need to use
> > > ACTIVE as "old_state", not SETUP anymore).
> >
> > OK. I will give it a try to compare.
>
> Here's the alternative solution. SETUP state failures are handled after
> transitioning to ACTIVE state, which is unfortunate but probably harmless.
> I guess it's OK.
This also looks good to me, thanks.
One trivial early comment is in this case we can introduce a helper to
cover both setup() calls and UNPLUG waits and dedup the two paths.
>
> Thanks,
>
> C.
>
>
>
> Signed-off-by: Cédric Le Goater <c...@redhat.com>
> ---
> migration/savevm.h | 2 +-
> migration/migration.c | 29 +++++++++++++++++++++++++++--
> migration/savevm.c | 26 +++++++++++++++-----------
> 3 files changed, 43 insertions(+), 14 deletions(-)
>
> diff --git a/migration/savevm.h b/migration/savevm.h
> index
> 74669733dd63a080b765866c703234a5c4939223..9ec96a995c93a42aad621595f0ed58596c532328
> 100644
> --- a/migration/savevm.h
> +++ b/migration/savevm.h
> @@ -32,7 +32,7 @@
> bool qemu_savevm_state_blocked(Error **errp);
> void qemu_savevm_non_migratable_list(strList **reasons);
> int qemu_savevm_state_prepare(Error **errp);
> -void qemu_savevm_state_setup(QEMUFile *f);
> +int qemu_savevm_state_setup(QEMUFile *f, Error **errp);
> bool qemu_savevm_state_guest_unplug_pending(void);
> int qemu_savevm_state_resume_prepare(MigrationState *s);
> void qemu_savevm_state_header(QEMUFile *f);
> diff --git a/migration/migration.c b/migration/migration.c
> index
> 644e073b7dcc70cb2bdaa9c975ba478952465ff4..0704ad6226df61f2f15bd81a2897f9946d601ca7
> 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -3427,6 +3427,8 @@ static void *migration_thread(void *opaque)
> int64_t setup_start = qemu_clock_get_ms(QEMU_CLOCK_HOST);
> MigThrError thr_error;
> bool urgent = false;
> + Error *local_err = NULL;
> + int ret;
> thread = migration_threads_add("live_migration", qemu_get_thread_id());
> @@ -3470,12 +3472,24 @@ static void *migration_thread(void *opaque)
> }
> bql_lock();
> - qemu_savevm_state_setup(s->to_dst_file);
> + ret = qemu_savevm_state_setup(s->to_dst_file, &local_err);
> bql_unlock();
> qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
> MIGRATION_STATUS_ACTIVE);
> + /*
> + * Handle SETUP failures after waiting for virtio-net-failover
> + * devices to unplug. This to preserve migration state transitions.
> + */
> + if (ret) {
> + migrate_set_error(s, local_err);
> + error_free(local_err);
> + migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
> + MIGRATION_STATUS_FAILED);
> + goto out;
> + }
> +
> s->setup_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) - setup_start;
> trace_migration_thread_setup_complete();
> @@ -3549,6 +3563,8 @@ static void *bg_migration_thread(void *opaque)
> MigThrError thr_error;
> QEMUFile *fb;
> bool early_fail = true;
> + Error *local_err = NULL;
> + int ret;
> rcu_register_thread();
> object_ref(OBJECT(s));
> @@ -3582,12 +3598,20 @@ static void *bg_migration_thread(void *opaque)
> bql_lock();
> qemu_savevm_state_header(s->to_dst_file);
> - qemu_savevm_state_setup(s->to_dst_file);
> + ret = qemu_savevm_state_setup(s->to_dst_file, &local_err);
> bql_unlock();
> qemu_savevm_wait_unplug(s, MIGRATION_STATUS_SETUP,
> MIGRATION_STATUS_ACTIVE);
> + if (ret) {
> + migrate_set_error(s, local_err);
> + error_free(local_err);
> + migrate_set_state(&s->state, MIGRATION_STATUS_ACTIVE,
> + MIGRATION_STATUS_FAILED);
> + goto fail_setup;
> + }
> +
> s->setup_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) - setup_start;
> trace_migration_thread_setup_complete();
> @@ -3656,6 +3680,7 @@ fail:
> bql_unlock();
> }
> +fail_setup:
> bg_migration_iteration_finish(s);
> qemu_fclose(fb);
> diff --git a/migration/savevm.c b/migration/savevm.c
> index
> 1a7b5cb78a912c36ae16db703afc90ef2906b61f..0eb94e61f888adba2c0732c2cb701b110814c455
> 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1310,11 +1310,11 @@ int qemu_savevm_state_prepare(Error **errp)
> return 0;
> }
> -void qemu_savevm_state_setup(QEMUFile *f)
> +int qemu_savevm_state_setup(QEMUFile *f, Error **errp)
> {
> + ERRP_GUARD();
> MigrationState *ms = migrate_get_current();
> SaveStateEntry *se;
> - Error *local_err = NULL;
> int ret = 0;
> json_writer_int64(ms->vmdesc, "page_size", qemu_target_page_size());
> @@ -1323,10 +1323,9 @@ void qemu_savevm_state_setup(QEMUFile *f)
> trace_savevm_state_setup();
> QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
> if (se->vmsd && se->vmsd->early_setup) {
> - ret = vmstate_save(f, se, ms->vmdesc, &local_err);
> + ret = vmstate_save(f, se, ms->vmdesc, errp);
> if (ret) {
> - migrate_set_error(ms, local_err);
> - error_report_err(local_err);
> + migrate_set_error(ms, *errp);
> qemu_file_set_error(f, ret);
> break;
> }
> @@ -1346,18 +1345,19 @@ void qemu_savevm_state_setup(QEMUFile *f)
> ret = se->ops->save_setup(f, se->opaque);
> save_section_footer(f, se);
> if (ret < 0) {
> + error_setg(errp, "failed to setup SaveStateEntry with id(name): "
> + "%d(%s): %d", se->section_id, se->idstr, ret);
> qemu_file_set_error(f, ret);
> break;
> }
> }
> if (ret) {
> - return;
> + return ret;
> }
> - if (precopy_notify(PRECOPY_NOTIFY_SETUP, &local_err)) {
> - error_report_err(local_err);
> - }
> + /* TODO: Should we check that errp is set in case of failure ? */
> + return precopy_notify(PRECOPY_NOTIFY_SETUP, errp);
> }
> int qemu_savevm_state_resume_prepare(MigrationState *s)
> @@ -1725,7 +1725,10 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
> ms->to_dst_file = f;
> qemu_savevm_state_header(f);
> - qemu_savevm_state_setup(f);
> + ret = qemu_savevm_state_setup(f, errp);
> + if (ret) {
> + goto cleanup;
> + }
> while (qemu_file_get_error(f) == 0) {
> if (qemu_savevm_state_iterate(f, false) > 0) {
> @@ -1738,10 +1741,11 @@ static int qemu_savevm_state(QEMUFile *f, Error
> **errp)
> qemu_savevm_state_complete_precopy(f, false, false);
> ret = qemu_file_get_error(f);
> }
> - qemu_savevm_state_cleanup();
> if (ret != 0) {
> error_setg_errno(errp, -ret, "Error while writing VM state");
> }
> +cleanup:
> + qemu_savevm_state_cleanup();
> if (ret != 0) {
> status = MIGRATION_STATUS_FAILED;
> --
> 2.44.0
>
>
--
Peter Xu
