Re: [PATCH V3 10/13] migration: stop vm for cpr

[Peter Xu]

On Thu, Feb 22, 2024 at 05:12:53PM +0800, Peter Xu wrote:
> On Wed, Feb 21, 2024 at 04:20:07PM -0500, Steven Sistare wrote:
> > On 2/20/2024 2:33 AM, Peter Xu wrote:
> > > On Thu, Feb 08, 2024 at 10:54:03AM -0800, Steve Sistare wrote:
> > >> When migration for cpr is initiated, stop the vm and set state
> > >> RUN_STATE_FINISH_MIGRATE before ram is saved.  This eliminates the
> > >> possibility of ram and device state being out of sync, and guarantees
> > >> that a guest in the suspended state remains suspended, because qmp_cont
> > >> rejects a cont command in the RUN_STATE_FINISH_MIGRATE state.
> > >>
> > >> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> > >> ---
> > >>  include/migration/misc.h |  1 +
> > >>  migration/migration.c    | 32 +++++++++++++++++++++++++-------
> > >>  2 files changed, 26 insertions(+), 7 deletions(-)
> > >>
> > >> diff --git a/include/migration/misc.h b/include/migration/misc.h
> > >> index 6dc234b..54c99a3 100644
> > >> --- a/include/migration/misc.h
> > >> +++ b/include/migration/misc.h
> > >> @@ -60,6 +60,7 @@ void migration_object_init(void);
> > >>  void migration_shutdown(void);
> > >>  bool migration_is_idle(void);
> > >>  bool migration_is_active(MigrationState *);
> > >> +bool migrate_mode_is_cpr(MigrationState *);
> > >>  
> > >>  typedef enum MigrationEventType {
> > >>      MIG_EVENT_PRECOPY_SETUP,
> > >> diff --git a/migration/migration.c b/migration/migration.c
> > >> index d1fce9e..fc5c587 100644
> > >> --- a/migration/migration.c
> > >> +++ b/migration/migration.c
> > >> @@ -1603,6 +1603,11 @@ bool migration_is_active(MigrationState *s)
> > >>              s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE);
> > >>  }
> > >>  
> > >> +bool migrate_mode_is_cpr(MigrationState *s)
> > >> +{
> > >> +    return s->parameters.mode == MIG_MODE_CPR_REBOOT;
> > >> +}
> > >> +
> > >>  int migrate_init(MigrationState *s, Error **errp)
> > >>  {
> > >>      int ret;
> > >> @@ -2651,13 +2656,14 @@ static int 
> > >> migration_completion_precopy(MigrationState *s,
> > >>      bql_lock();
> > >>      migration_downtime_start(s);
> > >>  
> > >> -    s->vm_old_state = runstate_get();
> > >> -    global_state_store();
> > >> -
> > >> -    ret = migration_stop_vm(RUN_STATE_FINISH_MIGRATE);
> > >> -    trace_migration_completion_vm_stop(ret);
> > >> -    if (ret < 0) {
> > >> -        goto out_unlock;
> > >> +    if (!migrate_mode_is_cpr(s)) {
> > >> +        s->vm_old_state = runstate_get();
> > >> +        global_state_store();
> > >> +        ret = migration_stop_vm(RUN_STATE_FINISH_MIGRATE);
> > >> +        trace_migration_completion_vm_stop(ret);
> > >> +        if (ret < 0) {
> > >> +            goto out_unlock;
> > >> +        }
> > >>      }
> > >>  
> > >>      ret = migration_maybe_pause(s, current_active_state,
> > >> @@ -3576,6 +3582,7 @@ void migrate_fd_connect(MigrationState *s, Error 
> > >> *error_in)
> > >>      Error *local_err = NULL;
> > >>      uint64_t rate_limit;
> > >>      bool resume = s->state == MIGRATION_STATUS_POSTCOPY_PAUSED;
> > >> +    int ret;
> > >>  
> > >>      /*
> > >>       * If there's a previous error, free it and prepare for another one.
> > >> @@ -3651,6 +3658,17 @@ void migrate_fd_connect(MigrationState *s, Error 
> > >> *error_in)
> > >>          goto fail;
> > >>      }
> > >>  
> > >> +    if (migrate_mode_is_cpr(s)) {
> > >> +        s->vm_old_state = runstate_get();
> > >> +        global_state_store();
> > >> +        ret = migration_stop_vm(RUN_STATE_FINISH_MIGRATE);
> > >> +        trace_migration_completion_vm_stop(ret);
> > >> +        if (ret < 0) {
> > >> +            error_setg(&local_err, "migration_stop_vm failed, error 
> > >> %d", -ret);
> > >> +            goto fail;
> > >> +        }
> > >> +    }
> > > 
> > > Could we have a helper function for the shared codes?
> > 
> > I propose to add code to migration_stop_vm to make it the helper.  Some 
> > call sites emit
> > more traces (via migration_stop_vm) as a result of my refactoring,
> 
> This should be fine.
> 
> > and postcopy start sets 
> > vm_old_state, which is not used thereafter in that path.  Those changes 
> > seem harmless to me.
> 
> Not only harmless, I think it was a bug to not set vm_old_state in
> postcopy_start()..  See:
> 
> https://issues.redhat.com/browse/RHEL-18061
> 
> I suspect that was the cause.
> 
> > Tell me what you think:
> 
> I'll have a closer look later, but so far it looks all good.
> 
> Thanks,
> 
> > 
> > -------------------------------------------------------
> > diff --git a/migration/migration.c b/migration/migration.c
> > index fc5c587..30d2b08 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -107,12 +107,6 @@ static int migration_maybe_pause(MigrationState *s,
> >  static void migrate_fd_cancel(MigrationState *s);
> >  static bool close_return_path_on_source(MigrationState *s);
> > 
> > -static void migration_downtime_start(MigrationState *s)
> > -{
> > -    trace_vmstate_downtime_checkpoint("src-downtime-start");
> > -    s->downtime_start = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> > -}

Ah.. one more thing: would you mind keep this helper even if it can be
squashed when sending formal patch?  I want to keep downtime start/end
super clear and paired as they're important hook points.  It should be
inlined anyway by the compiler.

> > -
> >  static void migration_downtime_end(MigrationState *s)
> >  {
> >      int64_t now = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> > @@ -161,11 +155,20 @@ static gint page_request_addr_cmp(gconstpointer ap, 
> > gconstpo
> >      return (a > b) - (a < b);
> >  }
> > 
> > -int migration_stop_vm(RunState state)
> > +static int migration_stop_vm(MigrationState *s, RunState state)
> >  {
> > -    int ret = vm_stop_force_state(state);
> > +    int ret;
> > +
> > +    trace_vmstate_downtime_checkpoint("src-downtime-start");
> > +    s->downtime_start = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> > +
> > +    s->vm_old_state = runstate_get();
> > +    global_state_store();
> > +
> > +    ret = vm_stop_force_state(state);
> > 
> >      trace_vmstate_downtime_checkpoint("src-vm-stopped");
> > +    trace_migration_completion_vm_stop(ret);
> > 
> >      return ret;
> >  }
> > @@ -2454,10 +2457,7 @@ static int postcopy_start(MigrationState *ms, Error 
> > **errp)
> >      bql_lock();
> >      trace_postcopy_start_set_run();
> > 
> > -    migration_downtime_start(ms);
> > -
> > -    global_state_store();
> > -    ret = migration_stop_vm(RUN_STATE_FINISH_MIGRATE);
> > +    ret = migration_stop_vm(ms, RUN_STATE_FINISH_MIGRATE);
> >      if (ret < 0) {
> >          goto fail;
> >      }
> > @@ -2654,13 +2654,9 @@ static int 
> > migration_completion_precopy(MigrationState *s,
> >      int ret;
> > 
> >      bql_lock();
> > -    migration_downtime_start(s);
> > 
> >      if (!migrate_mode_is_cpr(s)) {
> > -        s->vm_old_state = runstate_get();
> > -        global_state_store();
> > -        ret = migration_stop_vm(RUN_STATE_FINISH_MIGRATE);
> > -        trace_migration_completion_vm_stop(ret);
> > +        ret = migration_stop_vm(s, RUN_STATE_FINISH_MIGRATE);
> >          if (ret < 0) {
> >              goto out_unlock;
> >          }
> > @@ -3498,15 +3494,10 @@ static void *bg_migration_thread(void *opaque)
> >      s->setup_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) - setup_start;
> > 
> >      trace_migration_thread_setup_complete();
> > -    migration_downtime_start(s);
> > 
> >      bql_lock();
> > 
> > -    s->vm_old_state = runstate_get();
> > -
> > -    global_state_store();
> > -    /* Forcibly stop VM before saving state of vCPUs and devices */
> > -    if (migration_stop_vm(RUN_STATE_PAUSED)) {
> > +    if (migration_stop_vm(s, RUN_STATE_PAUSED)) {
> >          goto fail;
> >      }
> >      /*
> > @@ -3659,10 +3650,7 @@ void migrate_fd_connect(MigrationState *s, Error 
> > *error_in)
> >      }
> > 
> >      if (migrate_mode_is_cpr(s)) {
> > -        s->vm_old_state = runstate_get();
> > -        global_state_store();
> > -        ret = migration_stop_vm(RUN_STATE_FINISH_MIGRATE);
> > -        trace_migration_completion_vm_stop(ret);
> > +        ret = migration_stop_vm(s, RUN_STATE_FINISH_MIGRATE);
> >          if (ret < 0) {
> >              error_setg(&local_err, "migration_stop_vm failed, error %d", 
> > -ret);
> >              goto fail;
> > diff --git a/migration/migration.h b/migration/migration.h
> > index aef8afb..65c0b61 100644
> > --- a/migration/migration.h
> > +++ b/migration/migration.h
> > @@ -541,6 +541,4 @@ int migration_rp_wait(MigrationState *s);
> >   */
> >  void migration_rp_kick(MigrationState *s);
> > 
> > -int migration_stop_vm(RunState state);
> > -
> >  #endif
> > -------------------------------------------------------
> > 
> > - Steve
> > 
> 
> -- 
> Peter Xu

-- 
Peter Xu