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

[Peter Xu <peterx@redhat.com>]

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);
> -}
> -
>  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