Re: [PATCH v2 11/22] migration/savevm: don't worry if bitmap migration postcopy failed

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Vladimir Sementsov-Ogievskiy (vsementsov@virtuozzo.com) wrote:
> First, if only bitmaps postcopy enabled (not ram postcopy)
> postcopy_pause_incoming crashes on assertion assert(mis->to_src_file).
> 
> And anyway, bitmaps postcopy is not prepared to be somehow recovered.
> The original idea instead is that if bitmaps postcopy failed, we just
> loss some bitmaps, which is not critical. So, on failure we just need
> to remove unfinished bitmaps and guest should continue execution on
> destination.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/savevm.c | 37 ++++++++++++++++++++++++++++++++-----
>  1 file changed, 32 insertions(+), 5 deletions(-)
> 
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 1d4220ece8..7e9dd58ccb 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -1812,6 +1812,9 @@ static void *postcopy_ram_listen_thread(void *opaque)
>      MigrationIncomingState *mis = migration_incoming_get_current();
>      QEMUFile *f = mis->from_src_file;
>      int load_res;
> +    MigrationState *migr = migrate_get_current();
> +
> +    object_ref(OBJECT(migr));
>  
>      migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
>                                     MIGRATION_STATUS_POSTCOPY_ACTIVE);
> @@ -1838,11 +1841,24 @@ static void *postcopy_ram_listen_thread(void *opaque)
>  
>      trace_postcopy_ram_listen_thread_exit();
>      if (load_res < 0) {
> -        error_report("%s: loadvm failed: %d", __func__, load_res);
>          qemu_file_set_error(f, load_res);
> -        migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_ACTIVE,
> -                                       MIGRATION_STATUS_FAILED);
> -    } else {
> +        dirty_bitmap_mig_cancel_incoming();
> +        if (postcopy_state_get() == POSTCOPY_INCOMING_RUNNING &&
> +            !migrate_postcopy_ram() && migrate_dirty_bitmaps())
> +        {
> +            error_report("%s: loadvm failed during postcopy: %d. All state is "
> +                         "migrated except for dirty bitmaps. Some dirty "
> +                         "bitmaps may be lost, and present migrated dirty "
> +                         "bitmaps are correctly migrated and valid.",
> +                         __func__, load_res);
> +            load_res = 0; /* prevent further exit() */
> +        } else {
> +            error_report("%s: loadvm failed: %d", __func__, load_res);
> +            migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_ACTIVE,
> +                                           MIGRATION_STATUS_FAILED);
> +        }
> +    }
> +    if (load_res >= 0) {
>          /*
>           * This looks good, but it's possible that the device loading in the
>           * main thread hasn't finished yet, and so we might not be in 'RUN'
> @@ -1878,6 +1894,8 @@ static void *postcopy_ram_listen_thread(void *opaque)
>      mis->have_listen_thread = false;
>      postcopy_state_set(POSTCOPY_INCOMING_END);
>  
> +    object_unref(OBJECT(migr));
> +
>      return NULL;
>  }
>  
> @@ -2429,6 +2447,8 @@ static bool postcopy_pause_incoming(MigrationIncomingState *mis)
>  {
>      trace_postcopy_pause_incoming();
>  
> +    assert(migrate_postcopy_ram());
> +
>      /* Clear the triggered bit to allow one recovery */
>      mis->postcopy_recover_triggered = false;
>  
> @@ -2513,15 +2533,22 @@ out:
>      if (ret < 0) {
>          qemu_file_set_error(f, ret);
>  
> +        /* Cancel bitmaps incoming regardless of recovery */
> +        dirty_bitmap_mig_cancel_incoming();
> +
>          /*
>           * If we are during an active postcopy, then we pause instead
>           * of bail out to at least keep the VM's dirty data.  Note
>           * that POSTCOPY_INCOMING_LISTENING stage is still not enough,
>           * during which we're still receiving device states and we
>           * still haven't yet started the VM on destination.
> +         *
> +         * Only RAM postcopy supports recovery. Still, if RAM postcopy is
> +         * enabled, canceled bitmaps postcopy will not affect RAM postcopy
> +         * recovering.
>           */
>          if (postcopy_state_get() == POSTCOPY_INCOMING_RUNNING &&
> -            postcopy_pause_incoming(mis)) {
> +            migrate_postcopy_ram() && postcopy_pause_incoming(mis)) {
>              /* Reset f to point to the newly created channel */
>              f = mis->from_src_file;
>              goto retry;
> -- 
> 2.21.0
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK