Re: [Qemu-devel] [PATCH v9 02/12] migration: Improve migration thread error handling

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

* Juan Quintela (quintela@redhat.com) wrote:
> We now report errors also when we finish migration, not only on info
> migrate.  We plan to use this error from several places, and we want
> the first error to happen to win, so we add an mutex to order it.
> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
>  migration/migration.c | 19 ++++++++++++++++---
>  migration/migration.h |  7 ++++++-
>  migration/tls.c       |  1 -
>  3 files changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 98429dc843..468f51cfa7 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1071,19 +1071,30 @@ static void migrate_fd_cleanup(void *opaque)
>                            MIGRATION_STATUS_CANCELLED);
>      }
>  
> +    if (s->error) {
> +        /* It is used on info migrate.  We can't free it */
> +        error_report_err(error_copy(s->error));
> +    }
>      notifier_list_notify(&migration_state_notifiers, s);
>      block_cleanup_parameters(s);
>  }
>  
> +void migrate_set_error(MigrationState *s, const Error *error)

If you find you need to resend this, please add a comment on this
function saying it takes a copy and it's upto the caller to free
the error they pass in.

Dave

> +{
> +    qemu_mutex_lock(&s->error_mutex);
> +    if (!s->error) {
> +        s->error = error_copy(error);
> +    }
> +    qemu_mutex_unlock(&s->error_mutex);
> +}
> +
>  void migrate_fd_error(MigrationState *s, const Error *error)
>  {
>      trace_migrate_fd_error(error_get_pretty(error));
>      assert(s->to_dst_file == NULL);
>      migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
>                        MIGRATION_STATUS_FAILED);
> -    if (!s->error) {
> -        s->error = error_copy(error);
> -    }
> +    migrate_set_error(s, error);
>      notifier_list_notify(&migration_state_notifiers, s);
>      block_cleanup_parameters(s);
>  }
> @@ -2355,6 +2366,7 @@ static void migration_instance_finalize(Object *obj)
>      MigrationState *ms = MIGRATION_OBJ(obj);
>      MigrationParameters *params = &ms->parameters;
>  
> +    qemu_mutex_destroy(&ms->error_mutex);
>      g_free(params->tls_hostname);
>      g_free(params->tls_creds);
>  }
> @@ -2367,6 +2379,7 @@ static void migration_instance_init(Object *obj)
>      ms->state = MIGRATION_STATUS_NONE;
>      ms->xbzrle_cache_size = DEFAULT_MIGRATE_CACHE_SIZE;
>      ms->mbps = -1;
> +    qemu_mutex_init(&ms->error_mutex);
>  
>      params->tls_hostname = g_strdup("");
>      params->tls_creds = g_strdup("");
> diff --git a/migration/migration.h b/migration/migration.h
> index b83cceadc4..51c0ac2e71 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -129,8 +129,12 @@ struct MigrationState
>      int64_t colo_checkpoint_time;
>      QEMUTimer *colo_delay_timer;
>  
> -    /* The last error that occurred */
> +    /* The first error that has occurred.
> +       We used the mutex to be able to return the 1st error message */
>      Error *error;
> +    /* mutex to protect errp */
> +    QemuMutex error_mutex;
> +
>      /* Do we have to clean up -b/-i from old migrate parameters */
>      /* This feature is deprecated and will be removed */
>      bool must_remove_block_options;
> @@ -159,6 +163,7 @@ bool  migration_has_all_channels(void);
>  
>  uint64_t migrate_max_downtime(void);
>  
> +void migrate_set_error(MigrationState *s, const Error *error);
>  void migrate_fd_error(MigrationState *s, const Error *error);
>  
>  void migrate_fd_connect(MigrationState *s);
> diff --git a/migration/tls.c b/migration/tls.c
> index 596e8790bd..026a008667 100644
> --- a/migration/tls.c
> +++ b/migration/tls.c
> @@ -119,7 +119,6 @@ static void migration_tls_outgoing_handshake(QIOTask *task,
>      if (qio_task_propagate_error(task, &err)) {
>          trace_migration_tls_outgoing_handshake_error(error_get_pretty(err));
>          migrate_fd_error(s, err);
> -        error_free(err);
>      } else {
>          trace_migration_tls_outgoing_handshake_complete();
>          migration_channel_connect(s, ioc, NULL);
> -- 
> 2.13.5
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK