Re: [Qemu-devel] [PATCH RFC v6 6/7] migration: fix some error handling

[Dr. David Alan Gilbert]

* Fei Li (address@hidden) wrote:
> Add error handling for qemu_ram_foreach_migratable_block() when
> it fails.
> 
> Always call migrate_set_error() to set the error state without relying
> on whether multifd_save_cleanup() succeeds. As the passed &local_err
> is never used in multifd_save_cleanup(), remove it.
> 
> Signed-off-by: Fei Li <address@hidden>
> ---
>  migration/migration.c    | 5 +----
>  migration/postcopy-ram.c | 3 +++
>  migration/ram.c          | 7 +++----
>  migration/ram.h          | 2 +-
>  4 files changed, 8 insertions(+), 9 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 87dfc7374f..3b8b7ab4f9 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1377,7 +1377,6 @@ static void migrate_fd_cleanup(void *opaque)
>      qemu_savevm_state_cleanup();
>  
>      if (s->to_dst_file) {
> -        Error *local_err = NULL;
>          QEMUFile *tmp;
>  
>          trace_migrate_fd_cleanup();
> @@ -1388,9 +1387,7 @@ static void migrate_fd_cleanup(void *opaque)
>          }
>          qemu_mutex_lock_iothread();
>  
> -        if (multifd_save_cleanup(&local_err) != 0) {
> -            error_report_err(local_err);
> -        }
> +        multifd_save_cleanup();
>          qemu_mutex_lock(&s->qemu_file_lock);
>          tmp = s->to_dst_file;
>          s->to_dst_file = NULL;
> diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> index e5c02a32c5..4ca2bc02b3 100644
> --- a/migration/postcopy-ram.c
> +++ b/migration/postcopy-ram.c
> @@ -1117,6 +1117,9 @@ int postcopy_ram_enable_notify(MigrationIncomingState 
> *mis)
>  
>      /* Mark so that we get notified of accesses to unwritten areas */
>      if (qemu_ram_foreach_migratable_block(ram_block_enable_notify, mis)) {
> +        error_report("ram_block_enable_notify failed");
> +        close(mis->userfault_event_fd);
> +        close(mis->userfault_fd);

I don't think these close() calls are safe.  This code is just after
starting the fault thread, and the fault thread has a poll() call on
these fd's, so we can't close them until we've instructed that thread
to exit.

We should fall out through postcopy_ram_incoming_cleanup, and because
the thread exists it should do a notify to the thread, a join and then
only later do the close calls.

Dave

>          return -1;
>      }
>  
> diff --git a/migration/ram.c b/migration/ram.c
> index 8f03afe228..57cb1bee3d 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -922,7 +922,7 @@ static void multifd_send_terminate_threads(Error *err)
>      }
>  }
>  
> -int multifd_save_cleanup(Error **errp)
> +int multifd_save_cleanup(void)
>  {
>      int i;
>      int ret = 0;
> @@ -1082,9 +1082,8 @@ static void multifd_new_send_channel_async(QIOTask 
> *task, gpointer opaque)
>  
>      if (qio_task_propagate_error(task, &local_err)) {
>          migrate_set_state(&s->state, s->state, MIGRATION_STATUS_FAILED);
> -        if (multifd_save_cleanup(&local_err) != 0) {
> -            migrate_set_error(migrate_get_current(), local_err);
> -        }
> +        multifd_save_cleanup();
> +        migrate_set_error(migrate_get_current(), local_err);
>      } else {
>          p->c = QIO_CHANNEL(sioc);
>          qio_channel_set_delay(p->c, false);
> diff --git a/migration/ram.h b/migration/ram.h
> index 046d3074be..0d1215209e 100644
> --- a/migration/ram.h
> +++ b/migration/ram.h
> @@ -43,7 +43,7 @@ uint64_t ram_bytes_remaining(void);
>  uint64_t ram_bytes_total(void);
>  
>  int multifd_save_setup(void);
> -int multifd_save_cleanup(Error **errp);
> +int multifd_save_cleanup(void);
>  int multifd_load_setup(void);
>  int multifd_load_cleanup(Error **errp);
>  bool multifd_recv_all_channels_created(void);
> -- 
> 2.13.7
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK