Re: [PATCH v2 19/23] migration/multifd: Cleanup multifd_save_cleanup()

[Fabiano Rosas <farosas@suse.de>]

peterx@redhat.com writes:

> From: Peter Xu <peterx@redhat.com>
>
> Shrink the function by moving relevant works into helpers: move the thread
> join()s into multifd_send_terminate_threads(), then create two more helpers
> to cover channel/state cleanups.
>
> Add a TODO entry for the thread terminate process because p->running is
> still buggy.  We need to fix it at some point but not yet covered.
>
> Suggested-by: Fabiano Rosas <farosas@suse.de>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Fabiano Rosas <farosas@suse.de>

minor comment below

> ---
>  migration/multifd.c | 91 +++++++++++++++++++++++++++++----------------
>  1 file changed, 59 insertions(+), 32 deletions(-)
>
> diff --git a/migration/multifd.c b/migration/multifd.c
> index 4ab8e6eff2..4cb0d2cc17 100644
> --- a/migration/multifd.c
> +++ b/migration/multifd.c
> @@ -593,6 +593,11 @@ static void multifd_send_terminate_threads(void)
>       * always set it.
>       */
>      qatomic_set(&multifd_send_state->exiting, 1);
> +
> +    /*
> +     * Firstly, kick all threads out; no matter whether they are just idle,
> +     * or blocked in an IO system call.
> +     */
>      for (i = 0; i < migrate_multifd_channels(); i++) {
>          MultiFDSendParams *p = &multifd_send_state->params[i];
>  
> @@ -601,6 +606,21 @@ static void multifd_send_terminate_threads(void)
>              qio_channel_shutdown(p->c, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
>          }
>      }
> +
> +    /*
> +     * Finally recycle all the threads.
> +     *
> +     * TODO: p->running is still buggy, e.g. we can reach here without the
> +     * corresponding multifd_new_send_channel_async() get invoked yet,
> +     * then a new thread can even be created after this function returns.
> +     */

Series on the list:

https://lore.kernel.org/r/20240202191128.1901-1-farosas@suse.de

> +    for (i = 0; i < migrate_multifd_channels(); i++) {
> +        MultiFDSendParams *p = &multifd_send_state->params[i];
> +
> +        if (p->running) {
> +            qemu_thread_join(&p->thread);
> +        }
> +    }
>  }
>  
>  static int multifd_send_channel_destroy(QIOChannel *send)
> @@ -608,6 +628,41 @@ static int multifd_send_channel_destroy(QIOChannel *send)
>      return socket_send_channel_destroy(send);
>  }
>  
> +static bool multifd_send_cleanup_channel(MultiFDSendParams *p, Error **errp)
> +{
> +    if (p->registered_yank) {
> +        migration_ioc_unregister_yank(p->c);
> +    }
> +    multifd_send_channel_destroy(p->c);
> +    p->c = NULL;
> +    qemu_mutex_destroy(&p->mutex);
> +    qemu_sem_destroy(&p->sem);
> +    qemu_sem_destroy(&p->sem_sync);
> +    g_free(p->name);
> +    p->name = NULL;
> +    multifd_pages_clear(p->pages);
> +    p->pages = NULL;
> +    p->packet_len = 0;
> +    g_free(p->packet);
> +    p->packet = NULL;
> +    g_free(p->iov);
> +    p->iov = NULL;
> +    multifd_send_state->ops->send_cleanup(p, errp);
> +
> +    return *errp == NULL;

I think technically this would require the ERRP_GUARD() macro?

> +}
> +
> +static void multifd_send_cleanup_state(void)
> +{
> +    qemu_sem_destroy(&multifd_send_state->channels_ready);
> +    g_free(multifd_send_state->params);
> +    multifd_send_state->params = NULL;
> +    multifd_pages_clear(multifd_send_state->pages);
> +    multifd_send_state->pages = NULL;
> +    g_free(multifd_send_state);
> +    multifd_send_state = NULL;
> +}
> +
>  void multifd_save_cleanup(void)
>  {
>      int i;
> @@ -615,48 +670,20 @@ void multifd_save_cleanup(void)
>      if (!migrate_multifd()) {
>          return;
>      }
> +
>      multifd_send_terminate_threads();
> -    for (i = 0; i < migrate_multifd_channels(); i++) {
> -        MultiFDSendParams *p = &multifd_send_state->params[i];
>  
> -        if (p->running) {
> -            qemu_thread_join(&p->thread);
> -        }
> -    }
>      for (i = 0; i < migrate_multifd_channels(); i++) {
>          MultiFDSendParams *p = &multifd_send_state->params[i];
>          Error *local_err = NULL;
>  
> -        if (p->registered_yank) {
> -            migration_ioc_unregister_yank(p->c);
> -        }
> -        multifd_send_channel_destroy(p->c);
> -        p->c = NULL;
> -        qemu_mutex_destroy(&p->mutex);
> -        qemu_sem_destroy(&p->sem);
> -        qemu_sem_destroy(&p->sem_sync);
> -        g_free(p->name);
> -        p->name = NULL;
> -        multifd_pages_clear(p->pages);
> -        p->pages = NULL;
> -        p->packet_len = 0;
> -        g_free(p->packet);
> -        p->packet = NULL;
> -        g_free(p->iov);
> -        p->iov = NULL;
> -        multifd_send_state->ops->send_cleanup(p, &local_err);
> -        if (local_err) {
> +        if (!multifd_send_cleanup_channel(p, &local_err)) {
>              migrate_set_error(migrate_get_current(), local_err);
>              error_free(local_err);
>          }
>      }
> -    qemu_sem_destroy(&multifd_send_state->channels_ready);
> -    g_free(multifd_send_state->params);
> -    multifd_send_state->params = NULL;
> -    multifd_pages_clear(multifd_send_state->pages);
> -    multifd_send_state->pages = NULL;
> -    g_free(multifd_send_state);
> -    multifd_send_state = NULL;
> +
> +    multifd_send_cleanup_state();
>  }
>  
>  static int multifd_zero_copy_flush(QIOChannel *c)