Re: [PATCH v2 2/3] migration: Make sure that we don't call write() in case of error

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

* Juan Quintela (quintela@redhat.com) wrote:
> If we are exiting due to an error/finish/.... Just don't try to even
> touch the channel with one IO operation.
> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  migration/ram.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 96feb4062c..6e678dbd2e 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -900,6 +900,12 @@ struct {
>      uint64_t packet_num;
>      /* send channels ready */
>      QemuSemaphore channels_ready;
> +    /*
> +     * Have we already run terminate threads.  There is a race when it
> +     * happens that we got one error while we are exiting.
> +     * We will use atomic operations.  Only valid values are 0 and 1.
> +     */
> +    int exiting;
>  } *multifd_send_state;
>  
>  /*
> @@ -928,6 +934,10 @@ static int multifd_send_pages(RAMState *rs)
>      MultiFDPages_t *pages = multifd_send_state->pages;
>      uint64_t transferred;
>  
> +    if (atomic_read(&multifd_send_state->exiting)) {
> +        return -1;
> +    }
> +
>      qemu_sem_wait(&multifd_send_state->channels_ready);
>      for (i = next_channel;; i = (i + 1) % migrate_multifd_channels()) {
>          p = &multifd_send_state->params[i];
> @@ -1009,6 +1019,16 @@ static void multifd_send_terminate_threads(Error *err)
>          }
>      }
>  
> +    /*
> +     * We don't want to exit each threads twice.  Depending on where
> +     * we get the error, or if there are two independent errors in two
> +     * threads at the same time, we can end calling this function
> +     * twice.
> +     */

Yeh that makes it cleaer.  Thanks

> +    if (atomic_xchg(&multifd_send_state->exiting, 1)) {
> +        return;
> +    }
> +
>      for (i = 0; i < migrate_multifd_channels(); i++) {
>          MultiFDSendParams *p = &multifd_send_state->params[i];
>  
> @@ -1118,6 +1138,10 @@ static void *multifd_send_thread(void *opaque)
>  
>      while (true) {
>          qemu_sem_wait(&p->sem);
> +
> +        if (atomic_read(&multifd_send_state->exiting)) {
> +            break;
> +        }
>          qemu_mutex_lock(&p->mutex);
>  
>          if (p->pending_job) {
> @@ -1224,6 +1248,7 @@ int multifd_save_setup(void)
>      multifd_send_state->params = g_new0(MultiFDSendParams, thread_count);
>      multifd_send_state->pages = multifd_pages_init(page_count);
>      qemu_sem_init(&multifd_send_state->channels_ready, 0);
> +    atomic_set(&multifd_send_state->exiting, 0);
>  
>      for (i = 0; i < thread_count; i++) {
>          MultiFDSendParams *p = &multifd_send_state->params[i];
> -- 
> 2.24.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK