Re: [Qemu-devel] [PATCH v3 5/6] migration: implement bi-directional RDMA QIOChannel

[Paolo Bonzini]

On 05/05/2018 16:35, Lidong Chen wrote:
> @@ -2635,12 +2637,20 @@ static ssize_t qio_channel_rdma_writev(QIOChannel 
> *ioc,
>  {
>      QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(ioc);
>      QEMUFile *f = rioc->file;
> -    RDMAContext *rdma = rioc->rdma;
> +    RDMAContext *rdma;
>      int ret;
>      ssize_t done = 0;
>      size_t i;
>      size_t len = 0;
>  
> +    rcu_read_lock();
> +    rdma = atomic_rcu_read(&rioc->rdmaout);
> +
> +    if (!rdma) {
> +        rcu_read_unlock();
> +        return -EIO;
> +    }
> +
>      CHECK_ERROR_STATE();
>  
>      /*

I am not sure I understand this.  It would probably be wrong to use the
output side from two threads at the same time, so why not use two mutexes?

Also, who is calling qio_channel_rdma_close in such a way that another
thread is still using it?  Would it be possible to synchronize with the
other thread *before*, for example with qemu_thread_join?

Thanks,

Paolo