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References: <1525530936-21835-1-git-send-email-lidongchen@tencent.com>
	<1525530936-21835-6-git-send-email-lidongchen@tencent.com>
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <379b3f13-f53f-966b-ccbf-66517d45aa9d@redhat.com>
Date: Tue, 15 May 2018 16:54:30 +0200
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Subject: Re: [Qemu-devel] [PATCH v3 5/6] migration: implement bi-directional
 RDMA QIOChannel
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To: Lidong Chen <jemmy858585@gmail.com>, quintela@redhat.com, dgilbert@redhat.com, berrange@redhat.com
Cc: adido@mellanox.com, galsha@mellanox.com, aviadye@mellanox.com, qemu-devel@nongnu.org, Lidong Chen <lidongchen@tencent.com>

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