On Tue, May 15, 2018 at 10:54 PM, Paolo Bonzini <pbonz...@redhat.com> wrote:
> 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?
Two thread will not invoke qio_channel_rdma_writev at the same time.
The source qemu, migration thread only use writev, and the return path
thread only
use readv.
The destination qemu already have a mutex mis->rp_mutex to make sure
not use writev
at the same time.
The rcu_read_lock is used to protect not use RDMAContext when another
thread closes it.
>
> 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?
The MigrationState structure includes to_dst_file and from_dst_file
QEMUFile, the two QEMUFile use the same QIOChannel.
For example, if the return path thread call
qemu_fclose(ms->rp_state.from_dst_file),
It will also close the RDMAContext for ms->to_dst_file.
For live migration, the source qemu invokes qemu_fclose in different
threads include main thread, migration thread, return path thread.
The destination qemu invokes qemu_fclose in main thread, listen thread and
COLO incoming thread.
I do not find an effective way to synchronize these threads.
Thanks.
>
> Thanks,
>
> Paolo
