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migration/multifd: fix hangup with TLS-Multifd due to blocking handshake

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The qemu main loop could hang up forever when we enable TLS+Multifd.
The Src multifd_send_0 invokes tls handshake, it sends hello to sever
and wait response.
However, the Dst main qemu loop has been waiting recvmsg() for multifd_recv_1.
Both of Src and Dst main qemu loop are blocking and waiting for reponse which
results in hanging up forever.

Src: (multifd_send_0)                                              Dst: (multifd_recv_1)
multifd_channel_connect                                            migration_channel_process_incoming
  multifd_tls_channel_connect                                        migration_tls_channel_process_incoming
    multifd_tls_channel_connect                                        qio_channel_tls_handshake_task
       qio_channel_tls_handshake                                         gnutls_handshake
          qio_channel_tls_handshake_task                                       ...
            qcrypto_tls_session_handshake                                      ...
              gnutls_handshake                                                 ...
                   ...                                                         ...
                recvmsg (Blocking I/O waiting for response)                recvmsg (Blocking I/O waiting for response)

Fix this by offloadinig handshake work to a background thread.

Reported-by: Yan Jin <jinyan12@huawei.com>
Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Chuan Zheng <zhengchuan@huawei.com>
Message-Id: <1604643893-8223-1-git-send-email-zhengchuan@huawei.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Chuan Zheng 2020-11-06 14:24:53 +08:00 committed by Dr. David Alan Gilbert
parent 136fc6aa2c
commit a1af605bd5
1 changed files with 17 additions and 6 deletions
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23
migration/multifd.c
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@ -739,6 +739,19 @@ static void multifd_tls_outgoing_handshake(QIOTask *task,
multifd_channel_connect(p, ioc, err);
}
static void *multifd_tls_handshake_thread(void *opaque)
{
MultiFDSendParams *p = opaque;
QIOChannelTLS *tioc = QIO_CHANNEL_TLS(p->c);
qio_channel_tls_handshake(tioc,
multifd_tls_outgoing_handshake,
p,
NULL,
NULL);
return NULL;
}
static void multifd_tls_channel_connect(MultiFDSendParams *p,
QIOChannel *ioc,
Error **errp)
@ -754,12 +767,10 @@ static void multifd_tls_channel_connect(MultiFDSendParams *p,
trace_multifd_tls_outgoing_handshake_start(ioc, tioc, hostname);
qio_channel_set_name(QIO_CHANNEL(tioc), "multifd-tls-outgoing");
qio_channel_tls_handshake(tioc,
multifd_tls_outgoing_handshake,
p,
NULL,
NULL);
p->c = QIO_CHANNEL(tioc);
qemu_thread_create(&p->thread, "multifd-tls-handshake-worker",
multifd_tls_handshake_thread, p,
QEMU_THREAD_JOINABLE);
}
static bool multifd_channel_connect(MultiFDSendParams *p,