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When dispatch/combine, neither sender nor receiver waits
for the finish of the rdma channel head update, which may
result in the remaining inflight head update wqes even after
the kernel finished. Once the infight wqes arrive after the
rdma channel head buffer cleaning for the next round of
dispatch/combine, the rdma channel head buffer will be re-
written to a none-zero value. The rdma sender can reuse the
data buffer before the rdma receivers consume the date buffer
because of the wrong rdma channel head, cauing date error and
kernel hung.
For performance considering, to overlap the inflight wqes' RTT,
fix this issue by waiting for all previous inflight wqes to
complete before cleaning rdma buffers in the next round of
dispatch/combine.
Signed-off-by: Guangguan Wang <guangguan.wang@linux.alibaba.com>