On Sat, Feb 13, 2016 at 2:36 AM, Chuck Lever <chuck.lever@xxxxxxxxxx> wrote:
> Commit fe97b47cd623 ("xprtrdma: Use workqueue to process RPC/RDMA
> replies") replaced the reply tasklet with a workqueue that allows
> RPC replies to be processed in parallel. Thus the credit values in
> RPC-over-RDMA replies can applied in a different order than in
> which the server sent them.
>
> To fix this, revert commit eba8ff660b2d ("xprtrdma: Move credit
> update to RPC reply handler"). Done by hand to accommodate code
> changes that have occurred since then.
>
> Fixes: fe97b47cd623 ("xprtrdma: Use workqueue to process . . .")
> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
> ---
> net/sunrpc/xprtrdma/rpc_rdma.c | 9 +--------
> net/sunrpc/xprtrdma/verbs.c | 27 ++++++++++++++++++++++++++-
> net/sunrpc/xprtrdma/xprt_rdma.h | 1 +
> 3 files changed, 28 insertions(+), 9 deletions(-)
>
> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
> index c341225..0c45288 100644
> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
> @@ -797,7 +797,6 @@ rpcrdma_reply_handler(struct rpcrdma_rep *rep)
> __be32 *iptr;
> int rdmalen, status, rmerr;
> unsigned long cwnd;
> - u32 credits;
>
> dprintk("RPC: %s: incoming rep %p\n", __func__, rep);
You may also want to remove the extra header len checks from here.
Header len validity is already checked
in rpcrdma_update_granted_credits() function call before scheduling wq.
>
> @@ -930,15 +929,9 @@ out:
> if (req->rl_nchunks)
> r_xprt->rx_ia.ri_ops->ro_unmap_sync(r_xprt, req);
>
> - credits = be32_to_cpu(headerp->rm_credit);
> - if (credits == 0)
> - credits = 1; /* don't deadlock */
> - else if (credits > r_xprt->rx_buf.rb_max_requests)
> - credits = r_xprt->rx_buf.rb_max_requests;
> -
> spin_lock_bh(&xprt->transport_lock);
> cwnd = xprt->cwnd;
> - xprt->cwnd = credits << RPC_CWNDSHIFT;
> + xprt->cwnd = atomic_read(&r_xprt->rx_buf.rb_credits) << RPC_CWNDSHIFT;
> if (xprt->cwnd > cwnd)
> xprt_release_rqst_cong(rqst->rq_task);
>
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index 878f1bf..fc1ef5f 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -190,6 +190,28 @@ rpcrdma_receive_worker(struct work_struct *work)
> rpcrdma_reply_handler(rep);
> }
>
> +/* Perform basic sanity checking to avoid using garbage
> + * to update the credit grant value.
> + */
> +static void
> +rpcrdma_update_granted_credits(struct rpcrdma_rep *rep)
> +{
> + struct rpcrdma_msg *rmsgp = rdmab_to_msg(rep->rr_rdmabuf);
> + struct rpcrdma_buffer *buffer = &rep->rr_rxprt->rx_buf;
> + u32 credits;
> +
> + if (rep->rr_len < RPCRDMA_HDRLEN_ERR)
> + return;
> +
> + credits = be32_to_cpu(rmsgp->rm_credit);
> + if (credits == 0)
> + credits = 1; /* don't deadlock */
> + else if (credits > buffer->rb_max_requests)
> + credits = buffer->rb_max_requests;
> +
> + atomic_set(&buffer->rb_credits, credits);
> +}
> +
> static void
> rpcrdma_recvcq_process_wc(struct ib_wc *wc)
> {
> @@ -211,7 +233,8 @@ rpcrdma_recvcq_process_wc(struct ib_wc *wc)
> ib_dma_sync_single_for_cpu(rep->rr_device,
> rdmab_addr(rep->rr_rdmabuf),
> rep->rr_len, DMA_FROM_DEVICE);
> - prefetch(rdmab_to_msg(rep->rr_rdmabuf));
do you really want to remove prefetch()?
> +
> + rpcrdma_update_granted_credits(rep);
>
> out_schedule:
> queue_work(rpcrdma_receive_wq, &rep->rr_work);
> @@ -330,6 +353,7 @@ rpcrdma_conn_upcall(struct rdma_cm_id *id, struct rdma_cm_event *event)
> connected:
> dprintk("RPC: %s: %sconnected\n",
> __func__, connstate > 0 ? "" : "dis");
> + atomic_set(&xprt->rx_buf.rb_credits, 1);
> ep->rep_connected = connstate;
> rpcrdma_conn_func(ep);
> wake_up_all(&ep->rep_connect_wait);
> @@ -943,6 +967,7 @@ rpcrdma_buffer_create(struct rpcrdma_xprt *r_xprt)
> buf->rb_max_requests = r_xprt->rx_data.max_requests;
> buf->rb_bc_srv_max_requests = 0;
> spin_lock_init(&buf->rb_lock);
> + atomic_set(&buf->rb_credits, 1);
Will this give a slow start to server initially? should it be rb_max_requests?
I am not sure, just raising a flag to bring your notice.
>
> rc = ia->ri_ops->ro_init(r_xprt);
> if (rc)
> diff --git a/net/sunrpc/xprtrdma/xprt_rdma.h b/net/sunrpc/xprtrdma/xprt_rdma.h
> index bf98c67..efd6fa7 100644
> --- a/net/sunrpc/xprtrdma/xprt_rdma.h
> +++ b/net/sunrpc/xprtrdma/xprt_rdma.h
> @@ -312,6 +312,7 @@ struct rpcrdma_buffer {
> struct list_head rb_send_bufs;
> struct list_head rb_recv_bufs;
> u32 rb_max_requests;
> + atomic_t rb_credits; /* most recent credit grant */
>
> u32 rb_bc_srv_max_requests;
> spinlock_t rb_reqslock; /* protect rb_allreqs */
>
> --
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