nvme-rdma: support devices with queue size < 32

In the case of small NVMe-oF queue size (<32) we may enter a deadlock
caused by the fact that the IB completions aren't sent waiting for 32
and the send queue will fill up.

The error is seen as (using mlx5):
[ 2048.693355] mlx5_0:mlx5_ib_post_send:3765:(pid 7273):
[ 2048.693360] nvme nvme1: nvme_rdma_post_send failed with error code -12

This patch changes the way the signaling is done so that it depends on
the queue depth now. The magic define has been removed completely.

Cc: stable@vger.kernel.org
Signed-off-by: Marta Rybczynska <marta.rybczynska@kalray.eu>
Signed-off-by: Samuel Jones <sjones@kalray.eu>
Acked-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index dd1c6deef82fcf509b5c04af20d9df1c17746d9b..e2c18f3d9dcf551919cce825f5107c1773636a53 100644 (file)
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -1038,6 +1038,19 @@ static void nvme_rdma_send_done(struct ib_cq *cq, struct ib_wc *wc)
                nvme_rdma_wr_error(cq, wc, "SEND");
 }
 
+static inline int nvme_rdma_queue_sig_limit(struct nvme_rdma_queue *queue)
+{
+       int sig_limit;
+
+       /*
+        * We signal completion every queue depth/2 and also handle the
+        * degenerated case of a  device with queue_depth=1, where we
+        * would need to signal every message.
+        */
+       sig_limit = max(queue->queue_size / 2, 1);
+       return (++queue->sig_count % sig_limit) == 0;
+}
+
 static int nvme_rdma_post_send(struct nvme_rdma_queue *queue,
                struct nvme_rdma_qe *qe, struct ib_sge *sge, u32 num_sge,
                struct ib_send_wr *first, bool flush)
@@ -1065,9 +1078,6 @@ static int nvme_rdma_post_send(struct nvme_rdma_queue *queue,
         * Would have been way to obvious to handle this in hardware or
         * at least the RDMA stack..
         *
-        * This messy and racy code sniplet is copy and pasted from the iSER
-        * initiator, and the magic '32' comes from there as well.
-        *
         * Always signal the flushes. The magic request used for the flush
         * sequencer is not allocated in our driver's tagset and it's
         * triggered to be freed by blk_cleanup_queue(). So we need to
@@ -1075,7 +1085,7 @@ static int nvme_rdma_post_send(struct nvme_rdma_queue *queue,
         * embedded in request's payload, is not freed when __ib_process_cq()
         * calls wr_cqe->done().
         */
-       if ((++queue->sig_count % 32) == 0 || flush)
+       if (nvme_rdma_queue_sig_limit(queue) || flush)
                wr.send_flags |= IB_SEND_SIGNALED;
 
        if (first)