[PATCH net-next V2 7/8] net: fec: don't transfer ownership until descriptor write is complete

On 2/6/2016 4:52 AM, Sergei Shtylyov wrote:

Hello.

On 2/6/2016 12:52 AM, Troy Kisky wrote:

quoted

If you don't own it, you shouldn't write to it.

Signed-off-by: Troy Kisky <redacted>
---
  drivers/net/ethernet/freescale/fec_main.c | 14 +++++++++++++-
  1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/freescale/fec_main.c b/drivers/net/ethernet/freescale/fec_main.c
index ca2708d..97ca72a 100644
--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c

@@ -390,6 +390,10 @@ fec_enet_txq_submit_frag_skb(struct fec_enet_priv_tx_q *txq,

          bdp->cbd_bufaddr = cpu_to_fec32(addr);
          bdp->cbd_datlen = cpu_to_fec16(frag_len);
+        /* Make sure the updates to rest of the descriptor are
+         * performed before transferring ownership.
+         */
+        wmb();
          bdp->cbd_sc = cpu_to_fec16(status);
      }

@@ -499,6 +503,10 @@ static int fec_enet_txq_submit_skb(struct fec_enet_priv_tx_q *txq,

      bdp->cbd_datlen = cpu_to_fec16(buflen);
      bdp->cbd_bufaddr = cpu_to_fec32(addr);
+    /* Make sure the updates to rest of the descriptor are performed before
+     * transferring ownership.
+     */
+    wmb();

      /* Send it on its way.  Tell FEC it's ready, interrupt when done,
       * it's the last BD of the frame, and to put the CRC on the end.

[...]

quoted

@@ -1484,6 +1491,11 @@ rx_processing_done:
              ebdp->cbd_prot = 0;
              ebdp->cbd_bdu = 0;
          }
+        /* Make sure the updates to rest of the descriptor are
+         * performed before transferring ownership.
+         */
+        wmb();
+        bdp->cbd_sc = cpu_to_fec16(status);

   I think you can use "ligter" dma_wmb() in this case.

Thanks for the review, I added a patch to the end of the series to address this.

Troy