Move the dma_rmb() between pending_scrq() and ibmvnic_next_scrq()
into the end of pending_scrq(), and explain why.
Explain in detail why the dma_rmb() is placed at the end of
ibmvnic_next_scrq().
Fixes: b71ec9522346 ("ibmvnic: Ensure that SCRQ entry reads are correctly
ordered")
Signed-off-by: Lijun Pan <l...@linux.ibm.com>
---
drivers/net/ethernet/ibm/ibmvnic.c | 41 +++++++++++++++++-------------
1 file changed, 24 insertions(+), 17 deletions(-)
diff --git a/drivers/net/ethernet/ibm/ibmvnic.c
b/drivers/net/ethernet/ibm/ibmvnic.c
index 9778c83150f1..8e043683610f 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -2511,12 +2511,6 @@ static int ibmvnic_poll(struct napi_struct *napi, int
budget)
if (!pending_scrq(adapter, rx_scrq))
break;
- /* The queue entry at the current index is peeked at above
- * to determine that there is a valid descriptor awaiting
- * processing. We want to be sure that the current slot
- * holds a valid descriptor before reading its contents.
- */
- dma_rmb();
next = ibmvnic_next_scrq(adapter, rx_scrq);
rx_buff =
(struct ibmvnic_rx_buff *)be64_to_cpu(next->
@@ -3256,13 +3250,6 @@ static int ibmvnic_complete_tx(struct ibmvnic_adapter
*adapter,
int total_bytes = 0;
int num_packets = 0;
- /* The queue entry at the current index is peeked at above
- * to determine that there is a valid descriptor awaiting
- * processing. We want to be sure that the current slot
- * holds a valid descriptor before reading its contents.
- */
- dma_rmb();
-
next = ibmvnic_next_scrq(adapter, scrq);
for (i = 0; i < next->tx_comp.num_comps; i++) {
if (next->tx_comp.rcs[i])
@@ -3636,11 +3623,25 @@ static int pending_scrq(struct ibmvnic_adapter *adapter,
struct ibmvnic_sub_crq_queue *scrq)
{
union sub_crq *entry = &scrq->msgs[scrq->cur];
+ int rc;
if (entry->generic.first & IBMVNIC_CRQ_CMD_RSP)
- return 1;
+ rc = 1;
else
- return 0;
+ rc = 0;
+
+ /* Ensure that the entire SCRQ descriptor scrq->msgs
+ * has been loaded before reading its contents.
+ * This barrier makes sure this function's entry, esp.
+ * entry->generic.first & IBMVNIC_CRQ_CMD_RSP
+ * 1. is loaded before ibmvnic_next_scrq()'s
+ * entry->generic.first & IBMVNIC_CRQ_CMD_RSP;
+ * 2. OR is loaded before ibmvnic_poll()'s
+ * disable_scrq_irq()'s scrq->hw_irq.
+ */
+ dma_rmb();
+
+ return rc;
}
static union sub_crq *ibmvnic_next_scrq(struct ibmvnic_adapter *adapter,
@@ -3659,8 +3660,14 @@ static union sub_crq *ibmvnic_next_scrq(struct
ibmvnic_adapter *adapter,
}
spin_unlock_irqrestore(&scrq->lock, flags);
- /* Ensure that the entire buffer descriptor has been
- * loaded before reading its contents
+ /* Ensure that the entire SCRQ descriptor scrq->msgs
+ * has been loaded before reading its contents.
+ * This barrier makes sure this function's entry, esp.
+ * entry->generic.first & IBMVNIC_CRQ_CMD_RSP
+ * 1. is loaded before ibmvnic_poll()'s
+ * be64_to_cpu(next->rx_comp.correlator);
+ * 2. OR is loaded before ibmvnic_complet_tx()'s
+ * be32_to_cpu(next->tx_comp.correlators[i]).
*/
dma_rmb();
--
2.23.0
