[PATCH net v3] ibmvnic: Ensure that CRQ entry read are correctly ordered

[Lijun Pan <ljp@linux.ibm.com>]

Ensure that received Command-Response Queue (CRQ) entries are
properly read in order by the driver. dma_rmb barrier has
been added before accessing the CRQ descriptor to ensure
the entire descriptor is read before processing.

Fixes: 032c5e82847a ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: Lijun Pan <ljp@linux.ibm.com>
---
v3: reword the comments in the code to make it less confusing.
v2: drop dma_wmb according to Jakub's opinion

 drivers/net/ethernet/ibm/ibmvnic.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index 9778c83150f1..8820c98ea891 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -5084,6 +5084,12 @@ static void ibmvnic_tasklet(struct tasklet_struct *t)
 	while (!done) {
 		/* Pull all the valid messages off the CRQ */
 		while ((crq = ibmvnic_next_crq(adapter)) != NULL) {
+			/* This barrier makes sure ibmvnic_next_crq()'s
+			 * crq->generic.first & IBMVNIC_CRQ_CMD_RSP is loaded
+			 * before ibmvnic_handle_crq()'s
+			 * switch(gen_crq->first) and switch(gen_crq->cmd).
+			 */
+			dma_rmb();
 			ibmvnic_handle_crq(crq, adapter);
 			crq->generic.first = 0;
 		}
-- 
2.23.0