Re: [PATCH net v2] ibmvnic: Ensure that CRQ entry read are correctly ordered
From: Jakub Kicinski <kuba@kernel.org>
Date: 2021-01-28 01:04:23
On Mon, 25 Jan 2021 17:20:23 -0600 Lijun Pan wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- v2: drop dma_wmb according to Jakub's opinion drivers/net/ethernet/ibm/ibmvnic.c | 8 ++++++++ 1 file changed, 8 insertions(+)diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c index 9778c83150f1..d84369bd5fc9 100644 --- a/drivers/net/ethernet/ibm/ibmvnic.c +++ b/drivers/net/ethernet/ibm/ibmvnic.c@@ -5084,6 +5084,14 @@ 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) { + /* Ensure that the entire CRQ descriptor queue->msgs + * has been loaded before reading its contents.
I still find this sentence confusing, maybe you mean to say stored instead of loaded?
+ * 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).
Yup, that makes perfect sense. It's about ordering of the loads.
+ */ + dma_rmb(); ibmvnic_handle_crq(crq, adapter); crq->generic.first = 0; }