On Wed, Jan 27, 2021 at 7:06 PM Jakub Kicinski <k...@kernel.org> wrote:
>
> On Mon, 25 Jan 2021 17:20:23 -0600 Lijun Pan wrote:
> > 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 <l...@linux.ibm.com>
> > ---
> > 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?
The above 2 lines are the general description. The below 4 lines are
detailed explanations. If it is still confusing, we can delete the above
2 lines of comments.
>
> > + * 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;
> > }
>
