RE: [PATCH] net/mana: fix wrong indexing on CQE error when coalescing is used

[Long Li <longli@microsoft.com>]

> Subject: Re: [PATCH] net/mana: fix wrong indexing on CQE error when coalescing
> is used
> 
> On 7/7/2023 1:17 AM, longli@linuxonhyperv.com wrote:
> > From: Long Li <longli@microsoft.com>
> >
> > On a fatal CQE error when coalescing is used, update the correct index
> > and allow proceeding to the next CQE.
> >
> > Fixes: 3409e0f172f6 ("net/mana: implement Rx CQE coalescing")
> >
> 
> Is above fixes commit correct?
> Logic for 'CQE_RX_COALESCED_4' is not changed with this commit, in above
> commit and in this commit both does breaks the loop.

Yes, the "Fixes" tag is correct. Here CQE_RX_COALESCED_4 is rearranged to make it easier to read, but it doesn't change the behavior.

> 
> This commit changes logic for 'CQE_RX_TRUNCATED' and 'default' cases, which
> are added with different commits, not the one in fixes line.
> 
> "fatal CQE error when coalescing" mentioned in the commit log, to which switch
> case does this corresponds to?

The previous patch (3409e0f172f6 ) introduced variable "i", an index to completion CQEs. But both 'default' and 'CQE_RX_TRUNCATED' cases don't advance "i", hence not advance to next CQE on error.

The fatal CQE error means the "default" case. On 'CQE_RX_TRUNCATED' the code can recover when all CQEs are read. But on "default", it's a dead loop.

> 
> 
> > Signed-off-by: Long Li <longli@microsoft.com>
> > ---
> >  drivers/net/mana/rx.c | 18 ++++++++----------
> >  1 file changed, 8 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/net/mana/rx.c b/drivers/net/mana/rx.c index
> > cacfd9ae1b..220b372b15 100644
> > --- a/drivers/net/mana/rx.c
> > +++ b/drivers/net/mana/rx.c
> > @@ -416,23 +416,21 @@ mana_rx_burst(void *dpdk_rxq, struct rte_mbuf
> > **pkts, uint16_t pkts_n)
> >
> >  		switch (oob->cqe_hdr.cqe_type) {
> >  		case CQE_RX_OKAY:
> > +		case CQE_RX_COALESCED_4:
> >  			/* Proceed to process mbuf */
> >  			break;
> >
> >  		case CQE_RX_TRUNCATED:
> > -			DP_LOG(DEBUG, "Drop a truncated packet");
> > +		default:
> > +			DP_LOG(ERR, "RX CQE type %d client %d vendor %d",
> > +			       oob->cqe_hdr.cqe_type, oob->cqe_hdr.client_type,
> > +			       oob->cqe_hdr.vendor_err);
> > +
> >  			rxq->stats.errors++;
> >  			rte_pktmbuf_free(mbuf);
> > -			goto drop;
> > -
> > -		case CQE_RX_COALESCED_4:
> > -			/* Proceed to process mbuf */
> > -			break;
> >
> > -		default:
> > -			DP_LOG(ERR, "Unknown RX CQE type %d",
> > -			       oob->cqe_hdr.cqe_type);
> > -			continue;
> > +			i++;
> > +			goto drop;
> >  		}
> >
> >  		DP_LOG(DEBUG, "mana_rx_comp_oob type %d rxq %p",