Re: [dpdk-dev] [PATCH] ixgbe: fix crash caused by bulk allocation failure in vector pmd

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Balazs Nemeth
> Sent: Friday, September 26, 2014 10:57 AM
> To: dev@dpdk.org
> Cc: Nemeth, Balazs
> Subject: [dpdk-dev] [PATCH] ixgbe: fix crash caused by bulk allocation failure in vector pmd
> 
> Since the introduction of vector PMD, a bug in ixgbe_rxq_rearm could
> cause a crash. As long as the memory pool allocated to the RX queue
> has mbufs available, there is no problem. After allocation of _all_
> mbufs from the memory pool, previously returned mbufs by
> rte_eth_rx_burst could be accessed by subsequent calls to the PMD and
> could be returned by subsequent calls to rte_eth_rx_burst. From the
> perspective of the application, the means that fields within the mbuf
> could change and that previously allocated mbufs could appear multiple
> times.
> 
> After failure of mbuf allocation, the dd bits should indicate that the
> packets are not ready. For this, this patch adds code to reset the dd
> bits in the first RTE_IXGBE_DESCS_PER_LOOP packets of the next
> RTE_IXGBE_RXQ_REARM_THRESH packets only if the next
> RTE_IXGBE_RXQ_REARM_THRESH packets that will be accessed contain
> previously allocated packets.
> 
> Setting the bits is not enough. The bits are checked _after_ setting
> the mbuf fields, thus a mechanism is needed to prevent the previously
> used mbuf pointers from being accessed during the speculative load of
> the mbuf fields. For this reason, not only the dd bits are reset, but
> also the mbufs associated to those descriptors are set to point to a
> "fake" mbuf.
> 
> Signed-off-by: Balazs Nemeth <balazs.nemeth@intel.com>
> ---
>  lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> index 203ddf7..457f267 100644
> --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx_vec.c
> @@ -54,17 +54,28 @@ ixgbe_rxq_rearm(struct igb_rx_queue *rxq)
>  	struct rte_mbuf *mb0, *mb1;
>  	__m128i hdr_room = _mm_set_epi64x(RTE_PKTMBUF_HEADROOM,
>  			RTE_PKTMBUF_HEADROOM);
> +	__m128i dma_addr0, dma_addr1;
> +
> +	rxdp = rxq->rx_ring + rxq->rxrearm_start;
> 
>  	/* Pull 'n' more MBUFs into the software ring */
>  	if (rte_mempool_get_bulk(rxq->mb_pool,
> -				 (void *)rxep, RTE_IXGBE_RXQ_REARM_THRESH) < 0)
> +				 (void *)rxep,
> +				 RTE_IXGBE_RXQ_REARM_THRESH) < 0) {
> +		if (rxq->rxrearm_nb + RTE_IXGBE_RXQ_REARM_THRESH >=
> +		    rxq->nb_rx_desc) {
> +			dma_addr0 = _mm_xor_si128(dma_addr0, dma_addr0);
> +			for (i = 0; i < RTE_IXGBE_DESCS_PER_LOOP; i++) {
> +				rxep[i].mbuf = &rxq->fake_mbuf;
> +				_mm_store_si128((__m128i *)&rxdp[i].read,
> +						dma_addr0);
> +			}
> +		}
>  		return;
> -
> -	rxdp = rxq->rx_ring + rxq->rxrearm_start;
> +	}
> 
>  	/* Initialize the mbufs in vector, process 2 mbufs in one loop */
>  	for (i = 0; i < RTE_IXGBE_RXQ_REARM_THRESH; i += 2, rxep += 2) {
> -		__m128i dma_addr0, dma_addr1;
>  		__m128i vaddr0, vaddr1;
> 
>  		mb0 = rxep[0].mbuf;
> --
> 2.1.0

Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>