Re: [dpdk-stable] [dpdk-dev] [PATCH] af_xdp: avoid deadlock due to empty fill queue

Re: [dpdk-stable] [dpdk-dev] [PATCH] af_xdp: avoid deadlock due to empty fill queue

[Loftus, Ciara]

> when receive packets, it is possible to fail to reserve
> fill queue, since buffer ring is shared between tx and rx,
> and maybe not available temporary. at last, both fill
> queue and rx queue are empty.
> 
> then kernel side will be unable to receive packets due to
> empty fill queue, and dpdk will be unable to reserve fill
> queue because dpdk has not pakcets to receive, at last
> deadlock will happen
> 
> so move reserve fill queue before xsk_ring_cons__peek
> to fix it
> 
> Signed-off-by: Li RongQing <lirongqing@baidu.com>

Thanks for the fix. I tested and saw no significant performance drop.

Minor: the first line of the commit should read "net/af_xdp: ...."

Acked-by: Ciara Loftus <ciara.loftus@intel.com>

CC-ing stable as I think this fix should be considered for inclusion.

Thanks,
Ciara

> ---
>  drivers/net/af_xdp/rte_eth_af_xdp.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c
> b/drivers/net/af_xdp/rte_eth_af_xdp.c
> index 7ce4ad04a..2dc9cab27 100644
> --- a/drivers/net/af_xdp/rte_eth_af_xdp.c
> +++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
> @@ -304,6 +304,10 @@ af_xdp_rx_cp(void *queue, struct rte_mbuf **bufs,
> uint16_t nb_pkts)
>  	uint32_t free_thresh = fq->size >> 1;
>  	struct rte_mbuf *mbufs[ETH_AF_XDP_RX_BATCH_SIZE];
> 
> +	if (xsk_prod_nb_free(fq, free_thresh) >= free_thresh)
> +		(void)reserve_fill_queue(umem,
> ETH_AF_XDP_RX_BATCH_SIZE, NULL);
> +
> +
>  	if (unlikely(rte_pktmbuf_alloc_bulk(rxq->mb_pool, mbufs, nb_pkts)
> != 0))
>  		return 0;
> 
> @@ -317,9 +321,6 @@ af_xdp_rx_cp(void *queue, struct rte_mbuf **bufs,
> uint16_t nb_pkts)
>  		goto out;
>  	}
> 
> -	if (xsk_prod_nb_free(fq, free_thresh) >= free_thresh)
> -		(void)reserve_fill_queue(umem,
> ETH_AF_XDP_RX_BATCH_SIZE, NULL);
> -
>  	for (i = 0; i < rcvd; i++) {
>  		const struct xdp_desc *desc;
>  		uint64_t addr;
> --
> 2.16.2

Re: [dpdk-stable] [dpdk-dev] [PATCH] af_xdp: avoid deadlock due to empty fill queue

[Li,Rongqing]

> -----Original Message-----
> From: Loftus, Ciara [mailto:ciara.loftus@intel.com]
> Sent: Friday, September 18, 2020 5:27 PM
> To: Li,Rongqing <lirongqing@baidu.com>; dev@dpdk.org
> Cc: stable@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH] af_xdp: avoid deadlock due to empty fill queue
> 
> > when receive packets, it is possible to fail to reserve fill queue,
> > since buffer ring is shared between tx and rx, and maybe not available
> > temporary. at last, both fill queue and rx queue are empty.
> >
> > then kernel side will be unable to receive packets due to empty fill
> > queue, and dpdk will be unable to reserve fill queue because dpdk has
> > not pakcets to receive, at last deadlock will happen
> >
> > so move reserve fill queue before xsk_ring_cons__peek to fix it
> >
> > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> 
> Thanks for the fix. I tested and saw no significant performance drop.
> 
> Minor: the first line of the commit should read "net/af_xdp: ...."
> 
> Acked-by: Ciara Loftus <ciara.loftus@intel.com>
> 
> CC-ing stable as I think this fix should be considered for inclusion.
> 
> Thanks,
> Ciara
> 

Thanks, I will send v2

-Li


> > ---
> >  drivers/net/af_xdp/rte_eth_af_xdp.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/af_xdp/rte_eth_af_xdp.c
> > b/drivers/net/af_xdp/rte_eth_af_xdp.c
> > index 7ce4ad04a..2dc9cab27 100644
> > --- a/drivers/net/af_xdp/rte_eth_af_xdp.c
> > +++ b/drivers/net/af_xdp/rte_eth_af_xdp.c
> > @@ -304,6 +304,10 @@ af_xdp_rx_cp(void *queue, struct rte_mbuf **bufs,
> > uint16_t nb_pkts)
> >  	uint32_t free_thresh = fq->size >> 1;
> >  	struct rte_mbuf *mbufs[ETH_AF_XDP_RX_BATCH_SIZE];
> >
> > +	if (xsk_prod_nb_free(fq, free_thresh) >= free_thresh)
> > +		(void)reserve_fill_queue(umem,
> > ETH_AF_XDP_RX_BATCH_SIZE, NULL);
> > +
> > +
> >  	if (unlikely(rte_pktmbuf_alloc_bulk(rxq->mb_pool, mbufs, nb_pkts) !=
> > 0))
> >  		return 0;
> >
> > @@ -317,9 +321,6 @@ af_xdp_rx_cp(void *queue, struct rte_mbuf **bufs,
> > uint16_t nb_pkts)
> >  		goto out;
> >  	}
> >
> > -	if (xsk_prod_nb_free(fq, free_thresh) >= free_thresh)
> > -		(void)reserve_fill_queue(umem,
> > ETH_AF_XDP_RX_BATCH_SIZE, NULL);
> > -
> >  	for (i = 0; i < rcvd; i++) {
> >  		const struct xdp_desc *desc;
> >  		uint64_t addr;
> > --
> > 2.16.2