RE: [PATCH 15/15] net/dpaa: fix buffer free in slow path

[Gagandeep Singh <G.Singh@nxp.com>]

Hi,

> -----Original Message-----
> From: Ferruh Yigit <ferruh.yigit@amd.com>
> Sent: Wednesday, October 5, 2022 7:52 PM
> To: Gagandeep Singh <G.Singh@nxp.com>; dev@dpdk.org
> Cc: stable@dpdk.org
> Subject: Re: [PATCH 15/15] net/dpaa: fix buffer free in slow path
> 
> On 9/28/2022 6:25 AM, Gagandeep Singh wrote:
> > Adding a check in slow path to free those buffers which are not
> > external.
> >
> 
> Can you please explain what was the error before fix, what was happening
> when you try to free all mbufs?
> 
> Also it seems previous logic was different, with 'prev_seg' etc, can you
> explain what/why changed there?
> 
Actually, there were two issues, this function was converting all the segments present in HW frame
descriptor to mbuf SG list by doing while on segments in FD (HW descriptor) and in the end
it frees only one segment by calling the API rte_pktmbuf_free_seg(), so for other segments
memory will be leaked.

Now in this change, doing the loop on each segment in FD and if the segment has a valid
buffer pool id (HW pool id), freeing that segment in the loop itself without converting to a mbuf list.
if we free all the buffers even those with invalid HW bpid (which will only be the external buffer case),
then there can be double free because all the external buffer free handling is being done by the
Xmit function.

> > Fixes: 9124e65dd3eb ("net/dpaa: enable Tx queue taildrop")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Gagandeep Singh <g.singh@nxp.com>
> > ---
> >   drivers/net/dpaa/dpaa_rxtx.c | 23 ++++++++---------------
> >   1 file changed, 8 insertions(+), 15 deletions(-)
> >
> > diff --git a/drivers/net/dpaa/dpaa_rxtx.c
> > b/drivers/net/dpaa/dpaa_rxtx.c index 4d285b4f38..ce4f3d6c85 100644
> > --- a/drivers/net/dpaa/dpaa_rxtx.c
> > +++ b/drivers/net/dpaa/dpaa_rxtx.c
> > @@ -455,7 +455,7 @@ dpaa_free_mbuf(const struct qm_fd *fd)
> >   	bp_info = DPAA_BPID_TO_POOL_INFO(fd->bpid);
> >   	format = (fd->opaque & DPAA_FD_FORMAT_MASK) >>
> DPAA_FD_FORMAT_SHIFT;
> >   	if (unlikely(format == qm_fd_sg)) {
> > -		struct rte_mbuf *first_seg, *prev_seg, *cur_seg, *temp;
> > +		struct rte_mbuf *first_seg, *cur_seg;
> >   		struct qm_sg_entry *sgt, *sg_temp;
> >   		void *vaddr, *sg_vaddr;
> >   		int i = 0;
> > @@ -469,32 +469,25 @@ dpaa_free_mbuf(const struct qm_fd *fd)
> >   		sgt = vaddr + fd_offset;
> >   		sg_temp = &sgt[i++];
> >   		hw_sg_to_cpu(sg_temp);
> > -		temp = (struct rte_mbuf *)
> > -			((char *)vaddr - bp_info->meta_data_size);
> >   		sg_vaddr = DPAA_MEMPOOL_PTOV(bp_info,
> >
> 	qm_sg_entry_get64(sg_temp));
> > -
> >   		first_seg = (struct rte_mbuf *)((char *)sg_vaddr -
> >   						bp_info->meta_data_size);
> >   		first_seg->nb_segs = 1;
> > -		prev_seg = first_seg;
> >   		while (i < DPAA_SGT_MAX_ENTRIES) {
> >   			sg_temp = &sgt[i++];
> >   			hw_sg_to_cpu(sg_temp);
> > -			sg_vaddr = DPAA_MEMPOOL_PTOV(bp_info,
> > +			if (sg_temp->bpid != 0xFF) {
> > +				bp_info =
> DPAA_BPID_TO_POOL_INFO(sg_temp->bpid);
> > +				sg_vaddr = DPAA_MEMPOOL_PTOV(bp_info,
> >
> 	qm_sg_entry_get64(sg_temp));
> > -			cur_seg = (struct rte_mbuf *)((char *)sg_vaddr -
> > +				cur_seg = (struct rte_mbuf *)((char
> *)sg_vaddr -
> >   						      bp_info-
> >meta_data_size);
> > -			first_seg->nb_segs += 1;
> > -			prev_seg->next = cur_seg;
> > -			if (sg_temp->final) {
> > -				cur_seg->next = NULL;
> > -				break;
> > +				rte_pktmbuf_free_seg(cur_seg);
> >   			}
> > -			prev_seg = cur_seg;
> > +			if (sg_temp->final)
> > +				break;
> >   		}
> > -
> > -		rte_pktmbuf_free_seg(temp);
> >   		rte_pktmbuf_free_seg(first_seg);
> >   		return 0;
> >   	}