Re: [dpdk-dev] [PATCH] gso: fix free issue of mbuf gso segments attach to

[yang_y_yi <yang_y_yi@163.com>]

At 2020-10-16 00:16:03, "Ananyev, Konstantin" <konstantin.ananyev@intel.com> wrote:
>
>
>> 
>> > -----Original Message-----
>> > From: Ananyev, Konstantin <konstantin.ananyev@intel.com>
>> > Sent: Wednesday, October 14, 2020 8:06 PM
>> > To: yang_y_yi <yang_y_yi@163.com>; Hu, Jiayu <jiayu.hu@intel.com>
>> > Cc: dev@dpdk.org; olivier.matz@6wind.com; thomas@monjalon.net;
>> > yangyi01@inspur.com
>> > Subject: RE: Re:RE: [PATCH] gso: fix free issue of mbuf gso segments attach to
>> >
>> >
>> > > From: yang_y_yi <yang_y_yi@163.com>
>> > > Sent: Wednesday, October 14, 2020 3:56 AM
>> > > To: Hu, Jiayu <jiayu.hu@intel.com>
>> > > Cc: Ananyev, Konstantin <konstantin.ananyev@intel.com>; dev@dpdk.org;
>> > olivier.matz@6wind.com; thomas@monjalon.net;
>> > > yangyi01@inspur.com
>> > > Subject: Re:RE: [PATCH] gso: fix free issue of mbuf gso segments attach to
>> > >
>> > > I think it isn't a good idea to free it in rte_gso_segment, maybe application
>> > will continue to use this pkt for other purpose, rte_gso_segment
>> > > can't make decision for application without any notice, it is better to return
>> > this decision right backt to application.
>> > >
>> >
>> > I think, if user wants to keep original packet, he can always call
>> > rte_pktmbuf_refcnt_update(pkt, 1)
>> > just before calling gso function.
>> >
>> > Also, as I remember in some cases it is not safe to do free() for input packet
>> > (as pkt_out[] can contain input pkt itself). Would it also be user responsibility
>> > to determine
>> > such situations?
>> 
>> In what case will pkt_out[] contain the input pkt? Can you give an example?
>
>As I can read the code, whenever gso code decides that
>no segmentation is not really needed, or it is not capable
>of doing it properly.
>Let say:
>
>gso_tcp4_segment(struct rte_mbuf *pkt,
>                uint16_t gso_size,
>                uint8_t ipid_delta,
>                struct rte_mempool *direct_pool,
>                struct rte_mempool *indirect_pool,
>                struct rte_mbuf **pkts_out,
>                uint16_t nb_pkts_out)
>{
>	...
>	/* Don't process the fragmented packet */
>        ipv4_hdr = (struct rte_ipv4_hdr *)(rte_pktmbuf_mtod(pkt, char *) +
>                        pkt->l2_len);
>        frag_off = rte_be_to_cpu_16(ipv4_hdr->fragment_offset);
>        if (unlikely(IS_FRAGMENTED(frag_off))) {
>                pkts_out[0] = pkt;
>                return 1;
>        }
>
>        /* Don't process the packet without data */
>        hdr_offset = pkt->l2_len + pkt->l3_len + pkt->l4_len;
>        if (unlikely(hdr_offset >= pkt->pkt_len)) {
>                pkts_out[0] = pkt;
>                return 1;
>        }
>
>That's why in rte_gso_segment() we update refcnt only when ret > 1. 
>	
>


This code block 

       if (ret > 1) {
               pkt_seg = pkt;
               while (pkt_seg) {
                       rte_mbuf_refcnt_update(pkt_seg, -1);
                       pkt_seg = pkt_seg->next;
               }
       }

should be equivalent to this

       if (ret > 1) {
               rte_pktmbuf_free(pkt);
       }

So not sure what the issue you're saying is.