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 08:53:00, "Hu, Jiayu" <jiayu.hu@intel.com> wrote:
>
>
>> -----Original Message-----
>> From: Ananyev, Konstantin <konstantin.ananyev@intel.com>
>> Sent: Friday, October 16, 2020 12:16 AM
>> To: Hu, Jiayu <jiayu.hu@intel.com>; yang_y_yi <yang_y_yi@163.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
>> 
>> 
>> 
>> >
>> > > -----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.
>
>But in these cases, the value of ret is 1. So we can free input pkt only when
>ret > 1. Like:
>
>-       if (ret > 1) {
>-               pkt_seg = pkt;
>-               while (pkt_seg) {
>-                       rte_mbuf_refcnt_update(pkt_seg, -1);
>-                       pkt_seg = pkt_seg->next;
>-               }
>-       } else if (ret < 0) {
>+       if (ret > 1)
>+               rte_pktmbuf_free(pkt);
>+       else if (ret < 0) {
>                /* Revert the ol_flags in the event of failure. */
>                pkt->ol_flags = ol_flags;
>        }
>
>Thanks,
>Jiayu
>> 
>> 
>> 

Jiayu, please help commit the patch you pasted if you think it is ok. I need to update my GSO patch based on this fix, thanks a lot.