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

[yang_y_yi <yang_y_yi@163.com>]

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.





















At 2020-10-14 09:00:12, "Hu, Jiayu" <jiayu.hu@intel.com> wrote:
>
>
>> -----Original Message-----
>> From: Ananyev, Konstantin <konstantin.ananyev@intel.com>
>> Sent: Tuesday, October 13, 2020 11:39 PM
>> To: Hu, Jiayu <jiayu.hu@intel.com>; yang_y_yi@163.com; dev@dpdk.org
>> Cc: mark.b.kavanagh@intel.com; olivier.matz@6wind.com;
>> thomas@monjalon.net; yangyi01@inspur.com
>> Subject: RE: [PATCH] gso: fix free issue of mbuf gso segments attach to
>> 
>> 
>> > > rte_gso_segment decreased refcnt of pkt by one, but
>> > > it is wrong if pkt is external mbuf, pkt won't be
>> > > freed because of incorrect refcnt, the result is
>> > > application can't allocate mbuf from mempool because
>> > > mbufs in mempool are run out of.
>> > >
>> > > One correct way is application should call
>> > > rte_pktmbuf_free after calling rte_gso_segment to free
>> > > pkt explicitly. rte_gso_segment mustn't handle it, this
>> > > should be responsibility of application.
>> >
>> > GSO doesn't support the input pktmbuf has external buffer.
>> > Indeed, requiring users to free the input pktmbuf can avoid
>> > memory leak, but I'm afraid that it also changes the semantic
>> > of rte_gso_segment() which is defined in rte_gso.h.
>> >
>> > @Konstantin, any suggestions?
>> 
>> Probably, a stupid question, but why can't we call mbuf_free()
>> here instead fo decrementing refcnt manually:
>> if (ret > 1)
>> rte_pktmbuf_free(pkt);
>> else if ...
>> ?
>
>You are right. Freeing mbuf inside GSO is a better way to solve
>the problem.
>
>Thanks,
>Jiayu
>> 
>> 
>> 
>> >
>> > Thanks,
>> > Jiayu
>> > >
>> > > Fixes: 119583797b6a ("gso: support TCP/IPv4 GSO")
>> > > Signed-off-by: Yi Yang <yangyi01@inspur.com>
>> > > ---
>> > >  doc/guides/prog_guide/generic_segmentation_offload_lib.rst | 7 +++++-
>> -
>> > >  lib/librte_gso/rte_gso.c                                   | 9 +--------
>> > >  2 files changed, 6 insertions(+), 10 deletions(-)
>> > >
>> > > diff --git a/doc/guides/prog_guide/generic_segmentation_offload_lib.rst
>> > > b/doc/guides/prog_guide/generic_segmentation_offload_lib.rst
>> > > index 205cb8a..8577572 100644
>> > > --- a/doc/guides/prog_guide/generic_segmentation_offload_lib.rst
>> > > +++ b/doc/guides/prog_guide/generic_segmentation_offload_lib.rst
>> > > @@ -25,8 +25,9 @@ Bearing that in mind, the GSO library enables DPDK
>> > > applications to segment
>> > >  packets in software. Note however, that GSO is implemented as a
>> > > standalone
>> > >  library, and not via a 'fallback' mechanism (i.e. for when TSO is
>> unsupported
>> > >  in the underlying hardware); that is, applications must explicitly invoke
>> the
>> > > -GSO library to segment packets. The size of GSO segments ``(segsz)`` is
>> > > -configurable by the application.
>> > > +GSO library to segment packets, they also must call
>> ``rte_pktmbuf_free()`` to
>> > > +free mbuf GSO segments attach to after calling ``rte_gso_segment()``.
>> The
>> > > size
>> > > +of GSO segments ``(segsz)`` is configurable by the application.
>> > >
>> > >  Limitations
>> > >  -----------
>> > > @@ -233,6 +234,8 @@ To segment an outgoing packet, an application
>> must:
>> > >
>> > >  #. Invoke the GSO segmentation API, ``rte_gso_segment()``.
>> > >
>> > > +#. Call ``rte_pktmbuf_free()`` to free mbuf ``rte_gso_segment()``
>> segments.
>> > > +
>> > >  #. If required, update the L3 and L4 checksums of the newly-created
>> > > segments.
>> > >     For tunneled packets, the outer IPv4 headers' checksums should also
>> be
>> > >     updated. Alternatively, the application may offload checksum
>> calculation
>> > > diff --git a/lib/librte_gso/rte_gso.c b/lib/librte_gso/rte_gso.c
>> > > index 751b5b6..0d6cae5 100644
>> > > --- a/lib/librte_gso/rte_gso.c
>> > > +++ b/lib/librte_gso/rte_gso.c
>> > > @@ -30,7 +30,6 @@
>> > >  uint16_t nb_pkts_out)
>> > >  {
>> > >  struct rte_mempool *direct_pool, *indirect_pool;
>> > > -struct rte_mbuf *pkt_seg;
>> > >  uint64_t ol_flags;
>> > >  uint16_t gso_size;
>> > >  uint8_t ipid_delta;
>> > > @@ -80,13 +79,7 @@
>> > >  return 1;
>> > >  }
>> > >
>> > > -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 < 0) {
>> > >  /* Revert the ol_flags in the event of failure. */
>> > >  pkt->ol_flags = ol_flags;
>> > >  }
>> > > --
>> > > 1.8.3.1
>> >
>>