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

[Ananyev, Konstantin]

> > 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 ...
?



> 
> Thanks,
> Jiayu
> >
> > Fixes: 119583797b6a ("gso: support TCP/IPv4 GSO")
> > Signed-off-by: Yi Yang <yangyi01 at 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
>