[dpdk-dev] [PATCH] net/enic: decrement Tx mbuf reference count before recycling

[John Daley (johndale)]

> -----Original Message-----
> From: Olivier Matz [mailto:olivier.matz at 6wind.com]
> Sent: Monday, July 11, 2016 3:04 AM
> To: John Daley (johndale) <johndale at cisco.com>; dev at dpdk.org
> Cc: bruce.richardson at intel.com
> Subject: Re: [dpdk-dev] [PATCH] net/enic: decrement Tx mbuf reference
> count before recycling
> 
> Hi John,
> 
> On 07/09/2016 12:22 AM, John Daley wrote:
> > In the Tx cleanup function, the reference count in mbufs to be
> > returned to the pool should to be decremented before they are
> > returned. Decrementing is not done by rte_mempool_put_bulk() so it
> > must be done separately using __rte_pktmbuf_prefree_seg().
> > If decrementing does not result in a 0 reference count the mbuf is not
> > returned to the pool and whatever has the last reference is
> > responsible for freeing.
> >
> > Fixes: 36935afbc53c ("net/enic: refactor Tx mbuf recycling")
> > Reviewed-by: Nelson Escobar <neescoba at cisco.com>
> > Signed-off-by: John Daley <johndale at cisco.com>
> > ---
> > Since reference counts are set to 0 when mbufs are reallocated from
> > the pool, and sending packets with reference count not equal to 1 is
> > probably an application error, this patch may not be critical. But a
> > debug ASSERT caught it and it would be nice to have it fixed in 16.07.
> 
> Sending a packet with refcnt != 1 is not an error. It can happen when using
> mbuf clones. So indeed it would be better to have in 16.07.
> 
> For the same reason, I also wonder if enic_free_wq_buf() should also be
> updated with:
> 
> -       rte_mempool_put(mbuf->pool, mbuf);
> +       rte_pktmbuf_free(mbuf);
That is a very good point, thank you. I'll use rte_pktmubf_free_seg(mbuf) though, since we are walking an array of all mbuf segments. V2 coming momentarily.
-john
> 
> 
> Regards,
> Olivier