> -----Original Message----- > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Chas Williams > Sent: Wednesday, September 6, 2017 11:46 AM > To: Nicolau, Radu <radu.nico...@intel.com>; dev@dpdk.org > Cc: olivier.m...@6wind.com; cw8...@att.com > Subject: Re: [dpdk-dev] [PATCH v2] mbuf: use refcnt = 0 when debugging > > [Note: My former email address is going away eventually. I am moving the > conversation to my other email address which is a bit more permanent.] > > On Mon, 2017-09-04 at 15:27 +0100, Radu Nicolau wrote: > > > > On 8/7/2017 5:11 PM, Charles (Chas) Williams wrote: > > > After commit 8f094a9ac5d7 ("mbuf: set mbuf fields while in pool") is it > > > much harder to detect a "double free". If the developer makes a copy > > > of an mbuf pointer and frees it twice, this condition is never detected > > > and the mbuf gets returned to the pool twice. > > > > > > Since this requires extra work to track, make this behavior conditional > > > on CONFIG_RTE_LIBRTE_MBUF_DEBUG. > > > > > > Signed-off-by: Chas Williams <ciwil...@brocade.com> > > > --- > > > > > > @@ -1304,10 +1329,13 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m) > > > m->next = NULL; > > > m->nb_segs = 1; > > > } > > > +#ifdef RTE_LIBRTE_MBUF_DEBUG > > > + rte_mbuf_refcnt_set(m, RTE_MBUF_UNUSED_CNT); > > > +#endif > > > > > > return m; > > > > > > - } else if (rte_atomic16_add_return(&m->refcnt_atomic, -1) == 0) { > > > + } else if (rte_mbuf_refcnt_update(m, -1) == 0) { > > Why replace the use of atomic operation? > > It doesn't. rte_mbuf_refcnt_update() is also atomic(ish) but it slightly more > optimal. This whole section is a little hazy actually. It looks like > rte_pktmbuf_prefree_seg() unwraps rte_mbuf_refcnt_update() so they can avoid > setting the refcnt when the refcnt is already the 'correct' value.
You don't need to use refcnt_update() here - if you take that path it already means that m->refcnt_atomic != 1. In fact, I think using refcnt_update () here might be a bit slower - as it means extra read. Konstantin > > > > > > > > > > if (RTE_MBUF_INDIRECT(m)) > > > @@ -1317,7 +1345,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m) > > > m->next = NULL; > > > m->nb_segs = 1; > > > } > > > - rte_mbuf_refcnt_set(m, 1); > > > + rte_mbuf_refcnt_set(m, RTE_MBUF_UNUSED_CNT); > > > > > > return m; > > > } > > Reviewed-by: Radu Nicolau <radu.nico...@intel.com> > > Thanks for the review.
