From: Chas Williams <3chas3@gmail.com>
To: Radu Nicolau <radu.nicolau@intel.com>, dev@dpdk.org
Cc: olivier.matz@6wind.com, cw817q@att.com
Subject: Re: [dpdk-dev] [PATCH v2] mbuf: use refcnt = 0 when debugging
Date: Wed, 06 Sep 2017 06:46:13 -0400 [thread overview]
Message-ID: <1504694773.2192.9.camel@gmail.com> (raw)
In-Reply-To: <bff4a6bc-4a57-e9c4-4208-d5950f2f122b@intel.com>
[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 <ciwillia@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.
> >
> >
> > 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.nicolau@intel.com>
Thanks for the review.
next prev parent reply other threads:[~2017-09-06 10:46 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-07 15:37 [dpdk-dev] [PATCH] " Charles (Chas) Williams
2017-08-07 16:11 ` [dpdk-dev] [PATCH v2] " Charles (Chas) Williams
2017-09-04 14:27 ` Radu Nicolau
2017-09-06 10:46 ` Chas Williams [this message]
2017-09-06 11:58 ` Ananyev, Konstantin
2017-09-06 13:55 ` Chas Williams
2017-09-06 14:53 ` Ananyev, Konstantin
2017-09-07 15:55 ` Chas Williams
2017-09-07 21:21 ` [dpdk-dev] [PATCH v3] " Charles (Chas) Williams
2017-09-20 11:23 ` Olivier MATZ
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