From: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>
To: Chas Williams <3chas3@gmail.com>,
"Nicolau, Radu" <radu.nicolau@intel.com>,
"dev@dpdk.org" <dev@dpdk.org>
Cc: "olivier.matz@6wind.com" <olivier.matz@6wind.com>,
"cw817q@att.com" <cw817q@att.com>
Subject: Re: [dpdk-dev] [PATCH v2] mbuf: use refcnt = 0 when debugging
Date: Wed, 6 Sep 2017 14:53:52 +0000 [thread overview]
Message-ID: <2601191342CEEE43887BDE71AB9772584F2482B0@irsmsx105.ger.corp.intel.com> (raw)
In-Reply-To: <1504706130.2192.11.camel@gmail.com>
> -----Original Message-----
> From: Chas Williams [mailto:3chas3@gmail.com]
> Sent: Wednesday, September 6, 2017 2:56 PM
> To: Ananyev, Konstantin <konstantin.ananyev@intel.com>; Nicolau, Radu <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
>
> On Wed, 2017-09-06 at 11:58 +0000, Ananyev, Konstantin wrote:
> >
> > > -----Original Message-----
> > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Chas Williams
> > > Sent: Wednesday, September 6, 2017 11:46 AM
> > > To: Nicolau, Radu <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
> > >
> > > [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.
> >
> > 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
>
> Yes, that is somewhat the point. If a mbuf can have a refcnt of 0,
> then we want to go into rte_mbuf_refcnt_update() which detects 0 -> -1.
Woulnd't __rte_mbuf_sanity_check(m, 0) at the start of prefree_seg()
already catch it?
Konstantin
> I could explicitly check this in prefree_seg but I was just restored the
> previous call into refcnt_update. I could explicitly check for refcnt =
> 0 in prefree_seg() but since we do have a routine for this...
>
> > > > >
> > > > >
> > > > > 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 14:54 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
2017-09-06 11:58 ` Ananyev, Konstantin
2017-09-06 13:55 ` Chas Williams
2017-09-06 14:53 ` Ananyev, Konstantin [this message]
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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