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Date: Wed, 27 Mar 2019 08:18:38 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Chas Williams <3chas3@gmail.com>
Cc: dev@dpdk.org, Stephen Hemminger <sthemmin@microsoft.com>
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Subject: Re: [dpdk-dev] [PATCH] net: fix rte_vlan_insert with shared mbuf
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On Tue, 26 Mar 2019 18:38:57 -0400
Chas Williams <3chas3@gmail.com> wrote:
> On 3/26/19 3:15 PM, Stephen Hemminger wrote:
> > If mbuf refcnt was > 1 then rte_vlan_insert() would incorrectly
> > modify the original copy. Original code was expecting clone to make
> > a copy (it doesn't). Better to let the caller deal with making
> > a copy or setting up mbuf chain to allow for header to be added.
> >
> > Also fix docbook comment about parameters (function takes
> > pointer to mbuf).
> >
> > Fixes: c974021a5949 ("ether: add soft vlan encap/decap")
> > Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
> > ---
> > lib/librte_net/rte_ether.h | 15 ++++-----------
> > 1 file changed, 4 insertions(+), 11 deletions(-)
> >
> > diff --git a/lib/librte_net/rte_ether.h b/lib/librte_net/rte_ether.h
> > index c2c5e249ffe9..bab2b198fa79 100644
> > --- a/lib/librte_net/rte_ether.h
> > +++ b/lib/librte_net/rte_ether.h
> > @@ -374,7 +374,7 @@ static inline int rte_vlan_strip(struct rte_mbuf *m)
> > * Software version of VLAN unstripping
> > *
> > * @param m
> > - * The packet mbuf.
> > + * Pointer to the packet mbuf.
> > * @return
> > * - 0: On success
> > * -EPERM: mbuf is is shared overwriting would be unsafe
> > @@ -385,16 +385,9 @@ static inline int rte_vlan_insert(struct rte_mbuf **m)
> > struct ether_hdr *oh, *nh;
> > struct vlan_hdr *vh;
> >
> > - /* Can't insert header if mbuf is shared */
> > - if (rte_mbuf_refcnt_read(*m) > 1) {
> > - struct rte_mbuf *copy;
> > -
> > - copy = rte_pktmbuf_clone(*m, (*m)->pool);
> > - if (unlikely(copy == NULL))
> > - return -ENOMEM;
> > - rte_pktmbuf_free(*m);
> > - *m = copy;
> > - }
> > + /* Can't directly insert header if mbuf is shared */
> > + if (rte_mbuf_refcnt_read(*m) > 1)
>
> This check probably isn't sufficient. You need something more like:
>
> if (rte_mbuf_refcnt_read(mbuf) > 1 ||
> (RTE_MBUF_INDIRECT(mbuf) &&
> rte_mbuf_refcnt_read(rte_mbuf_from_indirect(mbuf)) > 1)) {
>
> If this is a cloned packet, the refcnt will be 1. So you need to examine
> the parent mbuf to see if other clones exist.
>
The problem is that indirect buffers probably can't be overwritten
because of lack of headroom.
Actually, why not push the problem into the pktmbuf_headroom logic?
From mboxrd@z Thu Jan 1 00:00:00 1970
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Date: Wed, 27 Mar 2019 08:18:38 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Chas Williams <3chas3@gmail.com>
Cc: dev@dpdk.org, Stephen Hemminger <sthemmin@microsoft.com>
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Subject: Re: [dpdk-dev] [PATCH] net: fix rte_vlan_insert with shared mbuf
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On Tue, 26 Mar 2019 18:38:57 -0400
Chas Williams <3chas3@gmail.com> wrote:
> On 3/26/19 3:15 PM, Stephen Hemminger wrote:
> > If mbuf refcnt was > 1 then rte_vlan_insert() would incorrectly
> > modify the original copy. Original code was expecting clone to make
> > a copy (it doesn't). Better to let the caller deal with making
> > a copy or setting up mbuf chain to allow for header to be added.
> >
> > Also fix docbook comment about parameters (function takes
> > pointer to mbuf).
> >
> > Fixes: c974021a5949 ("ether: add soft vlan encap/decap")
> > Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
> > ---
> > lib/librte_net/rte_ether.h | 15 ++++-----------
> > 1 file changed, 4 insertions(+), 11 deletions(-)
> >
> > diff --git a/lib/librte_net/rte_ether.h b/lib/librte_net/rte_ether.h
> > index c2c5e249ffe9..bab2b198fa79 100644
> > --- a/lib/librte_net/rte_ether.h
> > +++ b/lib/librte_net/rte_ether.h
> > @@ -374,7 +374,7 @@ static inline int rte_vlan_strip(struct rte_mbuf *m)
> > * Software version of VLAN unstripping
> > *
> > * @param m
> > - * The packet mbuf.
> > + * Pointer to the packet mbuf.
> > * @return
> > * - 0: On success
> > * -EPERM: mbuf is is shared overwriting would be unsafe
> > @@ -385,16 +385,9 @@ static inline int rte_vlan_insert(struct rte_mbuf **m)
> > struct ether_hdr *oh, *nh;
> > struct vlan_hdr *vh;
> >
> > - /* Can't insert header if mbuf is shared */
> > - if (rte_mbuf_refcnt_read(*m) > 1) {
> > - struct rte_mbuf *copy;
> > -
> > - copy = rte_pktmbuf_clone(*m, (*m)->pool);
> > - if (unlikely(copy == NULL))
> > - return -ENOMEM;
> > - rte_pktmbuf_free(*m);
> > - *m = copy;
> > - }
> > + /* Can't directly insert header if mbuf is shared */
> > + if (rte_mbuf_refcnt_read(*m) > 1)
>
> This check probably isn't sufficient. You need something more like:
>
> if (rte_mbuf_refcnt_read(mbuf) > 1 ||
> (RTE_MBUF_INDIRECT(mbuf) &&
> rte_mbuf_refcnt_read(rte_mbuf_from_indirect(mbuf)) > 1)) {
>
> If this is a cloned packet, the refcnt will be 1. So you need to examine
> the parent mbuf to see if other clones exist.
>
The problem is that indirect buffers probably can't be overwritten
because of lack of headroom.
Actually, why not push the problem into the pktmbuf_headroom logic?