On Tue, 16 Apr 2019 10:42:13 +0100 Bruce Richardson <bruce.richard...@intel.com> wrote:
> On Tue, Apr 16, 2019 at 10:37:07AM +0100, Ferruh Yigit wrote: > > On 4/12/2019 11:08 PM, Stephen Hemminger wrote: > > > On Fri, 12 Apr 2019 17:28:17 +0100 > > > Ferruh Yigit <ferruh.yi...@intel.com> wrote: > > > > > >> On 4/8/2019 5:41 PM, Stephen Hemminger wrote: > > >>> If the af_packet transmit is sending a VLAN packet, > > >>> and the transmit path to the kernel os full, then it would > > >>> mismanage the outgoing mbuf. The original mbuf would end up > > >>> being freed twice, once by AF_PACKET PMD and once by caller. > > >> > > >> This comment is valid with your new patch [1] that updates > > >> 'rte_vlan_insert()' > > >> to duplicate the mbuf, right? > > >> > > >> That patch looks like won't make the release, so I suggest this one wait > > >> that > > >> patch, although this is harmless on its own, commit log is misleading. > > >> > > >> [1] > > >> https://patches.dpdk.org/patch/51870/ > > > > > > It was always true, even with existing vlan_insert. > > > Existing vlan_insert has issues if it ever creates a clone packet. > > > Existing vlan_insert can duplicate mbuf through clone > > > > > > > Right, existing vlan_insert has same issue on af_packet. > > > > But, should vlan_insert try to duplicate the mbuf when it is shared, does it > > worth the complexity it brings? And when that support removed this patch > > won't > > be needed. > > I don't think vlan insert or other mbuf manipulation APIs should be > checking for shared state or not - that's the job of the app. We could have > cases where the user does want to modify a shared mbuf. > > Regards, > /Bruce The vlan_insert code is called on transmit, and there are lots of cases where a transmit mbuf might be shared (like TCP stack). And in that case inserting the vlan must be non-destructive to the original mbuf. Whether you want to push the problem to the driver or do it in the library, it is still a problem.
