Re: [dpdk-dev] [PATCH] ethdev: fix wrong memset

[Thomas Monjalon <thomas.monjalon@6wind.com>]

2017-01-23 13:06, Ananyev, Konstantin:
> 
> > -----Original Message-----
> > From: Yuanhan Liu [mailto:yuanhan.liu@linux.intel.com]
> > Sent: Monday, January 23, 2017 12:53 PM
> > To: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> > Cc: Yigit, Ferruh <ferruh.yigit@intel.com>; dev@dpdk.org; Thomas Monjalon <thomas.monjalon@6wind.com>; Horton, Remy
> > <remy.horton@intel.com>
> > Subject: Re: [dpdk-dev] [PATCH] ethdev: fix wrong memset
> > 
> > On Mon, Jan 23, 2017 at 12:44:11PM +0000, Ananyev, Konstantin wrote:
> > > > On Mon, Jan 23, 2017 at 07:40:50PM +0800, Yuanhan Liu wrote:
> > > > > On Mon, Jan 23, 2017 at 11:32:23AM +0000, Ferruh Yigit wrote:
> > > > > > On 1/23/2017 11:24 AM, Yuanhan Liu wrote:
> > > > > > > On Mon, Jan 23, 2017 at 11:05:25AM +0000, Ferruh Yigit wrote:
> > > > > > >>>>>>>>  lib/librte_ether/rte_ethdev.c | 2 +-
> > > > > > >>>>>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > > >>>>>>>>
> > > > > > >>>>>>>> diff --git a/lib/librte_ether/rte_ethdev.c b/lib/librte_ether/rte_ethdev.c
> > > > > > >>>>>>>> index 4790faf..61f44e2 100644
> > > > > > >>>>>>>> --- a/lib/librte_ether/rte_ethdev.c
> > > > > > >>>>>>>> +++ b/lib/librte_ether/rte_ethdev.c
> > > > > > >>>>>>>> @@ -225,7 +225,7 @@ struct rte_eth_dev *
> > > > > > >>>>>>>>  		return NULL;
> > > > > > >>>>>>>>  	}
> > > > > > >>>>>>>>
> > > > > > >>>>>>>> -	memset(&rte_eth_devices[port_id], 0, sizeof(*eth_dev->data));
> > > > > > >>>>>>>> +	memset(&rte_eth_dev_data[port_id], 0, sizeof(struct rte_eth_dev_data));
> > > > > > >>>>>>>
> > > > > > >>>>>>> Not directly related to the this issue, but, after fix, this may have
> > > > > > >>>>>>> issues with secondary process.
> > > > > > >>>>>>>
> > > > > > >>>>>>> There were patches sent to fix this.
> > > > > > >>>>>>
> > > > > > >>>>>> I mean this one:
> > > > > > >>>>>> http://dpdk.org/ml/archives/dev/2017-January/054422.html
> > > > > > >>>>>
> > > > > > >>>>> d948f596fee2 ("ethdev: fix port data mismatched in multiple process
> > > > > > >>>>> model") should have fixed it.
> > > > > > >>>>
> > > > > > >>>> Think about case, where secondary process uses a virtual PMD, which does
> > > > > > >>>> a rte_eth_dev_allocate() call, shouldn't this corrupt primary process
> > > > > > >>>> device data?
> > > > > > >>>
> > > > > > >>> Yes, it may. However, I doubt that's the typical usage.
> > > > > > >>
> > > > > > >> But this is a use case, and broken now,
> > > > > > >
> > > > > > > I thought it was broken since the beginning?
> > > > > >
> > > > > > No, memset(&rte_eth_dev_data[port_id], ...) breaks it.
> > > > >
> > > > > Oh, you were talking about that particular case Remy's patch meant to
> > > > > fix.
> > > > >
> > > > > > >> and fix is known.
> > > > > > >
> > > > > > > And there is already a fix?
> > > > > >
> > > > > > http://dpdk.org/ml/archives/dev/2017-January/054422.html
> > > > >
> > > > > Yes, it should fix that issue.
> > > >
> > > > Well, few more thoughts: it may fix the crash issue Remy saw, but it
> > > > looks like more a workaround to me. Basically, if primary and secondary
> > > > shares a same port id, they should point to same device. Otherwise,
> > > > primary process may use eth_dev->data for a device A, while the
> > > > secondary process may use it for another device, as you said, it
> > > > could be a vdev.
> > > >
> > > > In such case, there is no way we could continue safely. That said,
> > > > the given patch avoids the total reset of eth_dev->data, while it
> > > > continues reset the eth_dev->data->name, which is wrong.
> > > >
> > > > So it's not a proper fix.
> > > >
> > > > Again, I think it's more about the usage. If primary starts with
> > > > a nic device A, while the secondary starts with a nic device B,
> > > > there is no way they could work well (unless they use different
> > > > port id).
> > >
> > > Why not?
> > > I think this is possible.
> > 
> > Yes, it's possible: find another port id if that one is already taken
> > by primary process (or even by secondary process: think that primary
> > process might attatch a port later).
> > 
> > > They just need to be initialized properly,
> > > so each rte_eth_devices[port_id]->data, etc. point to the right place.
> > 
> > My understanding is, as far as they use different port_id, it might
> > be fine. Just not sure it's enough or not.
> 
> As I understand, the main problem is that  rte_eth_devices[] is local,
> while rte_eth_dev_data points to the shared memory array.
> And rte_eth_dev_allocate() assumes that if rte_eth_devices[x] is free,
> then rte_eth_dev_data[port_id] is also free.
> Which is wrong in case when primary/secondary processes have different devices attached.
> Another problem is that inside rte_ethdev.c we manipulate rte_eth_dev_data[]
> contents without grabbing any lock.

Yes there are a lot of problems with the multiproc mode because it has
been implemented as a hack.
We are fixing some cases without figuring the whole picture.

I'll apply the patch from Remy which fixes a case where process creates
vdev (local data) and, hopefully, primary does no hotplug of PCI dev.

I'll restart this discussion with a bigger picture of what multiproc is,
and what are the issues.