Re: [dpdk-dev] [dpdk-stable] [PATCH v3 1/7] ethdev: fix port data reset timing

[Matan Azrad <matan@mellanox.com>]

Hi Ferruh

 From: Ferruh Yigit, Wednesday, April 25, 2018 3:54 PM
> On 4/25/2018 1:16 PM, Matan Azrad wrote:
> > Hi all
> >
> > From: Ferruh Yigit, Thursday, April 19, 2018 2:08 PM
> >>> But rte_eth_dev_release_port() is still broken because of this
> >>> change, please check _rte_eth_dev_callback_process() which uses
> >>> dev->data- port_id.
> >
> > The issue is that a DESTROY callback gets port_id=0 all the time, regardless
> the destroyed port id.
> >
> > Let's discuss about the fix:
> >
> > There are 2 options for the DESTROY event meaning:
> >
> > 1. The device is going to be destroyed in the future (a bit after the callbacks
> calling).
> > 	The user may think that there is a valid data in the device structure in
> the callback time,
> > 	Thus, he may use it.
> > 	The fix here is to move the callback to the start of the function,
> > 	In this time the data field is still valid.
> >
> > 2. The device was already destroyed in the past (a bit before the callbacks
> calling).
> > 	The user should think that there is no any valid data in the device
> structure in the callback time,
> > 	Thus, he doesn't use it.
> > 	The issue here:
> > 	_rte_eth_dev_callback_process() assumes there is a valid data in the
> data field  all the time,
> > 	But in this case the data field is not valid because the device was
> already destroyed.
> > 	Optional fixes:
> > 	1. Always keep the data->port_id valid.
> > 	2. keep the data->port_id valid only for the
> _rte_eth_dev_callback_process() call.
> > 	3. Change _rte_eth_dev_callback_process() arg from "struct
> rte_eth_dev *dev" to "uint16_t port_id"
> > 		a. Need to change all the calls for this internal API.
> >
> > I vote to 2.1.
> >
> >
> > What do you think?
> 
> What is the concern with 1? It is easy to implement.
> 
Yes, also 2.1 and 2.2 are easy.

> And it may be better because if callback called after device destroyed, there
> is no guarantee/locking that same port won't be re-used, in the middle of the
> callback function rte_eth_dev_data can be updated, no?
> 

Good point!

I think we must guarantee no port allocation for the same port id in the callback time.
I also prefer to not call the callbacks in the critical section.

So maybe call it before the locking is better.