Re: [dpdk-dev] [dpdk-stable] [PATCH 2/2] app/testpmd: fix invalid port detaching

[Thomas Monjalon <thomas@monjalon.net>]

Hi,

This discussion becomes confusing so I do a summary below.
I think we can do several fixes in 20.02.

12/02/2020 14:49, Ferruh Yigit:
> On 2/3/2020 5:10 PM, Matan Azrad wrote:

[stripping long discussion in favor of a summary below]

> > Even if the PMD clear the device pointer, the testpmd still may release wrong rte_device.
> 
> Yes it may, although that is less likely to occur, it requires a new device hot
> added between close() and detach of the other device.
> 
> Would you be agree to say there are two problems:
> 
> 1) When testpmd close a port, a new attached port can re-use it over writing
> some fields, relying the data structures of the closed port is not safe.
> 
> 2) PMD not cleaning ethdev->device pointer in the .remove() may cause issues in
> double detach of a port.
> 
> 
> For (1) I suggest fixing it in the attach path, don't re-use an eth_dev port id
> unless it is completely freed, may need to add new state for it. Does it make sense?

Yes we could add a CLOSED state which is set on ethdev close.
When the rte_device is freed, the PMD could set attached ports as UNUSED.
But given some ethdev ports can be open and closed dynamically,
I am not sure it is a good solution to keep them in CLOSED state and ask
PMD to remember them.

An alternative workaround could be to allocate port_id by incrementing
a saved biggest id. So the race condition would be very unlikely.
The drawbacks are having big port_id numbers and changing the id
allocation algorithm (which is not documented anyway).

The proposals above for port_id allocation or states rework cannot be
done in 20.02. Let's discuss and work on it in a separated thread.

> For (2) PMDs want to get hotplug support needs to fix it.

Yes PMDs should clear rte_eth_devices[port_id].device in .remove().

We must also protect from user calling detach on a closed port
by adding a check in cmd_operate_detach_port_parsed(),
before calling detach_port_device().

The hotplug rmv_port_callback() must be able to call detach after close.
There are three possible fixes:
	- revert the port_id_is_invalid() check in detach_port_device()
	- call rte_dev_remove(rte_device) directly
	- call a new function with rte_device (detach_port_device() can use it)

About the function detach_port_device() itself, yes this function is
strange to say the least. It was a convenience for detaching a rte_device
from a port_id.
The cleanup of siblings with RTE_ETH_FOREACH_DEV_OF(sibling, dev),
should probably be removed. I've added it as a temporary solution
before all PMDs are properly fixed:
	rte_eth_devices[sibling].device = NULL;

For info, there is a function detach_device() used by the command
	"device detach <identifier>"