Re: [PATCH v2] failsafe: fix segfault on hotplug event

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 10 Nov 2022 12:42:43 -0500
Luc Pelletier <lucp.at.work@gmail.com> wrote:

> When the failsafe PMD encounters a hotplug event, it switches its rx/tx
> functions to "safe" ones that validate the sub-device's rx/tx functions
> before calling them. It switches the rx/tx functions by changing the
> function pointers in the rte_eth_dev structure.
> 
> Following commit 7a0935239b9e, the rx/tx functions of PMDs are no longer
> called through the function pointers in the rte_eth_dev structure. They
> are rather called through a flat array named rte_eth_fp_ops. The
> function pointers in that array are initialized when the devices start
> and are initialized.
> 
> When a hotplug event occurs, the function pointers in rte_eth_fp_ops
> still point to the "unsafe" rx/tx functions in the failsafe PMD since
> they haven't been updated. This results in a segmentation fault because
> it ends up using the "unsafe" functions, when the "safe" functions
> should have been used.
> 
> To fix the problem, the failsafe PMD code was changed to update the
> function pointers in the rte_eth_fp_ops array when a hotplug event
> occurs.

Have it in both places might be breaking other drivers as well.
Shouldn't there be a ethdev function when changing rx/tx burst.

Also, changing a variable used by another thread needs to be
using __atomic_store and __atomic_load to guarantee that CPU
or compiler will no that it changed.