Re: [PATCH net-next] netdevsim: Register and unregister devlink traps on probe/remove device

On Mon, Oct 25, 2021 at 08:34:55AM +0300, Leon Romanovsky wrote:

On Sun, Oct 24, 2021 at 01:48:25PM +0300, Ido Schimmel wrote:

quoted

On Sun, Oct 24, 2021 at 12:54:52PM +0300, Leon Romanovsky wrote:

quoted

On Sun, Oct 24, 2021 at 12:05:12PM +0300, Ido Schimmel wrote:

quoted

On Sun, Oct 24, 2021 at 11:42:11AM +0300, Leon Romanovsky wrote:

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From: Leon Romanovsky <leonro@nvidia.com>

Align netdevsim to be like all other physical devices that register and
unregister devlink traps during their probe and removal respectively.

No, this is incorrect. Out of the three drivers that support both reload
and traps, both netdevsim and mlxsw unregister the traps during reload.
Here is another report from syzkaller about mlxsw [1].

Sorry, I overlooked it.

quoted

Please revert both 22849b5ea595 ("devlink: Remove not-executed trap
policer notifications") and 8bbeed485823 ("devlink: Remove not-executed
trap group notifications").

However, before we rush and revert commit, can you please explain why
current behavior to reregister traps on reload is correct?

I think that you are not changing traps during reload, so traps before
reload will be the same as after reload, am I right?

During reload we tear down the entire driver and load it again. As part
of the reload_down() operation we tear down the various objects from
both devlink and the device (e.g., shared buffer, ports, traps, etc.).
As part of the reload_up() operation we issue a device reset and
register everything back.

This is an implementation which is arguably questionable and pinpoints
problem with devlink reload. It mixes different SW layers into one big
mess which I tried to untangle.

The devlink "feature" that driver reregisters itself again during execution
of other user-visible devlink command can't be right design.

quoted

While the list of objects doesn't change, their properties (e.g., shared
buffer size, trap action, policer rate) do change back to the default
after reload and we cannot go back on that as it's a user-visible
change.

I don't propose to go back, just prefer to see fixed mlxsw that
shouldn't touch already created and registered objects from net/core/devlink.c.

All reset-to-default should be performed internally to the driver
without any need to devlink_*_register() again, so we will be able to
clean rest devlink notifications.

So at least for the netdevsim, this change looks like the correct one,
while mlxsw should be fixed next.

No, it's not correct. After your patch, trap properties like action are
not set back to the default. Regardless of what you think is the "right
design", you cannot introduce such regressions.

Calling devlink_*_unregister() in reload_down() and devlink_*_register()
in reload_up() is not new. It is done for multiple objects (e.g., ports,
regions, shared buffer, etc). After your patch, netdevsim is still doing
it.

Again, please revert the two commits I mentioned. If you think they are
necessary, you can re-submit them in the future, after proper review and
testing of the affected code paths.

Thanks