Re: [PATCH v3 net-next 10/12] net: bonding: ensure .ndo_get_stats64 can sleep

[Vladimir Oltean <olteanv@gmail.com>]

On Thu, Jan 07, 2021 at 12:18:28PM +0100, Eric Dumazet wrote:
> What a mess really.

Thanks, that's at least _some_ feedback :)

> You chose to keep the assumption that ndo_get_stats() would not fail,
> since we were providing the needed storage from callers.
>
> If ndo_get_stats() are now allowed to sleep, and presumably allocate
> memory, we need to make sure
> we report potential errors back to the user.
>
> I think your patch series is mostly good, but I would prefer not
> hiding errors and always report them to user space.
> And no, netdev_err() is not appropriate, we do not want tools to look
> at syslog to guess something went wrong.

Well, there are only 22 dev_get_stats callers in the kernel, so I assume
that after the conversion to return void, I can do another conversion to
return int, and then I can convert the ndo_get_stats64 method to return
int too. I will keep the plain ndo_get_stats still void (no reason not
to).

> Last point about drivers having to go to slow path, talking to
> firmware : Make sure that malicious/innocent users
> reading /proc/net/dev from many threads in parallel wont brick these devices.
>
> Maybe they implicitly _relied_ on the fact that firmware was gently
> read every second and results were cached from a work queue or
> something.

How? I don't understand how I can make sure of that.

There is an effort initiated by Jakub to standardize the ethtool
statistics. My objection was that you can't expect that to happen unless
dev_get_stats is sleepable just like ethtool -S is. So I think the same
reasoning should apply to ethtool -S too, really.