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

On Thu, Jan 7, 2021 at 10:51 AM Vladimir Oltean [off-list ref] wrote:

From: Vladimir Oltean <vladimir.oltean@nxp.com>

-

 static void bond_get_stats(struct net_device *bond_dev,
                           struct rtnl_link_stats64 *stats)
 {
        struct bonding *bond = netdev_priv(bond_dev);
-       struct rtnl_link_stats64 temp;
-       struct list_head *iter;
-       struct slave *slave;
-       int nest_level = 0;
+       struct rtnl_link_stats64 *dev_stats;
+       struct net_device **slaves;
+       int i, res, num_slaves;

+       res = bond_get_slave_arr(bond, &slaves, &num_slaves);
+       if (res) {
+               netdev_err(bond->dev,
+                          "failed to allocate memory for slave array\n");
+               return;
+       }

What a mess really.

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.

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.

Thanks.