Re: [PATCH net-next] net/core: ensure features get disabled on new lower devs

From: Jarod Wilson
Date: Tue Nov 03 2015 - 17:12:03 EST

Alexander Duyck wrote:
On 11/03/2015 12:36 PM, Jarod Wilson wrote:
With moving netdev_sync_lower_features() after the .ndo_set_features
calls, I neglected to verify that devices added *after* a flag had been
disabled on an upper device were properly added with that flag
disabled as
well. This currently happens, because we exit __netdev_update_features()
when we see dev->features == features for the upper dev. We can retain
optimization of leaving without calling .ndo_set_features with a bit of
tweaking and a goto here.

Changing err to ret was somewhat arbitrary and makes the patch look more
involved, but seems to better fit the altered use.
+ if (!ret) {
+ dev->features = features;
+ ret = 1;
+ }

I would take the "ret = 1;" out of the if statement and let it stay here
by itself. Technically anything that traversed this path was returning 1
previously so we probably want to retain that behavior.

Ah, that. I took a look at all the callers of __netdev_update_features, and most don't even check return value, the one that does (netdev_update_features) only cares if its zero or not zero, so I figured it didn't really matter here, but it would indeed return 2 now instead of 1, if it got that from ndo_set_features. For consistency's sake, I can respin and just always set ret = 1 though.

/* some features must be disabled on lower devices when disabled
* on an upper device (think: bonding master or bridge)
netdev_for_each_lower_dev(dev, lower, iter)
netdev_sync_lower_features(dev, lower, features);

- if (!err)
- dev->features = features;

You could just alter the if statement here to check for a non-zero ret
value since you should have it as either 0 or 1. It shouldn't have any
other values.

That way you will have disabled the feature on the lower devices before
advertising that it has been disabled on the upper device.

If this check is down here, the goto will trigger, setting dev->features = features, but then, we got there because dev->features == features already, so meh. But it would also NOT trigger in the case of ndo_set_features returning 0 anymore, because we set ret = 1. Or am I missing something or misunderstanding what you're suggesting here?

Jarod Wilson

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