Re: [PATCH net 1/4] net-sysfs: check device is present when showing carrier

[Johannes Berg <johannes@sipsolutions.net>]

On Wed, 2024-07-24 at 11:35 +0200, Johannes Berg wrote:
> On Wed, 2024-07-24 at 01:46 +0000, Jamie Bainbridge wrote:
> > A sysfs reader can race with a device reset or removal.
> 
> Kind of, yes, but please check what the race actually is.
> 
> > This was fixed for speed_show with commit 4224cfd7fb65 ("net-sysfs: add
> > check for netdevice being present to speed_show") so add the same check
> > to carrier_show.
> 
> You didn't say why it's needed here, so ... why is it?
> 
> FWIW, I don't think it actually _is_ needed, since the netdev struct
> itself is still around, linkwatch_sync_dev() will not do anything that's
> not still needed anyway (the removal from list must clearly either still
> happen or nothing happens in the function). This will not call into the
> driver (which would be the problematic part).
> 
> So while I don't think this is _wrong_ per se, I also don't think it's
> necessary, nor are you demonstrating that it is.
> 
> And for userspace it should be pretty much immaterial whether it gets a
> real value or -EINVAL in the race, or -ENOENT because the file
> disappeared anyway?
> 

All of which, btw, is also true for patches 3 and 4 in this set.

For patch 2 it seems applicable.

I do wonder if ethtool itself, at least ethtool netlink, doesn't have a
similar problem though, since it just uses netdev_get_by_name() /
netdev_get_by_index()?

johannes