Currently this simplified code snippet fails:
br_vlan_get_pvid(netdev, &pvid);
br_vlan_get_info(netdev, pvid, &vinfo);
ASSERT(!(vinfo.flags & BRIDGE_VLAN_INFO_PVID));
It is intuitive that the pvid of a netdevice should have the
BRIDGE_VLAN_INFO_PVID flag set.
However I can't seem to pinpoint a commit where this behavior was
introduced. It seems like it's been like that since forever.
At a first glance it would make more sense to just handle the
BRIDGE_VLAN_INFO_PVID flag in __vlan_add_flags. However, as Nikolay
explains:
There are a few reasons why we don't do it, most importantly because
we need to have only one visible pvid at any single time, even if it's
stale - it must be just one. Right now that rule will not be violated
by this change, but people will try using this flag and could see two
pvids simultaneously. You can see that the pvid code is even using
memory barriers to propagate the new value faster and everywhere the
pvid is read only once. That is the reason the flag is set
dynamically when dumping entries, too. A second (weaker) argument
against would be given the above we don't want another way to do the
same thing, specifically if it can provide us with two pvids (e.g. if
walking the vlan list) or if it can provide us with a pvid different
from the one set in the vg. [Obviously, I'm talking about RCU
pvid/vlan use cases similar to the dumps. The locked cases are fine.
I would like to avoid explaining why this shouldn't be relied upon
without locking]
So instead of introducing the above change and making sure of the pvid
uniqueness under RCU, simply dynamically populate the pvid flag in
br_vlan_get_info().
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
f40d9b2086