[OpenWrt-Devel] [PATCH 3/3] netifd: Read current link state when processing netlink event

[Felix Fietkau]

On 2014-10-22 14:14, Hans Dedecker wrote:
> Netifd commit b2dcb02570939d98b92c7c55db1c328693a5d52a introduces
> a race condition resulting into infinite toggling interfaces
> (eg static interfaces with linksensing enabled, vlan interfaces
> with proto none (#18106)) when linksensing is enabled resulting into
> a crash.
> As netlink event messages will be queued on the netlink event socket
> the included lower up interface flag will not always represent the
> current link state when netifd processes the netlink messages;
> by reading the current link state when a netlink event message is
> parsed the correct info is passed to the device layer.
> This will avoid continuous interface toggling (down/up) triggered
> by link state changes based on outdated netlink interface info.
> This solution replaces the patch which was introduced to solve
> issue (#1806) for vlan devices as other protocol handlers suffered
> from the same problem.
> 
> Signed-off-by: Hans Dedecker <dedeckeh at gmail.com>
While I agree with the change to read the carrier directly, this patch
still has a remaining race condition.
I added keep_link_status, because the VLAN device event callbacks set
the VLAN device link status based on the link status of the parent device.
Please either leave in keep_link_status or remove link status handling
from the device event callbacks of VLAN devices.

- Felix
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