zebra: set SELECTED before going into dplane code

There is a bit of an impedance mismatch in the sequence of events here.
Depending on the dplane behavior, the `ROUTE_ENTRY_SELECTED` bit will be
inconsistent for rib_process_result().

With an asynchronous dataplane:
0. rib_process() is called
1. rib_install_kernel() is called, dplane action is queued
2. rib_install_kernel() returns
3. rib_process() sets the SELECTED bit appropriately, returns
4. dplane is done, triggers rib_process_result()
5. SELECTED bit is seen in "after" state
(5a. NHT code looks at the SELECTED bit, works correctly.)

With a synchronous dataplane:
0. rib_process() is called
1. rib_install_kernel() is called, dplane action is executed
2. dplane (should) trigger rib_process_result()
3. SELECTED bit is seen in "before" state
(3a. NHT code looks at the SELECTED bit, fails.)
4. rib_install_kernel() returns
5. rib_process() sets the SELECTED bit appropriately, too late.

Essentially, poking the dataplane is a sequencing point where control is
handed over to the dplane.  Control may or may not return immediately.
Doing /anything/ after triggering the dataplane is a recipe for odd race
conditions.

(FWIW, I'm not sure rib_process_result() is called correctly in the
synchronous case, but that's a separate problem.)

Unfortunately, this change might have some unforeseen side effects.  I
haven't dug through the code to see if anything breaks.  There
/shouldn't/ be anything looking at the SELECTED bit here, but who knows.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

0 files changed, 0 insertions, 0 deletions