[PATCH net-next] neighbour: force neigh_invalidate when NUD_FAILED update is from admin

[Roopa Prabhu <roopa@cumulusnetworks.com>]

From: Roopa Prabhu <roopa@cumulusnetworks.com>

In systems where neigh gc thresh holds are set to high values,
admin deleted neigh entries (eg ip neigh flush or ip neigh del) can
linger around in NUD_FAILED state for a long time until periodic gc kicks
in. This patch forces neigh_invalidate when NUD_FAILED neigh_update is
from an admin.

Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com>
---
My testing has not shown any problems with this patch. But i
am not sure why historically neigh admin was not considered here:
I am assuming that it is because the problem is not very obvious in
default low gc threshold deployments.
 net/core/neighbour.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 8e3fda9..cbe85d8 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1148,7 +1148,8 @@ int neigh_update(struct neighbour *neigh, const u8 *lladdr, u8 new,
 		neigh->nud_state = new;
 		err = 0;
 		notify = old & NUD_VALID;
-		if ((old & (NUD_INCOMPLETE | NUD_PROBE)) &&
+		if (((old & (NUD_INCOMPLETE | NUD_PROBE)) ||
+		     (flags & NEIGH_UPDATE_F_ADMIN)) &&
 		    (new & NUD_FAILED)) {
 			neigh_invalidate(neigh);
 			notify = 1;
-- 
2.1.4