neighbor: Fix state check in neigh_forced_gc

PERMANENT entries are not on the gc_list so the state check is now
redundant. Also, the move to not purge entries until after 5 seconds
should not apply to FAILED entries; those can be removed immediately
to make way for newer ones. This restores the previous logic prior to
the gc_list.

Fixes: 5895631 ("neighbor: Improve garbage collection")
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/neighbour.c

@@ -204,7 +204,6 @@ static int neigh_forced_gc(struct neigh_table *tbl)
 	unsigned long tref = jiffies - 5 * HZ;
 	u8 flags = NTF_EXT_LEARNED;
 	struct neighbour *n, *tmp;
-	u8 state = NUD_PERMANENT;
 	int shrunk = 0;
 
 	NEIGH_CACHE_STAT_INC(tbl, forced_gc_runs);
@@ -216,8 +215,8 @@ static int neigh_forced_gc(struct neigh_table *tbl)
 			bool remove = false;
 
 			write_lock(&n->lock);
-			if (!(n->nud_state & state) && !(n->flags & flags) &&
-			    time_after(tref, n->updated))
+			if ((n->nud_state == NUD_FAILED) ||
+			    (!(n->flags & flags) && time_after(tref, n->updated)))
 				remove = true;
 			write_unlock(&n->lock);