Merge branch 'ipv6-fixes-for-RTF_CACHE-entries'

Paolo Abeni says:

====================
ipv6: fixes for RTF_CACHE entries

This series addresses 2 different but related issues with RTF_CACHE
introduced by the recent refactory.

patch 1 restore the gc timer for such routes
patch 2 removes the aged out dst from the fib tree, properly coping with pMTU
routes

v1 -> v2:
 - dropped the  for ip route show cache
 - avoid touching dst.obsolete when the dst is aged out

v2 -> v3:
 - take care of pMTU exceptions
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -1340,8 +1340,10 @@ out:
 	spin_unlock_bh(&rt6_exception_lock);
 
 	/* Update fn->fn_sernum to invalidate all cached dst */
-	if (!err)
+	if (!err) {
 		fib6_update_sernum(ort);
+		fib6_force_start_gc(net);
+	}
 
 	return err;
 }
@@ -1573,7 +1575,13 @@ static void rt6_age_examine_exception(struct rt6_exception_bucket *bucket,
 {
 	struct rt6_info *rt = rt6_ex->rt6i;
 
-	if (atomic_read(&rt->dst.__refcnt) == 1 &&
+	/* we are pruning and obsoleting aged-out and non gateway exceptions
+	 * even if others have still references to them, so that on next
+	 * dst_check() such references can be dropped.
+	 * EXPIRES exceptions - e.g. pmtu-generated ones are pruned when
+	 * expired, independently from their aging, as per RFC 8201 section 4
+	 */
+	if (!(rt->rt6i_flags & RTF_EXPIRES) &&
 	    time_after_eq(now, rt->dst.lastuse + gc_args->timeout)) {
 		RT6_TRACE("aging clone %p\n", rt);
 		rt6_remove_exception(bucket, rt6_ex);
@@ -1593,6 +1601,10 @@ static void rt6_age_examine_exception(struct rt6_exception_bucket *bucket,
 			rt6_remove_exception(bucket, rt6_ex);
 			return;
 		}
+	} else if (__rt6_check_expired(rt)) {
+		RT6_TRACE("purging expired route %p\n", rt);
+		rt6_remove_exception(bucket, rt6_ex);
+		return;
 	}
 	gc_args->more++;
 }