1 files changed, 20 insertions, 14 deletions

diff --git a/nest/route.h b/nest/route.h
index 285fb372..c435b9e0 100644
--- a/nest/route.h
+++ b/nest/route.h
@@ -181,7 +181,7 @@ struct hostentry {
   ip_addr addr;				/* IP address of host, part of key */
   ip_addr link;				/* (link-local) IP address of host, used as gw
 					   if host is directly attached */
-  struct rtable *tab;			/* Dependent table, part of key*/
+  struct rtable *tab;			/* Dependent table, part of key */
   struct hostentry *next;		/* Next in hash chain */
   unsigned hash_key;			/* Hash key */
   unsigned uc;				/* Use count */
@@ -513,19 +513,25 @@ void rta_show(struct cli *, rta *, ea_list *);
 void rta_set_recursive_next_hop(rtable *dep, rta *a, rtable *tab, ip_addr *gw, ip_addr *ll);
 
 /*
- * rta_set_recursive_next_hop() acquires hostentry from hostcache and
- * fills rta->hostentry field.  New hostentry has zero use
- * count. Cached rta locks its hostentry (increases its use count),
- * uncached rta does not lock it. Hostentry with zero use count is
- * removed asynchronously during host cache update, therefore it is
- * safe to hold such hostentry temorarily. Hostentry holds a lock for
- * a 'source' rta, mainly to share multipath nexthops. There is no
- * need to hold a lock for hostentry->dep table, because that table
- * contains routes responsible for that hostentry, and therefore is
- * non-empty if given hostentry has non-zero use count. The protocol
- * responsible for routes with recursive next hops should also hold a
- * lock for a table governing that routes (argument tab to
- * rta_set_recursive_next_hop()).
+ * rta_set_recursive_next_hop() acquires hostentry from hostcache and fills
+ * rta->hostentry field.  New hostentry has zero use count. Cached rta locks its
+ * hostentry (increases its use count), uncached rta does not lock it. Hostentry
+ * with zero use count is removed asynchronously during host cache update,
+ * therefore it is safe to hold such hostentry temorarily. Hostentry holds a
+ * lock for a 'source' rta, mainly to share multipath nexthops.
+ *
+ * There is no need to hold a lock for hostentry->dep table, because that table
+ * contains routes responsible for that hostentry, and therefore is non-empty if
+ * given hostentry has non-zero use count. If the hostentry has zero use count,
+ * the entry is removed before dep is referenced.
+ *
+ * The protocol responsible for routes with recursive next hops should hold a
+ * lock for a 'source' table governing that routes (argument tab to
+ * rta_set_recursive_next_hop()), because its routes reference hostentries
+ * (through rta) related to the governing table. When all such routes are
+ * removed, rtas are immediately removed achieving zero uc. Then the 'source'
+ * table lock could be immediately released, although hostentries may still
+ * exist - they will be freed together with the 'source' table.
  */
 
 static inline void rt_lock_hostentry(struct hostentry *he) { if (he) he->uc++; }