From 038fcf1c8b7716415235384de5dc47d07dc45b85 Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Mon, 27 Sep 2021 17:44:19 +0200
Subject: Locking route attributes cache

To access route attribute cache from multiple threads at once, we have
to lock the cache on writing. The route attributes data structures are
safe to read unless somebody tries to tamper with the cache itself.
---
 nest/rt-attr.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

(limited to 'nest/rt-attr.c')

diff --git a/nest/rt-attr.c b/nest/rt-attr.c
index f7e33d72..20f9835d 100644
--- a/nest/rt-attr.c
+++ b/nest/rt-attr.c
@@ -1281,9 +1281,16 @@ rta_lookup(rta *o)
     ea_normalize(o->eattrs);
 
   h = rta_hash(o);
+
+  RTA_LOCK;
+
   for(r=rta_hash_table[h & rta_cache_mask]; r; r=r->next)
     if (r->hash_key == h && rta_same(r, o))
-      return rta_clone(r);
+    {
+      atomic_fetch_add_explicit(&r->uc, 1, memory_order_acq_rel);
+      RTA_UNLOCK;
+      return r;
+    }
 
   r = rta_copy(o);
   r->hash_key = h;
@@ -1294,12 +1301,21 @@ rta_lookup(rta *o)
   if (++rta_cache_count > rta_cache_limit)
     rta_rehash();
 
+  RTA_UNLOCK;
   return r;
 }
 
 void
 rta__free(rta *a)
 {
+  RTA_LOCK;
+  if (atomic_load_explicit(&a->uc, memory_order_acquire))
+  {
+    /* Somebody has cloned this rta inbetween. This sometimes happens. */
+    RTA_UNLOCK;
+    return;
+  }
+
   ASSERT(rta_cache_count && a->cached);
   rta_cache_count--;
   *a->pprev = a->next;
@@ -1311,6 +1327,7 @@ rta__free(rta *a)
   ea_free(a->eattrs);
   a->cached = 0;
   sl_free(rta_slab(a), a);
+  RTA_UNLOCK;
 }
 
 rta *
@@ -1335,7 +1352,7 @@ rta_do_cow(rta *o, linpool *lp)
  * This function takes a &rta and dumps its contents to the debug output.
  */
 void
-rta_dump(rta *a)
+rta_dump(const rta *a)
 {
   static char *rts[] = { "", "RTS_STATIC", "RTS_INHERIT", "RTS_DEVICE",
 			 "RTS_STAT_DEV", "RTS_REDIR", "RTS_RIP",
@@ -1350,7 +1367,7 @@ rta_dump(rta *a)
     debug(" !CACHED");
   debug(" <-%I", a->from);
   if (a->dest == RTD_UNICAST)
-    for (struct nexthop *nh = &(a->nh); nh; nh = nh->next)
+    for (const struct nexthop *nh = &(a->nh); nh; nh = nh->next)
       {
 	if (ipa_nonzero(nh->gw)) debug(" ->%I", nh->gw);
 	if (nh->labels) debug(" L %d", nh->label[0]);
@@ -1377,6 +1394,8 @@ rta_dump_all(void)
   rta *a;
   uint h;
 
+  RTA_LOCK;
+
   debug("Route attribute cache (%d entries, rehash at %d):\n", rta_cache_count, rta_cache_limit);
   for(h=0; h<rta_cache_size; h++)
     for(a=rta_hash_table[h]; a; a=a->next)
@@ -1386,10 +1405,12 @@ rta_dump_all(void)
 	debug("\n");
       }
   debug("\n");
+
+  RTA_UNLOCK;
 }
 
 void
-rta_show(struct cli *c, rta *a)
+rta_show(struct cli *c, const rta *a)
 {
   cli_printf(c, -1008, "\tType: %s %s", rta_src_names[a->source], ip_scope_text(a->scope));
 
-- 
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