MINOR: proxy: use atomic ops for default proxy refcount

Default proxy refcount <def_ref> is used to comptabilize reference on a
default proxy instance by standard proxies. Currently, this is necessary
when a default proxy defines TCP/HTTP rules or a tcpcheck ruleset.

Transform every access on <def_ref> so that atomic operations are now
used. Currently, this is not strictly needed as default proxies
references are only manipulated at init or deinit in single thread mode.
However, when dynamic backends deletion will be implemented, <def_ref>
will be decremented at runtime also.

Author: a-denoyelle

src/proxy.c

@@ -3009,7 +3009,7 @@ void defaults_px_destroy_all_unref(void)
 	for (px = cebis_item_first(&defproxy_by_name, conf.name_node, id, struct proxy); px; px = nx) {
 		BUG_ON(!(px->cap & PR_CAP_DEF));
 		nx = cebis_item_next(&defproxy_by_name, conf.name_node, id, px);
-		if (!px->conf.def_ref)
+		if (!HA_ATOMIC_LOAD(&px->conf.def_ref))
 			defaults_px_destroy(px);
 	}
 }
@@ -3024,7 +3024,7 @@ void defaults_px_detach(struct proxy *px)
 {
 	BUG_ON(!(px->cap & PR_CAP_DEF));
 	cebis_item_delete(&defproxy_by_name, conf.name_node, id, px);
-	if (!px->conf.def_ref)
+	if (!HA_ATOMIC_LOAD(&px->conf.def_ref))
 		defaults_px_destroy(px);
 	/* If not destroyed, <px> can still be accessed in <defaults_list>. */
 }
@@ -3040,7 +3040,7 @@ void defaults_px_ref_all(void)
 	for (px = cebis_item_first(&defproxy_by_name, conf.name_node, id, struct proxy);
 	     px;
 	     px = cebis_item_next(&defproxy_by_name, conf.name_node, id, px)) {
-		++px->conf.def_ref;
+		HA_ATOMIC_INC(&px->conf.def_ref);
 	}
 }
 
@@ -3057,7 +3057,7 @@ void defaults_px_unref_all(void)
 		nx = cebis_item_next(&defproxy_by_name, conf.name_node, id, px);
 
 		BUG_ON(!px->conf.def_ref);
-		if (!--px->conf.def_ref)
+		if (!HA_ATOMIC_SUB_FETCH(&px->conf.def_ref, 1))
 			defaults_px_destroy(px);
 	}
 }
@@ -3066,8 +3066,7 @@ void defaults_px_unref_all(void)
  * done if <px> already references <defpx>. Otherwise, the default proxy
  * <def_ref> count is incremented by one.
  *
- * This operation is not thread safe. It must only be performed during init
- * stage or under thread isolation.
+ * Access on default proxy reference is thread safe thanks to atomic ops.
  */
 static inline void defaults_px_ref(struct proxy *defpx, struct proxy *px)
 {
@@ -3077,7 +3076,7 @@ static inline void defaults_px_ref(struct proxy *defpx, struct proxy *px)
 	BUG_ON(px->defpx);
 
 	px->defpx = defpx;
-	defpx->conf.def_ref++;
+	HA_ATOMIC_INC(&defpx->conf.def_ref);
 }
 
 /* Check that <px> can inherits from <defpx> default proxy. If some settings
@@ -3178,14 +3177,15 @@ int proxy_ref_defaults(struct proxy *px, struct proxy *defpx, char **errmsg)
 
 /* proxy <px> removes its reference on its default proxy. The default proxy
  * <def_ref> count is decremented by one. If it was the last reference, the
- * corresponding default proxy is destroyed. For now this operation is not
- * thread safe and is performed during deinit staged only.
-*/
+ * corresponding default proxy is destroyed.
+ *
+ * Access on default proxy reference is thread safe thanks to atomic ops.
+ */
 void proxy_unref_defaults(struct proxy *px)
 {
 	if (px->defpx == NULL)
 		return;
-	if (!--px->defpx->conf.def_ref)
+	if (!HA_ATOMIC_SUB_FETCH(&px->defpx->conf.def_ref, 1))
 		defaults_px_destroy(px->defpx);
 	px->defpx = NULL;
 }