utils_vl_lookup: Fixed a race when creating user objects.

This could cause multiple aggregation instances to be created in the
aggregation plugin when first writing data to the plugin. This, in turn, led
to "value too old" warnings because subsequently all data was submitted twice.

Thanks to @faxm0dem for reporting this in GH #535.

diff --git a/src/aggregation.c b/src/aggregation.c
index 0c0f19d..8175c66 100644 (file)
--- a/src/aggregation.c
+++ b/src/aggregation.c
@@ -440,8 +440,7 @@ static int agg_instance_read (agg_instance_t *inst, cdtime_t t) /* {{{ */
 
 /* lookup_class_callback_t for utils_vl_lookup */
 static void *agg_lookup_class_callback ( /* {{{ */
-    __attribute__((unused)) data_set_t const *ds,
-    value_list_t const *vl, void *user_class)
+    data_set_t const *ds, value_list_t const *vl, void *user_class)
 {
   return (agg_instance_create (ds, vl, (aggregation_t *) user_class));
 } /* }}} void *agg_class_callback */

diff --git a/src/utils_vl_lookup.c b/src/utils_vl_lookup.c
index 722c452..8180d0d 100644 (file)
--- a/src/utils_vl_lookup.c
+++ b/src/utils_vl_lookup.c
@@ -26,6 +26,7 @@
 
 #include "collectd.h"
 
+#include <pthread.h>
 #include <regex.h>
 
 #include "common.h"
@@ -86,6 +87,7 @@ struct user_obj_s
 
 struct user_class_s
 {
+  pthread_mutex_t lock;
   void *user_class;
   identifier_match_t match;
   user_obj_t *user_obj_list; /* list of user_obj */
@@ -191,6 +193,7 @@ static int lu_copy_ident_to_match (identifier_match_t *match, /* {{{ */
   return (0);
 } /* }}} int lu_copy_ident_to_match */
 
+/* user_class->lock must be held when calling this function */
 static void *lu_create_user_obj (lookup_t *obj, /* {{{ */
     data_set_t const *ds, value_list_t const *vl,
     user_class_t *user_class)
@@ -245,6 +248,7 @@ static void *lu_create_user_obj (lookup_t *obj, /* {{{ */
   return (user_obj);
 } /* }}} void *lu_create_user_obj */
 
+/* user_class->lock must be held when calling this function */
 static user_obj_t *lu_find_user_obj (user_class_t *user_class, /* {{{ */
     value_list_t const *vl)
 {
@@ -294,14 +298,17 @@ static int lu_handle_user_class (lookup_t *obj, /* {{{ */
       || !lu_part_matches (&user_class->match.host, vl->host))
     return (1);
 
+  pthread_mutex_lock (&user_class->lock);
   user_obj = lu_find_user_obj (user_class, vl);
   if (user_obj == NULL)
   {
     /* call lookup_class_callback_t() and insert into the list of user objects. */
     user_obj = lu_create_user_obj (obj, ds, vl, user_class);
+    pthread_mutex_unlock (&user_class->lock);
     if (user_obj == NULL)
       return (-1);
   }
+  pthread_mutex_unlock (&user_class->lock);
 
   status = obj->cb_user_obj (ds, vl,
       user_class->user_class, user_obj->user_obj);
@@ -402,7 +409,7 @@ static int lu_add_by_plugin (by_type_entry_t *by_type, /* {{{ */
   identifier_match_t const *match = &user_class_list->entry.match;
 
   /* Lookup user_class_list from the per-plugin structure. If this is the first
-   * user_class to be added, the blocks return immediately. Otherwise they will
+   * user_class to be added, the block returns immediately. Otherwise they will
    * set "ptr" to non-NULL. */
   if (match->plugin.is_regex)
   {
@@ -487,6 +494,7 @@ static void lu_destroy_user_class_list (lookup_t *obj, /* {{{ */
 
     lu_destroy_user_obj (obj, user_class_list->entry.user_obj_list);
     user_class_list->entry.user_obj_list = NULL;
+    pthread_mutex_destroy (&user_class_list->entry.lock);
 
     sfree (user_class_list);
     user_class_list = next;
@@ -599,6 +607,7 @@ int lookup_add (lookup_t *obj, /* {{{ */
     return (ENOMEM);
   }
   memset (user_class_obj, 0, sizeof (*user_class_obj));
+  pthread_mutex_init (&user_class_obj->entry.lock, /* attr = */ NULL);
   user_class_obj->entry.user_class = user_class;
   lu_copy_ident_to_match (&user_class_obj->entry.match, ident, group_by);
   user_class_obj->entry.user_obj_list = NULL;