[lttng-dev] [lttng-tools PATCH] Quick fix for Bug #7

[David Goulet]

Temporary fix the bug #7 issue for the 2.0 stable release. Refer to
bugs.lttng.org for more information on the issues.

The real stable fix is planned for 2.1+ stable release.

Signed-off-by: David Goulet <dgoulet at efficios.com>
---
 src/bin/lttng-sessiond/ust-app.c |   36 +++++++++++++++++++++++++++++++++++-
 src/common/hashtable/hashtable.c |    2 --
 src/common/hashtable/hashtable.h |    2 ++
 3 files changed, 37 insertions(+), 3 deletions(-)

diff --git a/src/bin/lttng-sessiond/ust-app.c b/src/bin/lttng-sessiond/ust-app.c
index 2b66b92..e82d38a 100644
--- a/src/bin/lttng-sessiond/ust-app.c
+++ b/src/bin/lttng-sessiond/ust-app.c
@@ -29,6 +29,9 @@
 
 #include <common/common.h>
 
+/* For add_unique_ust_app quick fix function for 2.0 stable release */
+#include <common/hashtable/hashtable.h>
+
 #include "ust-app.h"
 #include "ust-consumer.h"
 #include "ust-ctl.h"
@@ -1257,6 +1260,31 @@ error:
 }
 
 /*
+ * TEMP function call to add uniquely a registered apps to a hash table.
+ *
+ * If a duplicate node is found when adding apps, we delete the old one and
+ * close the socket file descriptor as well. Must be inside a read side lock.
+ *
+ * Please refer to BUG #7 on bugs.lttng.org to understand the purpose and
+ * lifespan of this function.
+ */
+static void add_unique_ust_app(struct lttng_ht *ht,
+		struct lttng_ht_node_ulong *node)
+{
+	struct cds_lfht_node *node_ptr;
+	struct lttng_ht_node_ulong *old_node;
+
+	node_ptr = cds_lfht_add_unique(ht->ht,
+			ht->hash_fct((void *) node->key, HASH_SEED), ht->match_fct,
+			(void *) node->key, &node->node);
+	if (node_ptr != &node->node) {
+		/* Double registration with same PID */
+		old_node = caa_container_of(node_ptr, struct lttng_ht_node_ulong, node);
+		call_rcu(&old_node->head, delete_ust_app_rcu);
+	}
+}
+
+/*
  * Using pid and uid (of the app), allocate a new ust_app struct and
  * add it to the global traceable app list.
  *
@@ -1307,7 +1335,13 @@ int ust_app_register(struct ust_register_msg *msg, int sock)
 
 	rcu_read_lock();
 	lttng_ht_add_unique_ulong(ust_app_sock_key_map, &lta->key.node);
-	lttng_ht_add_unique_ulong(ust_app_ht, &lta->node);
+	/*
+	 * Changed for now. Refer to BUG #7 called "Double PID registering and
+	 * unregistering race"
+	 *
+	 * lttng_ht_add_unique_ulong(ust_app_ht, &lta->node);
+	 */
+	add_unique_ust_app(ust_app_ht, &lta->node);
 	rcu_read_unlock();
 
 	DBG("App registered with pid:%d ppid:%d uid:%d gid:%d sock:%d name:%s"
diff --git a/src/common/hashtable/hashtable.c b/src/common/hashtable/hashtable.c
index 2080107..83d4dfd 100644
--- a/src/common/hashtable/hashtable.c
+++ b/src/common/hashtable/hashtable.c
@@ -27,8 +27,6 @@
 #include "hashtable.h"
 #include "utils.h"
 
-#define HASH_SEED            0x42UL		/* The answer to life */
-
 static unsigned long min_hash_alloc_size = 1;
 static unsigned long max_hash_buckets_size = (1UL << 20);
 
diff --git a/src/common/hashtable/hashtable.h b/src/common/hashtable/hashtable.h
index 1c2889d..0f0339c 100644
--- a/src/common/hashtable/hashtable.h
+++ b/src/common/hashtable/hashtable.h
@@ -23,6 +23,8 @@
 #include "rculfhash.h"
 #include "rculfhash-internal.h"
 
+#define HASH_SEED            0x42UL		/* The answer to life */
+
 typedef unsigned long (*hash_fct)(void *_key, unsigned long seed);
 typedef cds_lfht_match_fct hash_match_fct;
 
-- 
1.7.9