From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Sun, 8 Dec 2013 15:31:04 +0000 (-0500)
Subject: Fix: urcu-bp interaction with threads vs constructors/destructors
X-Git-Tag: v0.9.0~116
X-Git-Url: https://git.lttng.org/?p=urcu.git;a=commitdiff_plain;h=76d6a95136c6879dfc262b08aabf3c0a81126ffe

Fix: urcu-bp interaction with threads vs constructors/destructors

Add a reference counter for threads using urcu-bp, thus ensuring that
even if the urcu destructor is executed before each thread using RCU
read-side critical sections exit, those threads will not see a corrupted
thread list.

Also, don't use URCU_TLS() within urcu_bp_thread_exit_notifier(). It
appears that this is racy (although this was probably due to the issue
fixed by reference counting). Anyway, play safe, and pass the rcu_key
received as parameter instead.

Those issues only reproduce when threads are still active when the
urcu-bp destructor is called.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/urcu-bp.c b/urcu-bp.c
index 387a52b..369beba 100644
--- a/urcu-bp.c
+++ b/urcu-bp.c
@@ -91,6 +91,9 @@ void *mremap_wrapper(void *old_address, size_t old_size,
  */
 #define RCU_QS_ACTIVE_ATTEMPTS 100
 
+static
+int rcu_bp_refcount;
+
 static
 void __attribute__((constructor)) rcu_bp_init(void);
 static
@@ -454,11 +457,8 @@ struct registry_chunk *find_chunk(struct rcu_reader *rcu_reader_reg)
 
 /* Called with signals off and mutex locked */
 static
-void remove_thread(void)
+void remove_thread(struct rcu_reader *rcu_reader_reg)
 {
-	struct rcu_reader *rcu_reader_reg;
-
-	rcu_reader_reg = URCU_TLS(rcu_reader);
 	cleanup_thread(find_chunk(rcu_reader_reg), rcu_reader_reg);
 	URCU_TLS(rcu_reader) = NULL;
 }
@@ -499,7 +499,7 @@ end:
 
 /* Disable signals, take mutex, remove from registry */
 static
-void rcu_bp_unregister(void)
+void rcu_bp_unregister(struct rcu_reader *rcu_reader_reg)
 {
 	sigset_t newmask, oldmask;
 	int ret;
@@ -512,11 +512,12 @@ void rcu_bp_unregister(void)
 		abort();
 
 	mutex_lock(&rcu_gp_lock);
-	remove_thread();
+	remove_thread(rcu_reader_reg);
 	mutex_unlock(&rcu_gp_lock);
 	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 	if (ret)
 		abort();
+	rcu_bp_exit();
 }
 
 /*
@@ -526,15 +527,14 @@ void rcu_bp_unregister(void)
 static
 void urcu_bp_thread_exit_notifier(void *rcu_key)
 {
-	assert(rcu_key == URCU_TLS(rcu_reader));
-	rcu_bp_unregister();
+	rcu_bp_unregister(rcu_key);
 }
 
 static
 void rcu_bp_init(void)
 {
 	mutex_lock(&init_lock);
-	if (!initialized) {
+	if (!rcu_bp_refcount++) {
 		int ret;
 
 		ret = pthread_key_create(&urcu_bp_key,
@@ -549,16 +549,21 @@ void rcu_bp_init(void)
 static
 void rcu_bp_exit(void)
 {
-	struct registry_chunk *chunk, *tmp;
-	int ret;
+	mutex_lock(&init_lock);
+	if (!--rcu_bp_refcount) {
+		struct registry_chunk *chunk, *tmp;
+		int ret;
 
-	cds_list_for_each_entry_safe(chunk, tmp,
-			&registry_arena.chunk_list, node) {
-		munmap(chunk, chunk->data_len + sizeof(struct registry_chunk));
+		cds_list_for_each_entry_safe(chunk, tmp,
+				&registry_arena.chunk_list, node) {
+			munmap(chunk, chunk->data_len
+					+ sizeof(struct registry_chunk));
+		}
+		ret = pthread_key_delete(urcu_bp_key);
+		if (ret)
+			abort();
 	}
-	ret = pthread_key_delete(urcu_bp_key);
-	if (ret)
-		abort();
+	mutex_unlock(&init_lock);
 }
 
 /*