[ltt-dev] [PATCH RFC urcu 1/2] Provide pthread_atfork-friendly interfaces

[Paul E. McKenney]

Provides call_rcu_before_fork() and call_rcu_after_fork_parent() to
go with the existing call_rcu_after_fork_child().

Signed-off-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
---
 README          |    4 ++++
 urcu-call-rcu.c |   29 ++++++++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletions(-)

diff --git a/README b/README
index f7f0dec..56e98d7 100644
--- a/README
+++ b/README
@@ -204,3 +204,7 @@ Interaction with fork()
 	liburcu-bp, which is designed to handle fork() by calling
 	rcu_bp_before_fork, rcu_bp_after_fork_parent and
 	rcu_bp_after_fork_child.
+
+	Applications that use call_rcu() are required to invoke
+	call_rcu_after_fork_child() from the child process after a
+	successful fork() system call that is not followed by exec().
diff --git a/urcu-call-rcu.c b/urcu-call-rcu.c
index bb56dbb..665f20c 100644
--- a/urcu-call-rcu.c
+++ b/urcu-call-rcu.c
@@ -566,13 +566,40 @@ void free_all_cpu_call_rcu_data(void)
 }
 
 /*
+ * Acquire the call_rcu_mutex in order to ensure that the child sees
+ * all of the call_rcu() data structures in a consistent state.
+ * Suitable for pthread_atfork() and friends.
+ */
+void call_rcu_before_fork(void)
+{
+	call_rcu_lock(&call_rcu_mutex);
+}
+
+/*
+ * Clean up call_rcu data structures in the parent of a successful fork()
+ * that is not followed by exec() in the child.  Suitable for
+ * pthread_atfork() and friends.
+ */
+void call_rcu_after_fork_parent(void)
+{
+	call_rcu_unlock(&call_rcu_mutex);
+}
+
+/*
  * Clean up call_rcu data structures in the child of a successful fork()
- * that is not followed by exec().
+ * that is not followed by exec().  Suitable for pthread_atfork() and
+ * friends.
  */
 void call_rcu_after_fork_child(void)
 {
 	struct call_rcu_data *crdp;
 
+	/* Re-initialize the mutex. */
+	if (pthread_mutex_init(&call_rcu_mutex, NULL) != 0) {
+		perror("pthread_mutex_init");
+		exit(-1);
+	}
+
 	/*
 	 * Allocate a new default call_rcu_data structure in order
 	 * to get a working call_rcu thread to go with it.
-- 
1.7.3.2