[dpdk-dev] [PATCH v4 1/2] eal: simplify the implementation of rte_ctrl_thread_create

[Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>]

Remove the usage of pthread barrier and replace it with
synchronization using atomic variable. This also removes
the use of reference count required to synchronize freeing
the memory.

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
---
v4:
1) Used rte_delay_us_sleep instead of sched_yield. Using sched_yield
   requires to maintain a Windows version of the rte_ctrl_thread_create
   API.

v3:
1) RFC to Patch
2) Changed commit log and API description [Olivier]
3) Used sched_yield while spinning [Stephen]
4) Fixed use after free
5) Added a test case

v2:
1) Used compiler's C++11 atomic built-ins to access the shared variable.

 lib/eal/common/eal_common_thread.c | 87 +++++++++++++++---------------
 lib/eal/include/rte_lcore.h        |  9 ++--
 2 files changed, 49 insertions(+), 47 deletions(-)

diff --git a/lib/eal/common/eal_common_thread.c b/lib/eal/common/eal_common_thread.c
index 1a52f42a2b..e8e4149f69 100644
--- a/lib/eal/common/eal_common_thread.c
+++ b/lib/eal/common/eal_common_thread.c
@@ -166,38 +166,44 @@ __rte_thread_uninit(void)
 	RTE_PER_LCORE(_lcore_id) = LCORE_ID_ANY;
 }
 
+enum __rte_ctrl_thread_status {
+	__RTE_CTRL_THREAD_LAUNCHING, /* Yet to call pthread_create function */
+	__RTE_CTRL_THREAD_RUNNING, /* Control thread is running successfully */
+	__RTE_CTRL_THREAD_ERROR /* Control thread encountered an error */
+};
+
 struct rte_thread_ctrl_params {
 	void *(*start_routine)(void *);
 	void *arg;
-	pthread_barrier_t configured;
-	unsigned int refcnt;
+	int ret;
+	/* Control thread status. If the status is __RTE_CTRL_THREAD_ERROR
+	 * 'ret' has the error code.
+	 */
+	enum __rte_ctrl_thread_status ctrl_thread_status;
 };
 
-static void ctrl_params_free(struct rte_thread_ctrl_params *params)
-{
-	if (__atomic_sub_fetch(&params->refcnt, 1, __ATOMIC_ACQ_REL) == 0) {
-		(void)pthread_barrier_destroy(&params->configured);
-		free(params);
-	}
-}
-
 static void *ctrl_thread_init(void *arg)
 {
 	struct internal_config *internal_conf =
 		eal_get_internal_configuration();
 	rte_cpuset_t *cpuset = &internal_conf->ctrl_cpuset;
 	struct rte_thread_ctrl_params *params = arg;
-	void *(*start_routine)(void *);
+	void *(*start_routine)(void *) = params->start_routine;
 	void *routine_arg = params->arg;
 
 	__rte_thread_init(rte_lcore_id(), cpuset);
-
-	pthread_barrier_wait(&params->configured);
-	start_routine = params->start_routine;
-	ctrl_params_free(params);
-
-	if (start_routine == NULL)
+	params->ret = pthread_setaffinity_np(pthread_self(),
+				sizeof(*cpuset), cpuset);
+	if (params->ret != 0) {
+		__atomic_store_n(&params->ctrl_thread_status,
+					__RTE_CTRL_THREAD_ERROR,
+					__ATOMIC_RELEASE);
 		return NULL;
+	}
+
+	__atomic_store_n(&params->ctrl_thread_status,
+				__RTE_CTRL_THREAD_RUNNING,
+				__ATOMIC_RELEASE);
 
 	return start_routine(routine_arg);
 }
@@ -207,10 +213,8 @@ rte_ctrl_thread_create(pthread_t *thread, const char *name,
 		const pthread_attr_t *attr,
 		void *(*start_routine)(void *), void *arg)
 {
-	struct internal_config *internal_conf =
-		eal_get_internal_configuration();
-	rte_cpuset_t *cpuset = &internal_conf->ctrl_cpuset;
 	struct rte_thread_ctrl_params *params;
+	enum __rte_ctrl_thread_status ctrl_thread_status;
 	int ret;
 
 	params = malloc(sizeof(*params));
@@ -219,15 +223,14 @@ rte_ctrl_thread_create(pthread_t *thread, const char *name,
 
 	params->start_routine = start_routine;
 	params->arg = arg;
-	params->refcnt = 2;
-
-	ret = pthread_barrier_init(&params->configured, NULL, 2);
-	if (ret != 0)
-		goto fail_no_barrier;
+	params->ret = 0;
+	params->ctrl_thread_status = __RTE_CTRL_THREAD_LAUNCHING;
 
 	ret = pthread_create(thread, attr, ctrl_thread_init, (void *)params);
-	if (ret != 0)
-		goto fail_with_barrier;
+	if (ret != 0) {
+		free(params);
+		return -ret;
+	}
 
 	if (name != NULL) {
 		ret = rte_thread_setname(*thread, name);
@@ -236,24 +239,22 @@ rte_ctrl_thread_create(pthread_t *thread, const char *name,
 				"Cannot set name for ctrl thread\n");
 	}
 
-	ret = pthread_setaffinity_np(*thread, sizeof(*cpuset), cpuset);
-	if (ret != 0)
-		params->start_routine = NULL;
-
-	pthread_barrier_wait(&params->configured);
-	ctrl_params_free(params);
-
-	if (ret != 0)
-		/* start_routine has been set to NULL above; */
-		/* ctrl thread will exit immediately */
+	/* Wait for the control thread to initialize successfully */
+	while ((ctrl_thread_status =
+		__atomic_load_n(&params->ctrl_thread_status, __ATOMIC_ACQUIRE))
+		== __RTE_CTRL_THREAD_LAUNCHING)
+		/* Yield the CPU. Using sched_yield call requires maintaining
+		 * another implementation for Windows as sched_yield is not
+		 * supported on Windows.
+		 */
+		rte_delay_us_sleep(1);
+
+	/* Check if the control thread encountered an error */
+	if (ctrl_thread_status == __RTE_CTRL_THREAD_ERROR)
+		/* ctrl thread is exiting */
 		pthread_join(*thread, NULL);
 
-	return -ret;
-
-fail_with_barrier:
-	(void)pthread_barrier_destroy(&params->configured);
-
-fail_no_barrier:
+	ret = params->ret;
 	free(params);
 
 	return -ret;
diff --git a/lib/eal/include/rte_lcore.h b/lib/eal/include/rte_lcore.h
index 1550b75da0..b81c8b2685 100644
--- a/lib/eal/include/rte_lcore.h
+++ b/lib/eal/include/rte_lcore.h
@@ -420,10 +420,11 @@ rte_thread_unregister(void);
 /**
  * Create a control thread.
  *
- * Wrapper to pthread_create(), pthread_setname_np() and
- * pthread_setaffinity_np(). The affinity of the new thread is based
- * on the CPU affinity retrieved at the time rte_eal_init() was called,
- * the dataplane and service lcores are then excluded.
+ * Creates a control thread with the given name and attributes. The
+ * affinity of the new thread is based on the CPU affinity retrieved
+ * at the time rte_eal_init() was called, the dataplane and service
+ * lcores are then excluded. If setting the name of the thread fails,
+ * the error is ignored and a debug message is logged.
  *
  * @param thread
  *   Filled with the thread id of the new created thread.
-- 
2.25.1