[dpdk-dev] [PATCH 2/2] eal: fix hang in ctrl thread creation error logic

[Luc Pelletier <lucp.at.work@gmail.com>]

The affinity of a control thread is set after it has been launched. If
setting the affinity fails, pthread_cancel is called followed by a call
to pthread_join, which can hang forever if the thread's start routine
doesn't call a pthread cancellation point.

This patch modifies the logic so that the control thread exits
gracefully if the affinity cannot be set successfully and removes the
call to pthread_cancel.

Fixes: 6383d26 ("eal: set name when creating a control thread")
Cc: olivier.matz@6wind.com
Cc: stable@dpdk.org

Signed-off-by: Luc Pelletier <lucp.at.work@gmail.com>
---

Hi Olivier,
Hi Honnappa,

As discussed, I've split the changes into 2 patches. This second commit
removes the pthread_cancel call which could result in a hang on join, if
the ctrl thread routine didn't call a cancellation point.

 lib/librte_eal/common/eal_common_thread.c | 29 +++++++++++++----------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_thread.c b/lib/librte_eal/common/eal_common_thread.c
index 3347e91bf..03dbcd9e8 100644
--- a/lib/librte_eal/common/eal_common_thread.c
+++ b/lib/librte_eal/common/eal_common_thread.c
@@ -187,14 +187,18 @@ static void *ctrl_thread_init(void *arg)
 		eal_get_internal_configuration();
 	rte_cpuset_t *cpuset = &internal_conf->ctrl_cpuset;
 	struct rte_thread_ctrl_params *params = arg;
-	void *(*start_routine)(void *) = params->start_routine;
+	void *(*start_routine)(void *);
 	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)
+		return NULL;
+
 	return start_routine(routine_arg);
 }
 
@@ -218,14 +222,12 @@ rte_ctrl_thread_create(pthread_t *thread, const char *name,
 	params->refcnt = 2;
 
 	ret = pthread_barrier_init(&params->configured, NULL, 2);
-	if (ret != 0) {
-		free(params);
-		return -ret;
-	}
+	if (ret != 0)
+		goto fail_no_barrier;
 
 	ret = pthread_create(thread, attr, ctrl_thread_init, (void *)params);
 	if (ret != 0)
-		goto fail;
+		goto fail_with_barrier;
 
 	if (name != NULL) {
 		ret = rte_thread_setname(*thread, name);
@@ -236,19 +238,22 @@ rte_ctrl_thread_create(pthread_t *thread, const char *name,
 
 	ret = pthread_setaffinity_np(*thread, sizeof(*cpuset), cpuset);
 	if (ret != 0)
-		goto fail_cancel;
+		params->start_routine = NULL;
 
 	pthread_barrier_wait(&params->configured);
 	ctrl_params_free(params);
 
-	return 0;
+	if (ret != 0)
+		/* start_routine has been set to NULL above; */
+		/* ctrl thread will exit immediately */
+		pthread_join(*thread, NULL);
 
-fail_cancel:
-	pthread_cancel(*thread);
-	pthread_join(*thread, NULL);
+	return -ret;
 
-fail:
+fail_with_barrier:
 	pthread_barrier_destroy(&params->configured);
+
+fail_no_barrier:
 	free(params);
 
 	return -ret;
-- 
2.25.1