[PATCH v2] eal: fix thread race in control thread creation

[Tyler Retzlaff <roretzla@linux.microsoft.com>]

When ctrl_thread_init transitions params->ctrl_thread_status from
CTRL_THREAD_LAUNCHING the creating thread and new thread may run
concurrently leading to unsynchronized access to params.

This permits races for both the failure and success paths after
ctrl_thread_status is stored.
  * params->ret may be loaded in ctrl_thread_init failure path
  * params->arg may be loaded in ctrl_thread_start or
    control_thread_start when calling start_routine.

For ctrl_thread_init remove the params->ret load and just return 1 since
it is only interpreted as a indicator of success / failure of
ctrl_thread_init.

For {ctrl,control}_thread_start store param->arg in stack allocated
storage prior to calling ctrl_thread_init and use the copy when calling
start_routine.

For control_thread_start if ctrl_thread_init fails just return 0 instead
of loading params->ret, since the value returned is unused when
ctrl_thread_status is set to CTRL_THREAD_ERROR when ctrl_thread_init
fails.

Fixes: 878b7468eacb ("eal: add platform agnostic control thread API")

Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
---
 lib/eal/common/eal_common_thread.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/eal/common/eal_common_thread.c b/lib/eal/common/eal_common_thread.c
index edb9d4e..079a385 100644
--- a/lib/eal/common/eal_common_thread.c
+++ b/lib/eal/common/eal_common_thread.c
@@ -256,7 +256,7 @@ static int ctrl_thread_init(void *arg)
 	if (params->ret != 0) {
 		__atomic_store_n(&params->ctrl_thread_status,
 			CTRL_THREAD_ERROR, __ATOMIC_RELEASE);
-		return params->ret;
+		return 1;
 	}
 
 	__atomic_store_n(&params->ctrl_thread_status,
@@ -268,23 +268,25 @@ static int ctrl_thread_init(void *arg)
 static void *ctrl_thread_start(void *arg)
 {
 	struct rte_thread_ctrl_params *params = arg;
+	void *start_arg = params->arg;
 	void *(*start_routine)(void *) = params->u.ctrl_start_routine;
 
 	if (ctrl_thread_init(arg) != 0)
 		return NULL;
 
-	return start_routine(params->arg);
+	return start_routine(start_arg);
 }
 
 static uint32_t control_thread_start(void *arg)
 {
 	struct rte_thread_ctrl_params *params = arg;
+	void *start_arg = params->arg;
 	rte_thread_func start_routine = params->u.control_start_routine;
 
 	if (ctrl_thread_init(arg) != 0)
-		return params->ret;
+		return 0;
 
-	return start_routine(params->arg);
+	return start_routine(start_arg);
 }
 
 int
-- 
1.8.3.1