[dpdk-dev] [PATCH v2] eal: fix race in ctrl thread creation

[Olivier Matz]

As reported by Luc, there is a race where the barrier is destroyed by
one thread, while the other thread did not yet leave
pthread_barrier_wait.

This patch fixes the race condition by adding an atomic counter to
ensure that the barrier is destroyed only it is not used by any thread.

Fixes: 3a0d465d4c53 ("eal: fix use-after-free on control thread creation")
Cc: jianfeng....@intel.com
Cc: sta...@dpdk.org

Reported-by: Luc Pelletier <lucp.at.w...@gmail.com>
Signed-off-by: David Marchand <david.march...@redhat.com>
Signed-off-by: Olivier Matz <olivier.m...@6wind.com>
---

Hi Luc,

Thank you for reporting this problem and submitting the patch.
I think the issue can be fixed without any loop, like in this
patch. What do you think?

Regards,
Olivier


 lib/librte_eal/common/eal_common_thread.c | 38 +++++++++++++----------
 1 file changed, 21 insertions(+), 17 deletions(-)

diff --git a/lib/librte_eal/common/eal_common_thread.c 
b/lib/librte_eal/common/eal_common_thread.c
index 73a055902a..891f825e87 100644
--- a/lib/librte_eal/common/eal_common_thread.c
+++ b/lib/librte_eal/common/eal_common_thread.c
@@ -170,11 +170,11 @@ struct rte_thread_ctrl_params {
        void *(*start_routine)(void *);
        void *arg;
        pthread_barrier_t configured;
+       unsigned int barrier_refcnt;
 };
 
 static void *ctrl_thread_init(void *arg)
 {
-       int ret;
        struct internal_config *internal_conf =
                eal_get_internal_configuration();
        rte_cpuset_t *cpuset = &internal_conf->ctrl_cpuset;
@@ -184,8 +184,9 @@ static void *ctrl_thread_init(void *arg)
 
        __rte_thread_init(rte_lcore_id(), cpuset);
 
-       ret = pthread_barrier_wait(&params->configured);
-       if (ret == PTHREAD_BARRIER_SERIAL_THREAD) {
+       pthread_barrier_wait(&params->configured);
+       if (__atomic_sub_fetch(&params->barrier_refcnt, 1,
+                               __ATOMIC_ACQ_REL) == 0) {
                pthread_barrier_destroy(&params->configured);
                free(params);
        }
@@ -210,15 +211,17 @@ rte_ctrl_thread_create(pthread_t *thread, const char 
*name,
 
        params->start_routine = start_routine;
        params->arg = arg;
-
-       pthread_barrier_init(&params->configured, NULL, 2);
-
-       ret = pthread_create(thread, attr, ctrl_thread_init, (void *)params);
+       __atomic_store_n(&params->barrier_refcnt, 2, __ATOMIC_RELEASE);
+       ret = pthread_barrier_init(&params->configured, NULL, 2);
        if (ret != 0) {
                free(params);
                return -ret;
        }
 
+       ret = pthread_create(thread, attr, ctrl_thread_init, (void *)params);
+       if (ret != 0)
+               goto fail;
+
        if (name != NULL) {
                ret = rte_thread_setname(*thread, name);
                if (ret < 0)
@@ -227,25 +230,26 @@ rte_ctrl_thread_create(pthread_t *thread, const char 
*name,
        }
 
        ret = pthread_setaffinity_np(*thread, sizeof(*cpuset), cpuset);
-       if (ret)
-               goto fail;
+       if (ret != 0)
+               goto fail_cancel;
 
-       ret = pthread_barrier_wait(&params->configured);
-       if (ret == PTHREAD_BARRIER_SERIAL_THREAD) {
+       pthread_barrier_wait(&params->configured);
+       if (__atomic_sub_fetch(&params->barrier_refcnt, 1,
+                               __ATOMIC_ACQ_REL) == 0) {
                pthread_barrier_destroy(&params->configured);
                free(params);
        }
 
        return 0;
 
-fail:
-       if (PTHREAD_BARRIER_SERIAL_THREAD ==
-           pthread_barrier_wait(&params->configured)) {
-               pthread_barrier_destroy(&params->configured);
-               free(params);
-       }
+fail_cancel:
        pthread_cancel(*thread);
        pthread_join(*thread, NULL);
+
+fail:
+       pthread_barrier_destroy(&params->configured);
+       free(params);
+
        return -ret;
 }
 
-- 
2.29.2