eal: fix race condition in IPC request

Unlocking the action list before sending message and locking it
again afterwards introduces a window where a response might
arrive before we have a chance to start waiting on a condition,
resulting in timeouts on valid messages.

Fixes: 783b6e54971d ("eal: add synchronous multi-process communication")
Cc: stable@dpdk.org
Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Jianfeng Tan <jianfeng.tan@intel.com>

diff --git a/lib/librte_eal/common/eal_common_proc.c b/lib/librte_eal/common/eal_common_proc.c
index 3a1088e..da7930f 100644 (file)
--- a/lib/librte_eal/common/eal_common_proc.c
+++ b/lib/librte_eal/common/eal_common_proc.c
@@ -561,10 +561,10 @@ mp_request_one(const char *dst, struct rte_mp_msg *req,
        exist = find_sync_request(dst, req->name);
        if (!exist)
                TAILQ_INSERT_TAIL(&sync_requests.requests, &sync_req, next);
-       pthread_mutex_unlock(&sync_requests.lock);
        if (exist) {
                RTE_LOG(ERR, EAL, "A pending request %s:%s\n", dst, req->name);
                rte_errno = EEXIST;
+               pthread_mutex_unlock(&sync_requests.lock);
                return -1;
        }
 
@@ -578,7 +578,6 @@ mp_request_one(const char *dst, struct rte_mp_msg *req,
 
        reply->nb_sent++;
 
-       pthread_mutex_lock(&sync_requests.lock);
        do {
                pthread_cond_timedwait(&sync_req.cond, &sync_requests.lock, ts);
                /* Check spurious wakeups */