mcslock: fix hang in weak memory model

[dpdk.git] / lib / librte_eal / include / generic / rte_mcslock.h

diff --git a/lib/librte_eal/include/generic/rte_mcslock.h b/lib/librte_eal/include/generic/rte_mcslock.h
index 78b0df2..d370bef 100644 (file)
--- a/lib/librte_eal/include/generic/rte_mcslock.h
+++ b/lib/librte_eal/include/generic/rte_mcslock.h
@@ -64,7 +64,14 @@ rte_mcslock_lock(rte_mcslock_t **msl, rte_mcslock_t *me)
                 */
                return;
        }
-       __atomic_store_n(&prev->next, me, __ATOMIC_RELAXED);
+       /* The store to me->next above should also complete before the node is
+        * visible to predecessor thread releasing the lock. Hence, the store
+        * prev->next also requires release semantics. Note that, for example,
+        * on ARM, the release semantics in the exchange operation is not
+        * strong as a release fence and is not sufficient to enforce the
+        * desired order here.
+        */
+       __atomic_store_n(&prev->next, me, __ATOMIC_RELEASE);
 
        /* The while-load of me->locked should not move above the previous
         * store to prev->next. Otherwise it will cause a deadlock. Need a