ring/c11: synchronize load and store of the tail

[dpdk.git] / lib / librte_ring / rte_ring_c11_mem.h

diff --git a/lib/librte_ring/rte_ring_c11_mem.h b/lib/librte_ring/rte_ring_c11_mem.h
index 94df3c4..52da95a 100644 (file)
--- a/lib/librte_ring/rte_ring_c11_mem.h
+++ b/lib/librte_ring/rte_ring_c11_mem.h
@@ -57,6 +57,7 @@ __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
                uint32_t *free_entries)
 {
        const uint32_t capacity = r->capacity;
+       uint32_t cons_tail;
        unsigned int max = n;
        int success;
 
@@ -67,13 +68,18 @@ __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
                *old_head = __atomic_load_n(&r->prod.head,
                                        __ATOMIC_ACQUIRE);
 
-               /*
-                *  The subtraction is done between two unsigned 32bits value
+               /* load-acquire synchronize with store-release of ht->tail
+                * in update_tail.
+                */
+               cons_tail = __atomic_load_n(&r->cons.tail,
+                                       __ATOMIC_ACQUIRE);
+
+               /* The subtraction is done between two unsigned 32bits value
                 * (the result is always modulo 32 bits even if we have
                 * *old_head > cons_tail). So 'free_entries' is always between 0
                 * and capacity (which is < size).
                 */
-               *free_entries = (capacity + r->cons.tail - *old_head);
+               *free_entries = (capacity + cons_tail - *old_head);
 
                /* check that we have enough room in ring */
                if (unlikely(n > *free_entries))
@@ -125,21 +131,29 @@ __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
                uint32_t *entries)
 {
        unsigned int max = n;
+       uint32_t prod_tail;
        int success;
 
        /* move cons.head atomically */
        do {
                /* Restore n as it may change every loop */
                n = max;
+
                *old_head = __atomic_load_n(&r->cons.head,
                                        __ATOMIC_ACQUIRE);
 
+               /* this load-acquire synchronize with store-release of ht->tail
+                * in update_tail.
+                */
+               prod_tail = __atomic_load_n(&r->prod.tail,
+                                       __ATOMIC_ACQUIRE);
+
                /* The subtraction is done between two unsigned 32bits value
                 * (the result is always modulo 32 bits even if we have
                 * cons_head > prod_tail). So 'entries' is always between 0
                 * and size(ring)-1.
                 */
-               *entries = (r->prod.tail - *old_head);
+               *entries = (prod_tail - *old_head);
 
                /* Set the actual entries for dequeue */
                if (n > *entries)