ethdev: fix memory ordering for callback functions

Call back functions are registered on the control plane. They
are accessed from the data plane. Hence, correct memory orderings
should be used to avoid race conditions.

Fixes: 4dc294158cac ("ethdev: support optional Rx and Tx callbacks")
Fixes: c8231c63ddcb ("ethdev: insert Rx callback as head of list")
Cc: stable@dpdk.org
Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
index 2198548..7eaeccc 100644 (file)
--- a/lib/librte_ethdev/rte_ethdev.c
+++ b/lib/librte_ethdev/rte_ethdev.c
@@ -4610,12 +4610,20 @@ rte_eth_add_rx_callback(uint16_t port_id, uint16_t queue_id,
                rte_eth_devices[port_id].post_rx_burst_cbs[queue_id];
 
        if (!tail) {
-               rte_eth_devices[port_id].post_rx_burst_cbs[queue_id] = cb;
+               /* Stores to cb->fn and cb->param should complete before
+                * cb is visible to data plane.
+                */
+               __atomic_store_n(
+                       &rte_eth_devices[port_id].post_rx_burst_cbs[queue_id],
+                       cb, __ATOMIC_RELEASE);
 
        } else {
                while (tail->next)
                        tail = tail->next;
-               tail->next = cb;
+               /* Stores to cb->fn and cb->param should complete before
+                * cb is visible to data plane.
+                */
+               __atomic_store_n(&tail->next, cb, __ATOMIC_RELEASE);
        }
        rte_spinlock_unlock(&rte_eth_rx_cb_lock);
 
@@ -4700,12 +4708,20 @@ rte_eth_add_tx_callback(uint16_t port_id, uint16_t queue_id,
                rte_eth_devices[port_id].pre_tx_burst_cbs[queue_id];
 
        if (!tail) {
-               rte_eth_devices[port_id].pre_tx_burst_cbs[queue_id] = cb;
+               /* Stores to cb->fn and cb->param should complete before
+                * cb is visible to data plane.
+                */
+               __atomic_store_n(
+                       &rte_eth_devices[port_id].pre_tx_burst_cbs[queue_id],
+                       cb, __ATOMIC_RELEASE);
 
        } else {
                while (tail->next)
                        tail = tail->next;
-               tail->next = cb;
+               /* Stores to cb->fn and cb->param should complete before
+                * cb is visible to data plane.
+                */
+               __atomic_store_n(&tail->next, cb, __ATOMIC_RELEASE);
        }
        rte_spinlock_unlock(&rte_eth_tx_cb_lock);
 
@@ -4736,7 +4752,7 @@ rte_eth_remove_rx_callback(uint16_t port_id, uint16_t queue_id,
                cb = *prev_cb;
                if (cb == user_cb) {
                        /* Remove the user cb from the callback list. */
-                       *prev_cb = cb->next;
+                       __atomic_store_n(prev_cb, cb->next, __ATOMIC_RELAXED);
                        ret = 0;
                        break;
                }
@@ -4770,7 +4786,7 @@ rte_eth_remove_tx_callback(uint16_t port_id, uint16_t queue_id,
                cb = *prev_cb;
                if (cb == user_cb) {
                        /* Remove the user cb from the callback list. */
-                       *prev_cb = cb->next;
+                       __atomic_store_n(prev_cb, cb->next, __ATOMIC_RELAXED);
                        ret = 0;
                        break;
                }

diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
index f07dbc4..c37b3a1 100644 (file)
--- a/lib/librte_ethdev/rte_ethdev.h
+++ b/lib/librte_ethdev/rte_ethdev.h
@@ -3911,7 +3911,8 @@ struct rte_eth_rxtx_callback;
  *   The callback function
  * @param user_param
  *   A generic pointer parameter which will be passed to each invocation of the
- *   callback function on this port and queue.
+ *   callback function on this port and queue. Inter-thread synchronization
+ *   of any user data changes is the responsibility of the user.
  *
  * @return
  *   NULL on error.
@@ -3940,7 +3941,8 @@ rte_eth_add_rx_callback(uint16_t port_id, uint16_t queue_id,
  *   The callback function
  * @param user_param
  *   A generic pointer parameter which will be passed to each invocation of the
- *   callback function on this port and queue.
+ *   callback function on this port and queue. Inter-thread synchronization
+ *   of any user data changes is the responsibility of the user.
  *
  * @return
  *   NULL on error.
@@ -3968,7 +3970,8 @@ rte_eth_add_first_rx_callback(uint16_t port_id, uint16_t queue_id,
  *   The callback function
  * @param user_param
  *   A generic pointer parameter which will be passed to each invocation of the
- *   callback function on this port and queue.
+ *   callback function on this port and queue. Inter-thread synchronization
+ *   of any user data changes is the responsibility of the user.
  *
  * @return
  *   NULL on error.
@@ -3993,7 +3996,9 @@ rte_eth_add_tx_callback(uint16_t port_id, uint16_t queue_id,
  *   on that queue.
  *
  * - After a short delay - where the delay is sufficient to allow any
- *   in-flight callbacks to complete.
+ *   in-flight callbacks to complete. Alternately, the RCU mechanism can be
+ *   used to detect when data plane threads have ceased referencing the
+ *   callback memory.
  *
  * @param port_id
  *   The port identifier of the Ethernet device.
@@ -4026,7 +4031,9 @@ int rte_eth_remove_rx_callback(uint16_t port_id, uint16_t queue_id,
  *   on that queue.
  *
  * - After a short delay - where the delay is sufficient to allow any
- *   in-flight callbacks to complete.
+ *   in-flight callbacks to complete. Alternately, the RCU mechanism can be
+ *   used to detect when data plane threads have ceased referencing the
+ *   callback memory.
  *
  * @param port_id
  *   The port identifier of the Ethernet device.
@@ -4687,10 +4694,18 @@ rte_eth_rx_burst(uint16_t port_id, uint16_t queue_id,
                                     rx_pkts, nb_pkts);
 
 #ifdef RTE_ETHDEV_RXTX_CALLBACKS
-       if (unlikely(dev->post_rx_burst_cbs[queue_id] != NULL)) {
-               struct rte_eth_rxtx_callback *cb =
-                               dev->post_rx_burst_cbs[queue_id];
+       struct rte_eth_rxtx_callback *cb;
 
+       /* __ATOMIC_RELEASE memory order was used when the
+        * call back was inserted into the list.
+        * Since there is a clear dependency between loading
+        * cb and cb->fn/cb->next, __ATOMIC_ACQUIRE memory order is
+        * not required.
+        */
+       cb = __atomic_load_n(&dev->post_rx_burst_cbs[queue_id],
+                               __ATOMIC_RELAXED);
+
+       if (unlikely(cb != NULL)) {
                do {
                        nb_rx = cb->fn.rx(port_id, queue_id, rx_pkts, nb_rx,
                                                nb_pkts, cb->param);
@@ -4953,7 +4968,16 @@ rte_eth_tx_burst(uint16_t port_id, uint16_t queue_id,
 #endif
 
 #ifdef RTE_ETHDEV_RXTX_CALLBACKS
-       struct rte_eth_rxtx_callback *cb = dev->pre_tx_burst_cbs[queue_id];
+       struct rte_eth_rxtx_callback *cb;
+
+       /* __ATOMIC_RELEASE memory order was used when the
+        * call back was inserted into the list.
+        * Since there is a clear dependency between loading
+        * cb and cb->fn/cb->next, __ATOMIC_ACQUIRE memory order is
+        * not required.
+        */
+       cb = __atomic_load_n(&dev->pre_tx_burst_cbs[queue_id],
+                               __ATOMIC_RELAXED);
 
        if (unlikely(cb != NULL)) {
                do {