[dpdk-dev] [PATCH v2 2/3] kni: fix kni fifo synchronization

[Phil Yang <phil.yang@arm.com>]

With existing code in kni_fifo_put, rx_q values are not being updated
before updating fifo_write. While reading rx_q in kni_net_rx_normal,
This is causing the sync issue on other core. The same situation happens
in kni_fifo_get as well.

So syncing the values by adding C11 atomic memory barriers to make sure
the values being synced before updating fifo_write and fifo_read.

Fixes: 3fc5ca2 ("kni: initial import")
Signed-off-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
Reviewed-by: Gavin Hu <Gavin.Hu@arm.com>
---
 .../linuxapp/eal/include/exec-env/rte_kni_common.h |  5 ++++
 lib/librte_kni/rte_kni_fifo.h                      | 30 +++++++++++++++++++++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
index cfa9448..1fd713b 100644
--- a/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
+++ b/lib/librte_eal/linuxapp/eal/include/exec-env/rte_kni_common.h
@@ -54,8 +54,13 @@ struct rte_kni_request {
  * Writing should never overwrite the read position
  */
 struct rte_kni_fifo {
+#ifndef RTE_USE_C11_MEM_MODEL
 	volatile unsigned write;     /**< Next position to be written*/
 	volatile unsigned read;      /**< Next position to be read */
+#else
+	unsigned write;              /**< Next position to be written*/
+	unsigned read;               /**< Next position to be read */
+#endif
 	unsigned len;                /**< Circular buffer length */
 	unsigned elem_size;          /**< Pointer size - for 32/64 bit OS */
 	void *volatile buffer[];     /**< The buffer contains mbuf pointers */
diff --git a/lib/librte_kni/rte_kni_fifo.h b/lib/librte_kni/rte_kni_fifo.h
index ac26a8c..f4171a1 100644
--- a/lib/librte_kni/rte_kni_fifo.h
+++ b/lib/librte_kni/rte_kni_fifo.h
@@ -28,8 +28,13 @@ kni_fifo_put(struct rte_kni_fifo *fifo, void **data, unsigned num)
 {
 	unsigned i = 0;
 	unsigned fifo_write = fifo->write;
-	unsigned fifo_read = fifo->read;
 	unsigned new_write = fifo_write;
+#ifdef RTE_USE_C11_MEM_MODEL
+	unsigned fifo_read = __atomic_load_n(&fifo->read,
+						 __ATOMIC_ACQUIRE);
+#else
+	unsigned fifo_read = fifo->read;
+#endif
 
 	for (i = 0; i < num; i++) {
 		new_write = (new_write + 1) & (fifo->len - 1);
@@ -39,7 +44,12 @@ kni_fifo_put(struct rte_kni_fifo *fifo, void **data, unsigned num)
 		fifo->buffer[fifo_write] = data[i];
 		fifo_write = new_write;
 	}
+#ifdef RTE_USE_C11_MEM_MODEL
+	__atomic_store_n(&fifo->write, fifo_write, __ATOMIC_RELEASE);
+#else
+	rte_smp_wmb();
 	fifo->write = fifo_write;
+#endif
 	return i;
 }
 
@@ -51,7 +61,12 @@ kni_fifo_get(struct rte_kni_fifo *fifo, void **data, unsigned num)
 {
 	unsigned i = 0;
 	unsigned new_read = fifo->read;
+#ifdef RTE_USE_C11_MEM_MODEL
+	unsigned fifo_write = __atomic_load_n(&fifo->write, __ATOMIC_ACQUIRE);
+#else
 	unsigned fifo_write = fifo->write;
+#endif
+
 	for (i = 0; i < num; i++) {
 		if (new_read == fifo_write)
 			break;
@@ -59,7 +74,12 @@ kni_fifo_get(struct rte_kni_fifo *fifo, void **data, unsigned num)
 		data[i] = fifo->buffer[new_read];
 		new_read = (new_read + 1) & (fifo->len - 1);
 	}
+#ifdef RTE_USE_C11_MEM_MODEL
+	__atomic_store_n(&fifo->read, new_read, __ATOMIC_RELEASE);
+#else
+	rte_smp_wmb();
 	fifo->read = new_read;
+#endif
 	return i;
 }
 
@@ -69,5 +89,13 @@ kni_fifo_get(struct rte_kni_fifo *fifo, void **data, unsigned num)
 static inline uint32_t
 kni_fifo_count(struct rte_kni_fifo *fifo)
 {
+#ifdef RTE_USE_C11_MEM_MODEL
+	unsigned fifo_write = __atomic_load_n(&fifo->write,
+						  __ATOMIC_ACQUIRE);
+	unsigned fifo_read = __atomic_load_n(&fifo->read,
+						 __ATOMIC_ACQUIRE);
+	return (fifo->len + fifo_write - fifo_read) & (fifo->len - 1);
+#else
 	return (fifo->len + fifo->write - fifo->read) & (fifo->len - 1);
+#endif
 }
-- 
2.7.4