[dpdk-dev] [PATCH 1/2] raw/ioat: fix ring space checks

[Bruce Richardson <bruce.richardson@intel.com>]

When enqueuing a descriptor, when checking that there is at least one
slot free for the current descriptor and a later batch descriptor, we
need to test for both two free and one free, in case the last write
was a batch descriptor which is allowed to use the "spare" slot.

Similarly, when computing the free space in the ring to return to the
user, we need to take account of the same condition, so that we do not
return a "-1" ring space value, by blindly subtracting "2".

Fixes: 245efe544d8e ("raw/ioat: report status of completed jobs")

Reported-by: Jiayu Hu <jiayu.hu@intel.com>
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
---
 drivers/raw/ioat/rte_idxd_rawdev_fns.h | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/raw/ioat/rte_idxd_rawdev_fns.h b/drivers/raw/ioat/rte_idxd_rawdev_fns.h
index 862e0eb41..6ed67d77e 100644
--- a/drivers/raw/ioat/rte_idxd_rawdev_fns.h
+++ b/drivers/raw/ioat/rte_idxd_rawdev_fns.h
@@ -132,7 +132,7 @@ __idxd_burst_capacity(int dev_id)
 	struct rte_idxd_rawdev *idxd =
 			(struct rte_idxd_rawdev *)rte_rawdevs[dev_id].dev_private;
 	uint16_t write_idx = idxd->batch_start + idxd->batch_size;
-	uint16_t used_space;
+	uint16_t used_space, free_space;
 
 	/* Check for space in the batch ring */
 	if ((idxd->batch_idx_read == 0 && idxd->batch_idx_write == idxd->max_batches) ||
@@ -147,7 +147,10 @@ __idxd_burst_capacity(int dev_id)
 	/* Return amount of free space in the descriptor ring
 	 * subtract 1 for space for batch descriptor and 1 for possible null desc
 	 */
-	return idxd->desc_ring_mask - used_space - 2;
+	free_space = idxd->desc_ring_mask - used_space;
+	if (free_space < 2)
+		return 0;
+	return free_space - 2;
 }
 
 static __rte_always_inline rte_iova_t
@@ -174,7 +177,8 @@ __idxd_write_desc(int dev_id,
 			idxd->batch_idx_write + 1 == idxd->batch_idx_read)
 		goto failed;
 	/* for descriptor ring, we always need a slot for batch completion */
-	if (((write_idx + 2) & mask) == idxd->hdls_read)
+	if (((write_idx + 2) & mask) == idxd->hdls_read ||
+			((write_idx + 1) & mask) == idxd->hdls_read)
 		goto failed;
 
 	/* write desc and handle. Note, descriptors don't wrap */
-- 
2.30.2