linux-kernel - [PATCH v2] net: macb: Increment rx bd head after allocating skb and buffer

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Date:   Thu, 12 May 2022 22:49:00 +0530
From:   Harini Katakam <harini.katakam@...inx.com>
To:     <nicolas.ferre@...rochip.com>, <davem@...emloft.net>,
        <claudiu.beznea@...rochip.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <michal.simek@...inx.com>, <harinikatakamlinux@...il.com>,
        <harini.katakam@...inx.com>, <radhey.shyam.pandey@...inx.com>
Subject: [PATCH v2] net: macb: Increment rx bd head after allocating skb and buffer

In gem_rx_refill rx_prepared_head is incremented at the beginning of
the while loop preparing the skb and data buffers. If the skb or data
buffer allocation fails, this BD will be unusable BDs until the head
loops back to the same BD (and obviously buffer allocation succeeds).
In the unlikely event that there's a string of allocation failures,
there will be an equal number of unusable BDs and an inconsistent RX
BD chain. Hence increment the head at the end of the while loop to be
clean.

Fixes: 4df95131ea80 ("net/macb: change RX path for GEM")
Signed-off-by: Harini Katakam <harini.katakam@...inx.com>
Signed-off-by: Michal Simek <michal.simek@...inx.com>
Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
---
v2:
Add Fixes tag and Reviewed-by tag

 drivers/net/ethernet/cadence/macb_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 0b03305ad6a0..9c7d590c0188 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -1215,7 +1215,6 @@ static void gem_rx_refill(struct macb_queue *queue)
 		/* Make hw descriptor updates visible to CPU */
 		rmb();
 
-		queue->rx_prepared_head++;
 		desc = macb_rx_desc(queue, entry);
 
 		if (!queue->rx_skbuff[entry]) {
@@ -1254,6 +1253,7 @@ static void gem_rx_refill(struct macb_queue *queue)
 			dma_wmb();
 			desc->addr &= ~MACB_BIT(RX_USED);
 		}
+		queue->rx_prepared_head++;
 	}
 
 	/* Make descriptor updates visible to hardware */
-- 
2.17.1