[PATCH 5.10 003/221] mt76: fix tx skb error handling in mt76_dma_tx_queue_skb

[Greg Kroah-Hartman]

From: Felix Fietkau <nbd@xxxxxxxx>

[ Upstream commit ae064fc0e32a4d28389086d9f4b260a0c157cfee ]

When running out of room in the tx queue after calling drv->tx_prepare_skb,
the buffer list will already have been modified on MT7615 and newer drivers.
This can leak a DMA mapping and will show up as swiotlb allocation failures
on x86.

Fix this by moving the queue length check further up. This is less accurate,
since it can overestimate the needed room in the queue on MT7615 and newer,
but the difference is small enough to not matter in practice.

Signed-off-by: Felix Fietkau <nbd@xxxxxxxx>
Signed-off-by: Kalle Valo <kvalo@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210216135119.23809-1-nbd@xxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/net/wireless/mediatek/mt76/dma.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/dma.c b/drivers/net/wireless/mediatek/mt76/dma.c
index 262c40dc14a6..665a03ebf9ef 100644
--- a/drivers/net/wireless/mediatek/mt76/dma.c
+++ b/drivers/net/wireless/mediatek/mt76/dma.c
@@ -355,7 +355,6 @@ mt76_dma_tx_queue_skb(struct mt76_dev *dev, enum mt76_txq_id qid,
 	};
 	struct ieee80211_hw *hw;
 	int len, n = 0, ret = -ENOMEM;
-	struct mt76_queue_entry e;
 	struct mt76_txwi_cache *t;
 	struct sk_buff *iter;
 	dma_addr_t addr;
@@ -397,6 +396,11 @@ mt76_dma_tx_queue_skb(struct mt76_dev *dev, enum mt76_txq_id qid,
 	}
 	tx_info.nbuf = n;
 
+	if (q->queued + (tx_info.nbuf + 1) / 2 >= q->ndesc - 1) {
+		ret = -ENOMEM;
+		goto unmap;
+	}
+
 	dma_sync_single_for_cpu(dev->dev, t->dma_addr, dev->drv->txwi_size,
 				DMA_TO_DEVICE);
 	ret = dev->drv->tx_prepare_skb(dev, txwi, qid, wcid, sta, &tx_info);
@@ -405,11 +409,6 @@ mt76_dma_tx_queue_skb(struct mt76_dev *dev, enum mt76_txq_id qid,
 	if (ret < 0)
 		goto unmap;
 
-	if (q->queued + (tx_info.nbuf + 1) / 2 >= q->ndesc - 1) {
-		ret = -ENOMEM;
-		goto unmap;
-	}
-
 	return mt76_dma_add_buf(dev, q, tx_info.buf, tx_info.nbuf,
 				tx_info.info, tx_info.skb, t);
 
@@ -425,9 +424,7 @@ mt76_dma_tx_queue_skb(struct mt76_dev *dev, enum mt76_txq_id qid,
 		dev->test.tx_done--;
 #endif
 
-	e.skb = tx_info.skb;
-	e.txwi = t;
-	dev->drv->tx_complete_skb(dev, &e);
+	dev_kfree_skb(tx_info.skb);
 	mt76_put_txwi(dev, t);
 	return ret;
 }
-- 
2.30.1