netdev - [net PATCH] net: ethernet: mediatek: disable irq before schedule napi

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Message-Id: <20231002140805.568-1-ansuelsmth@gmail.com>
Date: Mon,  2 Oct 2023 16:08:05 +0200
From: Christian Marangi <ansuelsmth@...il.com>
To: Felix Fietkau <nbd@....name>,
	John Crispin <john@...ozen.org>,
	Sean Wang <sean.wang@...iatek.com>,
	Mark Lee <Mark-MC.Lee@...iatek.com>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Michael Lee <igvtee@...il.com>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org
Cc: Christian Marangi <ansuelsmth@...il.com>,
	stable@...r.kernel.org
Subject: [net PATCH] net: ethernet: mediatek: disable irq before schedule napi

While searching for possible refactor of napi_schedule_prep and
__napi_schedule it was notice that the mtk eth driver disable the
interrupt for rx and tx AFTER napi is scheduled.

While this is a very hard to repro case it might happen to have
situation where the interrupt is disabled and never enabled again as the
napi completes and the interrupt is enabled before.

This is caused by the fact that a napi driven by interrupt expect a
logic with:
1. interrupt received. napi prepared -> interrupt disabled -> napi
   scheduled
2. napi triggered. ring cleared -> interrupt enabled -> wait for new
   interrupt

To prevent this case, disable the interrupt BEFORE the napi is
scheduled.

Fixes: 656e705243fd ("net-next: mediatek: add support for MT7623 ethernet")
Cc: stable@...r.kernel.org
Signed-off-by: Christian Marangi <ansuelsmth@...il.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 82b51072aad8..7669b446915a 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -3172,8 +3172,8 @@ static irqreturn_t mtk_handle_irq_rx(int irq, void *_eth)
 
 	eth->rx_events++;
 	if (likely(napi_schedule_prep(&eth->rx_napi))) {
-		__napi_schedule(&eth->rx_napi);
 		mtk_rx_irq_disable(eth, eth->soc->txrx.rx_irq_done_mask);
+		__napi_schedule(&eth->rx_napi);
 	}
 
 	return IRQ_HANDLED;
@@ -3185,8 +3185,8 @@ static irqreturn_t mtk_handle_irq_tx(int irq, void *_eth)
 
 	eth->tx_events++;
 	if (likely(napi_schedule_prep(&eth->tx_napi))) {
-		__napi_schedule(&eth->tx_napi);
 		mtk_tx_irq_disable(eth, MTK_TX_DONE_INT);
+		__napi_schedule(&eth->tx_napi);
 	}
 
 	return IRQ_HANDLED;
-- 
2.40.1