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

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

[Christian Marangi]

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@vger.kernel.org
Signed-off-by: Christian Marangi <ansuelsmth@gmail.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

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

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Mon,  2 Oct 2023 16:08:05 +0200 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [net] net: ethernet: mediatek: disable irq before schedule napi
    https://git.kernel.org/netdev/net/c/fcdfc462881d

You are awesome, thank you!
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