[PATCH net] net: lantiq: disable interrupt before sheduling NAPI

This patch fixes TX hangs with threaded NAPI enabled. The scheduled
NAPI seems to be executed in parallel with the interrupt on second
thread. Sometimes it happens that ltq_dma_disable_irq() is executed
after xrx200_tx_housekeeping(). The symptom is that TX interrupts
are disabled in the DMA controller. As a result, the TX hangs after
a few seconds of the iperf test. Scheduling NAPI after disabling
interrupts fixes this issue.

Tested on Lantiq xRX200 (BT Home Hub 5A).

Fixes: 9423361da523 ("net: lantiq: Disable IRQs only if NAPI gets scheduled ")
Signed-off-by: Aleksander Jan Bajkowski <redacted>
---
 drivers/net/ethernet/lantiq_xrx200.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/lantiq_xrx200.c b/drivers/net/ethernet/lantiq_xrx200.c
index 36dc3e5f6218..0e10d8aeffe1 100644
--- a/drivers/net/ethernet/lantiq_xrx200.c
+++ b/drivers/net/ethernet/lantiq_xrx200.c

@@ -352,8 +352,8 @@ static irqreturn_t xrx200_dma_irq(int irq, void *ptr)
 	struct xrx200_chan *ch = ptr;
 
 	if (napi_schedule_prep(&ch->napi)) {
-		__napi_schedule(&ch->napi);
 		ltq_dma_disable_irq(&ch->dma);
+		__napi_schedule(&ch->napi);
 	}
 
 	ltq_dma_ack_irq(&ch->dma);

-- 
2.30.2

On 6/8/21 11:21 PM, Aleksander Jan Bajkowski wrote:

This patch fixes TX hangs with threaded NAPI enabled. The scheduled
NAPI seems to be executed in parallel with the interrupt on second
thread. Sometimes it happens that ltq_dma_disable_irq() is executed
after xrx200_tx_housekeeping(). The symptom is that TX interrupts
are disabled in the DMA controller. As a result, the TX hangs after
a few seconds of the iperf test. Scheduling NAPI after disabling
interrupts fixes this issue.

Tested on Lantiq xRX200 (BT Home Hub 5A).

Fixes: 9423361da523 ("net: lantiq: Disable IRQs only if NAPI gets scheduled ")
Signed-off-by: Aleksander Jan Bajkowski <redacted>

Acked-by: Hauke Mehrtens <hauke@hauke-m.de>

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Tue,  8 Jun 2021 23:21:07 +0200 you wrote:

This patch fixes TX hangs with threaded NAPI enabled. The scheduled
NAPI seems to be executed in parallel with the interrupt on second
thread. Sometimes it happens that ltq_dma_disable_irq() is executed
after xrx200_tx_housekeeping(). The symptom is that TX interrupts
are disabled in the DMA controller. As a result, the TX hangs after
a few seconds of the iperf test. Scheduling NAPI after disabling
interrupts fixes this issue.

[...]

Here is the summary with links:
  - [net] net: lantiq: disable interrupt before sheduling NAPI
    https://git.kernel.org/netdev/net/c/f2386cf7c5f4

You are awesome, thank you!
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