[net-next v3 4/5] net: tc35815: rework network interface interrupt logic

[Christian Marangi]

Rework network interface logic. Before this change, the code flow was:
1. Disable interrupt
2. Try to schedule a NAPI
3. Check if it was possible (NAPI is not already scheduled)
4. emit BUG() if we receive interrupt while a NAPI is scheduled

If some application busy poll or set gro_flush_timeout low enough, it's
possible to reach the BUG() condition. Given that the condition may
happen and it wouldn't be a bug, rework the logic to permit such case
and prevent stall with interrupt never enabled again.

Disable the interrupt only if the NAPI can be scheduled (aka it's not
already scheduled) and drop the printk and BUG() call. With these
change, in the event of a NAPI already scheduled, the interrupt is
simply ignored with nothing done.

Suggested-by: Eric Dumazet <edumazet at google.com>
Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>
---
 drivers/net/ethernet/toshiba/tc35815.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/toshiba/tc35815.c b/drivers/net/ethernet/toshiba/tc35815.c
index 14cf6ecf6d0d..6e3758dfbdbd 100644
--- a/drivers/net/ethernet/toshiba/tc35815.c
+++ b/drivers/net/ethernet/toshiba/tc35815.c
@@ -1434,14 +1434,10 @@ static irqreturn_t tc35815_interrupt(int irq, void *dev_id)
 	u32 dmactl = tc_readl(&tr->DMA_Ctl);
 
 	if (!(dmactl & DMA_IntMask)) {
-		/* disable interrupts */
-		tc_writel(dmactl | DMA_IntMask, &tr->DMA_Ctl);
-		if (napi_schedule_prep(&lp->napi))
+		if (napi_schedule_prep(&lp->napi)) {
+			/* disable interrupts */
+			tc_writel(dmactl | DMA_IntMask, &tr->DMA_Ctl);
 			__napi_schedule(&lp->napi);
-		else {
-			printk(KERN_ERR "%s: interrupt taken in poll\n",
-			       dev->name);
-			BUG();
 		}
 		(void)tc_readl(&tr->Int_Src);	/* flush */
 		return IRQ_HANDLED;
-- 
2.40.1