netdev - [PATCH net-next] net: wwan: mhi_wwan_ctrl: Fix RX buffer starvation

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Date:   Tue, 20 Apr 2021 11:36:22 +0200
From:   Loic Poulain <loic.poulain@...aro.org>
To:     kuba@...nel.org, davem@...emloft.net
Cc:     netdev@...r.kernel.org, Loic Poulain <loic.poulain@...aro.org>
Subject: [PATCH net-next] net: wwan: mhi_wwan_ctrl: Fix RX buffer starvation

The mhi_wwan_rx_budget_dec function is supposed to return true if
RX buffer budget has been successfully decremented, allowing to queue
a new RX buffer for transfer. However the current implementation is
broken when RX budget is '1', in which case budget is decremented but
false is returned, preventing to requeue one buffer, and leading to
RX buffer starvation.

Fixes: fa588eba632d ("net: Add Qcom WWAN control driver")
Signed-off-by: Loic Poulain <loic.poulain@...aro.org>
---
 drivers/net/wwan/mhi_wwan_ctrl.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wwan/mhi_wwan_ctrl.c b/drivers/net/wwan/mhi_wwan_ctrl.c
index 11475ad..1fc2376 100644
--- a/drivers/net/wwan/mhi_wwan_ctrl.c
+++ b/drivers/net/wwan/mhi_wwan_ctrl.c
@@ -56,11 +56,11 @@ static bool mhi_wwan_rx_budget_dec(struct mhi_wwan_dev *mhiwwan)
 
 	spin_lock(&mhiwwan->rx_lock);
 
-	if (mhiwwan->rx_budget)
+	if (mhiwwan->rx_budget) {
 		mhiwwan->rx_budget--;
-
-	if (mhiwwan->rx_budget && test_bit(MHI_WWAN_RX_REFILL, &mhiwwan->flags))
-		ret = true;
+		if (test_bit(MHI_WWAN_RX_REFILL, &mhiwwan->flags))
+			ret = true;
+	}
 
 	spin_unlock(&mhiwwan->rx_lock);
 
-- 
2.7.4