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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Joao Pinto <jpinto@synopsys.com>,
        "David S. Miller" <davem@davemloft.net>,
        Giuseppe Cavallaro <peppe.cavallaro@st.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        Jose Abreu <joabreu@synopsys.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.20 075/183] net: stmmac: Prevent RX starvation in stmmac_napi_poll()
Date:   Mon, 25 Feb 2019 22:10:48 +0100
Message-Id: <20190225195107.102335094@linuxfoundation.org>
In-Reply-To: <20190225195054.748060397@linuxfoundation.org>
References: <20190225195054.748060397@linuxfoundation.org>
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4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit fa0be0a43f101888ac677dba31b590963eafeaa1 ]

Currently, TX is given a budget which is consumed by stmmac_tx_clean()
and stmmac_rx() is given the remaining non-consumed budget.

This is wrong and in case we are sending a large number of packets this
can starve RX because remaining budget will be low.

Let's give always the same budget for RX and TX clean.

While at it, check if we missed any interrupts while we were in NAPI
callback by looking at DMA interrupt status.

Cc: Joao Pinto <jpinto@synopsys.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 .../net/ethernet/stmicro/stmmac/stmmac_main.c | 27 ++++++++++---------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index fe9240e15aeac..5d83d6a7694b0 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -3525,27 +3525,28 @@ static int stmmac_napi_poll(struct napi_struct *napi, int budget)
 	struct stmmac_channel *ch =
 		container_of(napi, struct stmmac_channel, napi);
 	struct stmmac_priv *priv = ch->priv_data;
-	int work_done = 0, work_rem = budget;
+	int work_done, rx_done = 0, tx_done = 0;
 	u32 chan = ch->index;
 
 	priv->xstats.napi_poll++;
 
-	if (ch->has_tx) {
-		int done = stmmac_tx_clean(priv, work_rem, chan);
+	if (ch->has_tx)
+		tx_done = stmmac_tx_clean(priv, budget, chan);
+	if (ch->has_rx)
+		rx_done = stmmac_rx(priv, budget, chan);
 
-		work_done += done;
-		work_rem -= done;
-	}
-
-	if (ch->has_rx) {
-		int done = stmmac_rx(priv, work_rem, chan);
+	work_done = max(rx_done, tx_done);
+	work_done = min(work_done, budget);
 
-		work_done += done;
-		work_rem -= done;
-	}
+	if (work_done < budget && napi_complete_done(napi, work_done)) {
+		int stat;
 
-	if (work_done < budget && napi_complete_done(napi, work_done))
 		stmmac_enable_dma_irq(priv, priv->ioaddr, chan);
+		stat = stmmac_dma_interrupt_status(priv, priv->ioaddr,
+						   &priv->xstats, chan);
+		if (stat && napi_reschedule(napi))
+			stmmac_disable_dma_irq(priv, priv->ioaddr, chan);
+	}
 
 	return work_done;
 }
-- 
2.19.1