linux-kernel - [PATCH 4.14 74/91] net: ena: fix napi handler misbehavior when the napi budget is zero

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Date:   Thu,  2 Jan 2020 23:07:56 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Netanel Belgazal <netanel@...zon.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.14 74/91] net: ena: fix napi handler misbehavior when the napi budget is zero

From: Netanel Belgazal <netanel@...zon.com>

[ Upstream commit 24dee0c7478d1a1e00abdf5625b7f921467325dc ]

In netpoll the napi handler could be called with budget equal to zero.
Current ENA napi handler doesn't take that into consideration.

The napi handler handles Rx packets in a do-while loop.
Currently, the budget check happens only after decrementing the
budget, therefore the napi handler, in rare cases, could run over
MAX_INT packets.

In addition to that, this moves all budget related variables to int
calculation and stop mixing u32 to avoid ambiguity

Fixes: 1738cd3ed342 ("net: ena: Add a driver for Amazon Elastic Network Adapters (ENA)")
Signed-off-by: Netanel Belgazal <netanel@...zon.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/ethernet/amazon/ena/ena_netdev.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
+++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
@@ -1196,8 +1196,8 @@ static int ena_io_poll(struct napi_struc
 	struct ena_napi *ena_napi = container_of(napi, struct ena_napi, napi);
 	struct ena_ring *tx_ring, *rx_ring;
 
-	u32 tx_work_done;
-	u32 rx_work_done;
+	int tx_work_done;
+	int rx_work_done = 0;
 	int tx_budget;
 	int napi_comp_call = 0;
 	int ret;
@@ -1214,7 +1214,11 @@ static int ena_io_poll(struct napi_struc
 	}
 
 	tx_work_done = ena_clean_tx_irq(tx_ring, tx_budget);
-	rx_work_done = ena_clean_rx_irq(rx_ring, napi, budget);
+	/* On netpoll the budget is zero and the handler should only clean the
+	 * tx completions.
+	 */
+	if (likely(budget))
+		rx_work_done = ena_clean_rx_irq(rx_ring, napi, budget);
 
 	/* If the device is about to reset or down, avoid unmask
 	 * the interrupt and return 0 so NAPI won't reschedule