[PATCH AUTOSEL 5.4 069/187] net: ena: fix napi handler misbehavior when the napi budget is zero

Sasha Levin
2019-12-27T17:55:19Z

From: Netanel Belgazal <netanel@amazon.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@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/ethernet/amazon/ena/ena_netdev.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c
index c487d2a7d6dd..b4a145220aba 100644
--- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
+++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
@@ -1238,8 +1238,8 @@ static int ena_io_poll(struct napi_struct *napi, int budget)
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;
@@ -1256,7 +1256,11 @@ static int ena_io_poll(struct napi_struct *napi, int budget)
}

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
--
2.20.1