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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, Catherine Sullivan <csully@google.com>,
        David Awogbemila <awogbemila@google.com>,
        Willem de Brujin <willemb@google.com>,
        "David S. Miller" <davem@davemloft.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 155/177] gve: Upgrade memory barrier in poll routine
Date:   Mon, 31 May 2021 15:15:12 +0200
Message-Id: <20210531130653.278430907@linuxfoundation.org>
In-Reply-To: <20210531130647.887605866@linuxfoundation.org>
References: <20210531130647.887605866@linuxfoundation.org>
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From: Catherine Sullivan <csully@google.com>

[ Upstream commit f81781835f0adfae8d701545386030d223efcd6f ]

As currently written, if the driver checks for more work (via
gve_tx_poll or gve_rx_poll) before the device posts work and the
irq doorbell is not unmasked
(via iowrite32be(GVE_IRQ_ACK | GVE_IRQ_EVENT, ...)) before the device
attempts to raise an interrupt, an interrupt is lost and this could
potentially lead to the traffic being completely halted. For
example, if a tx queue has already been stopped, the driver won't get
the chance to complete work and egress will be halted.

We need a full memory barrier in the poll
routine to ensure that the irq doorbell is unmasked before the driver
checks for more work.

Fixes: f5cedc84a30d ("gve: Add transmit and receive support")
Signed-off-by: Catherine Sullivan <csully@google.com>
Signed-off-by: David Awogbemila <awogbemila@google.com>
Acked-by: Willem de Brujin <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/ethernet/google/gve/gve_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index 77e79d2939ba..6ea0975d74a1 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -121,7 +121,7 @@ static int gve_napi_poll(struct napi_struct *napi, int budget)
 	/* Double check we have no extra work.
 	 * Ensure unmask synchronizes with checking for work.
 	 */
-	dma_rmb();
+	mb();
 	if (block->tx)
 		reschedule |= gve_tx_poll(block, -1);
 	if (block->rx)
-- 
2.30.2