linux-kernel - [PATCH 5.12 254/296] gve: Upgrade memory barrier in poll routine

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Message-Id: <20210531130712.295650193@linuxfoundation.org>
Date:   Mon, 31 May 2021 15:15:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Catherine Sullivan <csully@...gle.com>,
        David Awogbemila <awogbemila@...gle.com>,
        Willem de Brujin <willemb@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.12 254/296] gve: Upgrade memory barrier in poll routine

From: Catherine Sullivan <csully@...gle.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@...gle.com>
Signed-off-by: David Awogbemila <awogbemila@...gle.com>
Acked-by: Willem de Brujin <willemb@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.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 21a5d058dab4..bbc423e93122 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -180,7 +180,7 @@ 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