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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, Igor Druzhinin <igor.druzhinin@citrix.com>,
        Juergen Gross <jgross@suse.com>, Wei Liu <wl@xen.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 32/60] xen/netback: avoid race in xenvif_rx_ring_slots_available()
Date:   Mon, 15 Feb 2021 16:27:20 +0100
Message-Id: <20210215152716.382419020@linuxfoundation.org>
In-Reply-To: <20210215152715.401453874@linuxfoundation.org>
References: <20210215152715.401453874@linuxfoundation.org>
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From: Juergen Gross <jgross@suse.com>

[ Upstream commit ec7d8e7dd3a59528e305a18e93f1cb98f7faf83b ]

Since commit 23025393dbeb3b8b3 ("xen/netback: use lateeoi irq binding")
xenvif_rx_ring_slots_available() is no longer called only from the rx
queue kernel thread, so it needs to access the rx queue with the
associated queue held.

Reported-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Fixes: 23025393dbeb3b8b3 ("xen/netback: use lateeoi irq binding")
Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wl@xen.org>
Link: https://lore.kernel.org/r/20210202070938.7863-1-jgross@suse.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/xen-netback/rx.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/xen-netback/rx.c b/drivers/net/xen-netback/rx.c
index 9b62f65b630e4..48e2006f96ce6 100644
--- a/drivers/net/xen-netback/rx.c
+++ b/drivers/net/xen-netback/rx.c
@@ -38,10 +38,15 @@ static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue)
 	RING_IDX prod, cons;
 	struct sk_buff *skb;
 	int needed;
+	unsigned long flags;
+
+	spin_lock_irqsave(&queue->rx_queue.lock, flags);
 
 	skb = skb_peek(&queue->rx_queue);
-	if (!skb)
+	if (!skb) {
+		spin_unlock_irqrestore(&queue->rx_queue.lock, flags);
 		return false;
+	}
 
 	needed = DIV_ROUND_UP(skb->len, XEN_PAGE_SIZE);
 	if (skb_is_gso(skb))
@@ -49,6 +54,8 @@ static bool xenvif_rx_ring_slots_available(struct xenvif_queue *queue)
 	if (skb->sw_hash)
 		needed++;
 
+	spin_unlock_irqrestore(&queue->rx_queue.lock, flags);
+
 	do {
 		prod = queue->rx.sring->req_prod;
 		cons = queue->rx.req_cons;
-- 
2.27.0