linux-kernel - [PATCH 4.9 21/96] xen-netback: dont populate the hash cache on XenBus disconnect

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Message-Id: <20190312171036.123110394@linuxfoundation.org>
Date:   Tue, 12 Mar 2019 10:09:39 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Igor Druzhinin <igor.druzhinin@...rix.com>,
        Paul Durrant <paul.durrant@...rix.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 4.9 21/96] xen-netback: dont populate the hash cache on XenBus disconnect

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Igor Druzhinin <igor.druzhinin@...rix.com>

[ Upstream commit a2288d4e355992d369c50c45d017a85f6061ff71 ]

Occasionally, during the disconnection procedure on XenBus which
includes hash cache deinitialization there might be some packets
still in-flight on other processors. Handling of these packets includes
hashing and hash cache population that finally results in hash cache
data structure corruption.

In order to avoid this we prevent hashing of those packets if there
are no queues initialized. In that case RCU protection of queues guards
the hash cache as well.

Signed-off-by: Igor Druzhinin <igor.druzhinin@...rix.com>
Reviewed-by: Paul Durrant <paul.durrant@...rix.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/net/xen-netback/hash.c      |    2 ++
 drivers/net/xen-netback/interface.c |    7 +++++++
 2 files changed, 9 insertions(+)

--- a/drivers/net/xen-netback/hash.c
+++ b/drivers/net/xen-netback/hash.c
@@ -435,6 +435,8 @@ void xenvif_init_hash(struct xenvif *vif
 	if (xenvif_hash_cache_size == 0)
 		return;
 
+	BUG_ON(vif->hash.cache.count);
+
 	spin_lock_init(&vif->hash.cache.lock);
 	INIT_LIST_HEAD(&vif->hash.cache.list);
 }
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -152,6 +152,13 @@ static u16 xenvif_select_queue(struct ne
 {
 	struct xenvif *vif = netdev_priv(dev);
 	unsigned int size = vif->hash.size;
+	unsigned int num_queues;
+
+	/* If queues are not set up internally - always return 0
+	 * as the packet going to be dropped anyway */
+	num_queues = READ_ONCE(vif->num_queues);
+	if (num_queues < 1)
+		return 0;
 
 	if (vif->hash.alg == XEN_NETIF_CTRL_HASH_ALGORITHM_NONE)
 		return fallback(dev, skb) % dev->real_num_tx_queues;