[PATCH 1/1] xen/netfront: stop tx queues during live migration

The tx queues are not stopped during the live migration. As a result, the
ndo_start_xmit() may access netfront_info->queues which is freed by
talk_to_netback()->xennet_destroy_queues().

This patch is to netif_device_detach() at the beginning of xen-netfront
resuming, and netif_device_attach() at the end of resuming.

     CPU A                                CPU B

 talk_to_netback()
 -> if (info->queues)
        xennet_destroy_queues(info);
    to free netfront_info->queues

                                        xennet_start_xmit()
                                        to access netfront_info->queues

  -> err = xennet_create_queues(info, &num_queues);

The idea is borrowed from virtio-net.

Cc: Joe Jin <redacted>
Signed-off-by: Dongli Zhang <redacted>
---
Since I am not able to reproduce the corner case on purpose, I create a
patch to reproduce.
https://raw.githubusercontent.com/finallyjustice/patchset/master/xen-netfront-send-GARP-during-live-migration.patch

 drivers/net/xen-netfront.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index e31b98403f31..fc41ba95f81d 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c

@@ -1730,6 +1730,10 @@ static int netfront_resume(struct xenbus_device *dev)
 
 	dev_dbg(&dev->dev, "%s\n", dev->nodename);
 
+	netif_tx_lock_bh(info->netdev);
+	netif_device_detach(info->netdev);
+	netif_tx_unlock_bh(info->netdev);
+
 	xennet_disconnect_backend(info);
 	return 0;
 }

@@ -2349,6 +2353,10 @@ static int xennet_connect(struct net_device *dev)
 	 * domain a kick because we've probably just requeued some
 	 * packets.
 	 */
+	netif_tx_lock_bh(np->netdev);
+	netif_device_attach(np->netdev);
+	netif_tx_unlock_bh(np->netdev);
+
 	netif_carrier_on(np->netdev);
 	for (j = 0; j < num_queues; ++j) {
 		queue = &np->queues[j];

-- 
2.17.1

Hello:

This patch was applied to netdev/net.git (master)
by David S. Miller [off-list ref]:

On Fri, 22 Oct 2021 16:31:39 -0700 you wrote:

The tx queues are not stopped during the live migration. As a result, the
ndo_start_xmit() may access netfront_info->queues which is freed by
talk_to_netback()->xennet_destroy_queues().

This patch is to netif_device_detach() at the beginning of xen-netfront
resuming, and netif_device_attach() at the end of resuming.

[...]

Here is the summary with links:
  - [1/1] xen/netfront: stop tx queues during live migration
    https://git.kernel.org/netdev/net/c/042b2046d0f0

You are awesome, thank you!
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