Patch "Revert "xen-netback: Check for hotplug-status existence before watching"" has been added to the 4.9-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    Revert "xen-netback: Check for hotplug-status existence before watching"

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     revert-xen-netback-check-for-hotplug-status-existenc.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit f1ec4184db02f0b93c70e4c11a3b3c549c81eac9
Author: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
Date:   Tue Feb 22 01:18:17 2022 +0100

    Revert "xen-netback: Check for hotplug-status existence before watching"
    
    [ Upstream commit e8240addd0a3919e0fd7436416afe9aa6429c484 ]
    
    This reverts commit 2afeec08ab5c86ae21952151f726bfe184f6b23d.
    
    The reasoning in the commit was wrong - the code expected to setup the
    watch even if 'hotplug-status' didn't exist. In fact, it relied on the
    watch being fired the first time - to check if maybe 'hotplug-status' is
    already set to 'connected'. Not registering a watch for non-existing
    path (which is the case if hotplug script hasn't been executed yet),
    made the backend not waiting for the hotplug script to execute. This in
    turns, made the netfront think the interface is fully operational, while
    in fact it was not (the vif interface on xen-netback side might not be
    configured yet).
    
    This was a workaround for 'hotplug-status' erroneously being removed.
    But since that is reverted now, the workaround is not necessary either.
    
    More discussion at
    https://lore.kernel.org/xen-devel/afedd7cb-a291-e773-8b0d-4db9b291fa98@xxxxxxxx/T/#u
    
    Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
    Reviewed-by: Michael Brown <mbrown@xxxxxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20220222001817.2264967-2-marmarek@xxxxxxxxxxxxxxxxxxxxxx
    Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index e6646c8a7bdb..78788402edd8 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -1040,15 +1040,11 @@ static void connect(struct backend_info *be)
 	xenvif_carrier_on(be->vif);
 
 	unregister_hotplug_status_watch(be);
-	if (xenbus_exists(XBT_NIL, dev->nodename, "hotplug-status")) {
-		err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch,
-					   NULL, hotplug_status_changed,
-					   "%s/%s", dev->nodename,
-					   "hotplug-status");
-		if (err)
-			goto err;
+	err = xenbus_watch_pathfmt(dev, &be->hotplug_status_watch, NULL,
+				   hotplug_status_changed,
+				   "%s/%s", dev->nodename, "hotplug-status");
+	if (!err)
 		be->have_hotplug_status_watch = 1;
-	}
 
 	netif_tx_wake_all_queues(be->vif->dev);