9p/xen: fix init sequence

[ Upstream commit 7ef3ae82a6 ]

Large amount of mount hangs observed during hotplugging of 9pfs devices. The
9pfs Xen driver attempts to initialize itself more than once, causing the
frontend and backend to disagree: the backend listens on a channel that the
frontend does not send on, resulting in stalled processing.

Only allow initialization of 9p frontend once.

Fixes: c15fe55d14 ("9p/xen: fix connection sequence")
Signed-off-by: Alex Zenla <alex@edera.dev>
Signed-off-by: Alexander Merritt <alexander@edera.dev>
Signed-off-by: Ariadne Conill <ariadne@ariadne.space>
Reviewed-by: Juergen Gross <jgross@suse.com>
Message-ID: <20241119211633.38321-1-alexander@edera.dev>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

net/9p/trans_xen.c

@@ -466,6 +466,7 @@ static int xen_9pfs_front_init(struct xenbus_device *dev)
 		goto error;
 	}
 
+	xenbus_switch_state(dev, XenbusStateInitialised);
 	return 0;
 
  error_xenbus:
@@ -513,8 +514,10 @@ static void xen_9pfs_front_changed(struct xenbus_device *dev,
 		break;
 
 	case XenbusStateInitWait:
-		if (!xen_9pfs_front_init(dev))
-			xenbus_switch_state(dev, XenbusStateInitialised);
+		if (dev->state != XenbusStateInitialising)
+			break;
+
+		xen_9pfs_front_init(dev);
 		break;
 
 	case XenbusStateConnected: