[Xen-devel] [PATCH] xen-netfront: Fix hang on device removal

[Jason Andryuk <jandryuk@xxxxxxxxx>]

A toolstack may delete the vif frontend and backend xenstore entries
while xen-netfront is in the removal code path.  In that case, the
checks for xenbus_read_driver_state would return XenbusStateUnknown, and
xennet_remove would hang indefinitely.  This hang prevents system
shutdown.

xennet_remove must be able to handle XenbusStateUnknown, and
netback_changed must also wake up the wake_queue for that state as well.

Fixes: 5b5971df3bc2 ("xen-netfront: remove warning when unloading module")

Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
Cc: Eduardo Otubo <otubo@xxxxxxxxxx>
---
 drivers/net/xen-netfront.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 8328d395e332..3127bc8633ca 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -2005,7 +2005,10 @@ static void netback_changed(struct xenbus_device *dev,
        case XenbusStateInitialised:
        case XenbusStateReconfiguring:
        case XenbusStateReconfigured:
+               break;
+
        case XenbusStateUnknown:
+               wake_up_all(&module_unload_q);
                break;
 
        case XenbusStateInitWait:
@@ -2136,7 +2139,9 @@ static int xennet_remove(struct xenbus_device *dev)
                xenbus_switch_state(dev, XenbusStateClosing);
                wait_event(module_unload_q,
                           xenbus_read_driver_state(dev->otherend) ==
-                          XenbusStateClosing);
+                          XenbusStateClosing ||
+                          xenbus_read_driver_state(dev->otherend) ==
+                          XenbusStateUnknown);
 
                xenbus_switch_state(dev, XenbusStateClosed);
                wait_event(module_unload_q,
-- 
2.14.3


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