Fix hang on netfront removal

Fixes QubesOS/qubes-issues#3657

patches.xen/c2d2e6738a20-xen-netfront-Fix-hang-on-device-removal.patch

@@ -0,0 +1,53 @@
+From c2d2e6738a209f0f9dffa2dc8e7292fc45360d61 Mon Sep 17 00:00:00 2001
+From: Jason Andryuk <jandryuk@gmail.com>
+Date: Wed, 28 Feb 2018 07:23:23 -0500
+Subject: [PATCH] xen-netfront: Fix hang on device removal
+
+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@gmail.com>
+Cc: Eduardo Otubo <otubo@redhat.com>
+Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
+Signed-off-by: Juergen Gross <jgross@suse.com>
+---
+ 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,
+-- 
+2.17.0
+

series.conf

@@ -30,6 +30,9 @@ patches.xen/2a22ee6c3ab1-xen-xenbus_dev_frontend-Fix-XS_TRANSACTION_END-handl.pa
 patches.xen/b93008d1ac65-xen-xenbus-Catch-closing-of-non-existent-transaction.patch
 patches.xen/8fe5ab411209-xen-xenbus_dev_frontend-Verify-body-of-XS_TRANSACTIO.patch
 
+# Fix for hang on netfront removal
+patches.xen/c2d2e6738a20-xen-netfront-Fix-hang-on-device-removal.patch
+
 # Hardware-specific fixes, backported from newer kernel and/or developers branches
 patches.backports/v2-2-2-Input-synaptics---Lenovo-X1-Carbon-5-should-use-SMBUS-RMI.patch
 patches.backports/Input-synaptics---add-Intertouch-support-on-X1-Carbon-6th-and-X280.patch