linux-kernel - [PATCH] xen-netfront: Fix hang on device removal

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Message-Id: <20180228122323.3914-1-jandryuk@gmail.com>
Date:   Wed, 28 Feb 2018 07:23:23 -0500
From:   Jason Andryuk <jandryuk@...il.com>
To:     xen-devel@...ts.xenproject.org, netdev@...r.kernel.org
Cc:     Jason Andryuk <jandryuk@...il.com>,
        Eduardo Otubo <otubo@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        linux-kernel@...r.kernel.org (open list)
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@...il.com>
Cc: Eduardo Otubo <otubo@...hat.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,
-- 
2.14.3