[qemu-xen stable-4.13] xen-bus: Fix backend state transition on device reset

[patchbot@xxxxxxx]

commit b6cedc911e44a5bc6f3f120fee411c1ccc22f220
Author:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
AuthorDate: Fri Aug 23 11:15:33 2019 +0100
Commit:     Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
CommitDate: Sun Oct 27 23:42:16 2019 -0500

    xen-bus: Fix backend state transition on device reset
    
    When a frontend wants to reset its state and the backend one, it
    starts with setting "Closing", then waits for the backend (QEMU) to do
    the same.
    
    But when QEMU is setting "Closing" to its state, it triggers an event
    (xenstore watch) that re-execute xen_device_backend_changed() and set
    the backend state to "Closed". QEMU should wait for the frontend to
    set "Closed" before doing the same.
    
    Before setting "Closed" to the backend_state, we are also going to
    check if there is a frontend. If that the case, when the backend state
    is set to "Closing" the frontend should react and sets its state to
    "Closing" then "Closed". The backend should wait for that to happen.
    
    Fixes: b6af8926fb858c4f1426e5acb2cfc1f0580ec98a
    Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    Message-Id: <20190823101534.465-2-anthony.perard@xxxxxxxxxx>
    (cherry picked from commit cb3231460747552d70af9d546dc53d8195bcb796)
    Signed-off-by: Michael Roth <mdroth@xxxxxxxxxxxxxxxxxx>
---
 hw/xen/xen-bus.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 7503eea9e9..5929aa4b2e 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -516,6 +516,23 @@ static void xen_device_backend_set_online(XenDevice 
*xendev, bool online)
     xen_device_backend_printf(xendev, "online", "%u", online);
 }
 
+/*
+ * Tell from the state whether the frontend is likely alive,
+ * i.e. it will react to a change of state of the backend.
+ */
+static bool xen_device_state_is_active(enum xenbus_state state)
+{
+    switch (state) {
+    case XenbusStateInitWait:
+    case XenbusStateInitialised:
+    case XenbusStateConnected:
+    case XenbusStateClosing:
+        return true;
+    default:
+        return false;
+    }
+}
+
 static void xen_device_backend_changed(void *opaque)
 {
     XenDevice *xendev = opaque;
@@ -539,11 +556,11 @@ static void xen_device_backend_changed(void *opaque)
 
     /*
      * If the toolstack (or unplug request callback) has set the backend
-     * state to Closing, but there is no active frontend (i.e. the
-     * state is not Connected) then set the backend state to Closed.
+     * state to Closing, but there is no active frontend then set the
+     * backend state to Closed.
      */
     if (xendev->backend_state == XenbusStateClosing &&
-        xendev->frontend_state != XenbusStateConnected) {
+        !xen_device_state_is_active(state)) {
         xen_device_backend_set_state(xendev, XenbusStateClosed);
     }
 
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.13