[libvirt] [libvirt-glib 5/5] mainloop: don't reschedule deleted timeouts/watches

[Christophe Fergeau]

The deletion of libvirt timeouts/watches is done in 2 steps:
- the first step is synchronous and unregisters the timeout/watch
  from glib mainloop
- the second step is asynchronous and triggered from the first step.
  It releases the memory used for bookkeeping for the timeout/watch
  being deleted

This is done this way to avoid some possible deadlocks when
reentering the sync callback while freeing the memory associated
with the timeout/watch.

However, it's possible to call gvir_event_update_handle after
gvir_event_remove_handle but before _event_handle_remove does
the final cleanup. When this happen, _update_handle will reregister
the handle with glib mainloop, and bad things will happen when
a glib callback is triggered for this event after _event_handle_remove
has freed the memory associated with this handle watch.

This commit marks the timeouts and watches as removed in the
synchronous _remove callback and makes sure removed timeouts/watches
are ignored in _update callbacks.
---
 libvirt-glib/libvirt-glib-event.c |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/libvirt-glib/libvirt-glib-event.c b/libvirt-glib/libvirt-glib-event.c
index 587a59e..657c1bf 100644
--- a/libvirt-glib/libvirt-glib-event.c
+++ b/libvirt-glib/libvirt-glib-event.c
@@ -87,7 +87,7 @@ struct gvir_event_handle
     int watch;
     int fd;
     int events;
-    int enabled;
+    int removed;
     GIOChannel *channel;
     guint source;
     virEventHandleCallback cb;
@@ -99,6 +99,7 @@ struct gvir_event_timeout
 {
     int timer;
     int interval;
+    int removed;
     guint source;
     virEventTimeoutCallback cb;
     void *opaque;
@@ -195,7 +196,7 @@ gvir_event_handle_find(int watch)
             continue;
         }
 
-        if (h->watch == watch) {
+        if ((h->watch == watch) && !h->removed) {
             return h;
         }
     }
@@ -289,6 +290,11 @@ gvir_event_handle_remove(int watch)
     g_source_remove(data->source);
     data->source = 0;
     data->events = 0;
+    /* since the actual watch deletion is done asynchronously, a handle_update call may
+     * reschedule the watch before it's fully deleted, that's why we need to mark it as
+     * 'removed' to prevent reuse
+     */
+    data->removed = TRUE;
     g_idle_add(_event_handle_remove, data);
 
     ret = 0;
@@ -358,7 +364,7 @@ gvir_event_timeout_find(int timer)
             continue;
         }
 
-        if (t->timer == timer) {
+        if ((t->timer == timer) && !t->removed) {
             return t;
         }
     }
@@ -441,6 +447,11 @@ gvir_event_timeout_remove(int timer)
 
     g_source_remove(data->source);
     data->source = 0;
+    /* since the actual timeout deletion is done asynchronously, a timeout_update call may
+     * reschedule the timeout before it's fully deleted, that's why we need to mark it as
+     * 'removed' to prevent reuse
+     */
+    data->removed = TRUE;
     g_idle_add(_event_timeout_remove, data);
 
     ret = 0;
-- 
1.7.10.2