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Re: [Qemu-devel] [PATCH] qom: In function object_set_link_property(), fi


From: Alexander Barabash
Subject: Re: [Qemu-devel] [PATCH] qom: In function object_set_link_property(), first call object_ref(), then object_unref().
Date: Wed, 22 Feb 2012 19:19:33 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.2) Gecko/20120216 Thunderbird/10.0.2

On 02/22/2012 07:17 PM, Paolo Bonzini wrote:
On 02/22/2012 06:13 PM, address@hidden wrote:
From: Alexander Barabash<address@hidden>

In the old implementation, if the new value of the property links
to the same object, as the old value, that object is first unref-ed,
and then ref-ed. This leads to unintended deinitialization of that object.

In the new implementation, this is fixed.

Signed-off-by: Alexander Barabash<address@hidden>
---
  qom/object.c |   18 +++++++++++++-----
  1 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/qom/object.c b/qom/object.c
index 941c291..d1b3ac7 100644
--- a/qom/object.c
+++ b/qom/object.c
@@ -892,19 +892,19 @@ static void object_set_link_property(Object *obj, Visitor 
*v, void *opaque,
                                       const char *name, Error **errp)
  {
      Object **child = opaque;
+    Object *old_target;
      bool ambiguous = false;
      const char *type;
      char *path;
      gchar *target_type;
+    bool clear_old_target = true;

      type = object_property_get_type(obj, name, NULL);

      visit_type_str(v,&path, name, errp);

-    if (*child) {
-        object_unref(*child);
-        *child = NULL;
-    }
+    old_target = *child;
+    *child = NULL;
You can just remove the unref here...

      if (strcmp(path, "") != 0) {
          Object *target;
@@ -916,7 +916,11 @@ static void object_set_link_property(Object *obj, Visitor 
*v, void *opaque,
          if (ambiguous) {
              error_set(errp, QERR_AMBIGUOUS_PATH, path);
          } else if (target) {
-            object_ref(target);
+            if (target != old_target) {
+                object_ref(target);
... leave the unconditional ref to target here...

+            } else {
+                clear_old_target = false;
+            }
              *child = target;
          } else {
              target = object_resolve_path(path,&ambiguous);
@@ -930,6 +934,10 @@ static void object_set_link_property(Object *obj, Visitor 
*v, void *opaque,
      }

      g_free(path);
+
+    if (clear_old_target&&  (old_target != NULL)) {
+        object_unref(old_target);
... and leave this unref on old_target, without the need for
clear_old_target.

+    }
  }

  void object_property_add_link(Object *obj, const char *name,
Paolo
Agreed.
Alex




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