Changeset 107229 in vbox

Timestamp:

Dec 4, 2024 9:01:51 PM (8 weeks ago)

Author:

vboxsync

Message:

Main/Medium: Address broken reference counting of medium back references
when snapshots are involved. Follow-up to r165743 to handle the
scenario of running a restored snapshot with attached removable media
since in this case there won't be a call to Medium::i_removeBackReference()
for the removable media associated with the machine since the snapshot
is running and as such the reference count remains at '1' for the
removable media device(s) even after all the back references in the
snapshots are removed.

File:

• trunk/src/VBox/Main/src-server/MediumImpl.cpp (modified) (1 diff)

trunk/src/VBox/Main/src-server/MediumImpl.cpp

@@ -4819 +4819 @@
     }
 
-    /* if the backref becomes empty, remove it */
-    if (it->fInCurState == false && it->iRefCnt == 0 && it->llSnapshotIds.size() == 0)
+    /* The common case is that the backref will become "empty" with the reference
+     * count dropping to zero (iRefCnt=0), fInCurState=false, and no more snapshot
+     * references (llSnapshotIds.size()=0) and thus the back reference is removed
+     * at that point.  However there is an exception and that is when a restored
+     * snapshot is running and in that case there will be no i_removeBackReference()
+     * call for any attached removable device referencing just the machine
+     * (aSnapshotId.isZero()) so in such cases iRefCnt will be '1' and won't ever
+     * drop to zero so remove such back references here as well. */
+    if (   it->fInCurState == false
+        && it->llSnapshotIds.size() == 0
+        && (it->iRefCnt == 0 || (fDvd && it->iRefCnt == 1)))
         m->backRefs.erase(it);