Windows: ObjectInfo RefCount 0 <-> 1 transitions

When the reference count transitions from 0 <-> 1 ensure that the
ObjectInfoLock is held exclusive to prevent the current thread from
altering the state while another thread is holding the ObjectInfoLock
shared in order to conditionally perform an action based upon
the the reference count being zero.

Change-Id: I5bcf384a0ea90e4896e55b537e92112ac3791a4c
Reviewed-on: http://gerrit.openafs.org/8257
Reviewed-by: Rod Widdowson <rdw@steadingsoftware.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>

diff --git a/src/WINNT/afsrdr/kernel/lib/AFSGeneric.cpp b/src/WINNT/afsrdr/kernel/lib/AFSGeneric.cpp
index fc85688c0cde880b054ba111b5431e644291fd10..6a7a9388df36979c93f2049c335b8f7d5a4e5f69 100644 (file)
--- a/src/WINNT/afsrdr/kernel/lib/AFSGeneric.cpp
+++ b/src/WINNT/afsrdr/kernel/lib/AFSGeneric.cpp
@@ -6543,10 +6543,31 @@ AFSObjectInfoIncrement( IN AFSObjectInfoCB *ObjectInfo)
 
     LONG lCount;
 
-    AFSAcquireShared( &ObjectInfo->NonPagedInfo->ObjectInfoLock,
-                      TRUE);
+    if ( ObjectInfo->ObjectReferenceCount == 0)
+    {
+
+        AFSAcquireExcl( &ObjectInfo->NonPagedInfo->ObjectInfoLock,
+                        TRUE);
+
+        lCount = InterlockedIncrement( &ObjectInfo->ObjectReferenceCount);
+    }
+    else
+    {
+
+        AFSAcquireShared( &ObjectInfo->NonPagedInfo->ObjectInfoLock,
+                          TRUE);
+
+        lCount = InterlockedIncrement( &ObjectInfo->ObjectReferenceCount);
+
+        if ( lCount == 1)
+        {
 
-    lCount = InterlockedIncrement( &ObjectInfo->ObjectReferenceCount);
+            AFSReleaseResource( &ObjectInfo->NonPagedInfo->ObjectInfoLock);
+
+            AFSAcquireExcl( &ObjectInfo->NonPagedInfo->ObjectInfoLock,
+                            TRUE);
+        }
+    }
 
     AFSReleaseResource( &ObjectInfo->NonPagedInfo->ObjectInfoLock);
 
@@ -6564,6 +6585,19 @@ AFSObjectInfoDecrement( IN AFSObjectInfoCB *ObjectInfo)
 
     lCount = InterlockedDecrement( &ObjectInfo->ObjectReferenceCount);
 
+    if ( lCount == 0)
+    {
+
+        lCount = InterlockedIncrement( &ObjectInfo->ObjectReferenceCount);
+
+        AFSReleaseResource(&ObjectInfo->NonPagedInfo->ObjectInfoLock);
+
+        AFSAcquireExcl( &ObjectInfo->NonPagedInfo->ObjectInfoLock,
+                        TRUE);
+
+        lCount = InterlockedDecrement( &ObjectInfo->ObjectReferenceCount);
+    }
+
     AFSReleaseResource( &ObjectInfo->NonPagedInfo->ObjectInfoLock);
 
     return lCount;