[PATCH] Cache->Cursor may point to Slab

[Owen Smith <owen.smith@xxxxxxxxx>]

Its possible that the Cursor refers to the only Slab that has no
allocated objects, but there are other slabs which are fully
allocated. The current ASSERTions are not valid, and needs rework.

Also adds more comments and ASSERTions to validate whats going on.

Signed-off-by: Owen Smith <owen.smith@xxxxxxxxx>
---
 src/xenbus/cache.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/xenbus/cache.c b/src/xenbus/cache.c
index 6229aed..821f66a 100644
--- a/src/xenbus/cache.c
+++ b/src/xenbus/cache.c
@@ -479,20 +479,25 @@ CacheDestroySlab(
 
     //
     // The only reason the cursor should be pointing at this slab is
-    // if it is the only one in the list.
+    // if it is the only one in the list with no allocated objects.
     //
     if (Cache->Cursor == &Slab->ListEntry) {
         ASSERT3P(Slab->ListEntry.Flink, ==, &Cache->SlabList);
-        ASSERT3P(Slab->ListEntry.Blink, ==, &Cache->SlabList);
+        // Slab->ListEntry.Blink could refer to a fully allocated Slab
+        // Set Cursor to SlabList, so next CacheGet allocates a new Slab
         Cache->Cursor = &Cache->SlabList;
     }
 
     RemoveEntryList(&Slab->ListEntry);
+    // If Cache->Cursor == &Cache->SlabList,
+    //     either; all entries in SlabList are fully allocated; or
+    //             SlabList is empty
+    // If Cache->Cursor != &Cache->SlabList,
+    //     Cache->Cursor is the first Slab that is not fully allocated
 
-    ASSERT(IMPLY(Cache->Cursor == &Cache->SlabList,
-                 IsListEmpty(&Cache->SlabList)));
+    CacheAudit(Cache);
 
-    Index = CacheMaskSize(Slab->Allocated);
+    Index = CacheMaskSize(Slab->Constructed);
     while (--Index >= 0) {
         PVOID Object = (PVOID)&Slab->Buffer[Index * Cache->Size];
 
@@ -501,6 +506,7 @@ CacheDestroySlab(
             __CacheMaskClear(Slab->Constructed, Index);
         }
     }
+    ASSERT3U(CacheMaskCount(Slab->Constructed), ==, 0);
 
     ASSERT(Cache->CurrentSlabs != 0);
     InterlockedDecrement(&Cache->CurrentSlabs);
-- 
2.44.0.windows.1