Merge pull request #65 from versity/zab/item_cache_move_page_seq

Preserve item cache page max_seq as items move

ReleaseNotes.md

@@ -14,6 +14,15 @@ v1.x
   unmounted.   This can be used to change the mounts that will
   participate in quorum and the IP addresses they use.
 
+* **Fix Rare Risk of Item Cache Corruption**
+\
+  Code review found a rare potential source of item cache corruption.
+  If this happened it would look as though deleted parts of the filesystem
+  returned, but only at the time they were deleted.  Old deleted items are
+  not affected.  This problem only affected the item cache, never
+  persistent storage.  Unmounting and remounting would drop the bad item
+  cache and resync it with the correct persistent data.
+
 ---
 v1.0
 \

kmod/src/item.c

@@ -685,6 +685,12 @@ static void erase_page_items(struct cached_page *pg,
  * to the dirty list after the left page, and by adding items to the
  * tail of right's dirty list in key sort order.
  *
+ * The max_seq of the source page might be larger than all the items
+ * while protecting an erased item from being reclaimed while an older
+ * read is in flight.  We don't know where it might be in the source
+ * page so we have to assume that it's in the key range being moved and
+ * update the destination page's max_seq accordingly.
+ *
  * The caller is responsible for page locking and managing the lru.
  */
 static void move_page_items(struct super_block *sb,
@@ -726,6 +732,9 @@ static void move_page_items(struct super_block *sb,
 
 		erase_item(left, from);
 	}
+
+	if (left->max_seq > right->max_seq)
+		right->max_seq = left->max_seq;
 }
 
 enum page_intersection_type {