Btrfs: use a bit to track if we're in the radix tree

For creating a dummy in-memory btree I need to be able to use the radix tree to
keep track of the buffers like normal extent buffers.  With dummy buffers we
skip the radix tree step, and we still want to do that for the tree mod log
dummy buffers but for my test buffers we need to be able to remove them from the
radix tree like normal.  This will give me a way to do that.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/extent_io.c

@@ -4617,6 +4617,7 @@ again:
 	}
 	/* add one reference for the tree */
 	check_buffer_tree_ref(eb);
+	set_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags);
 
 	/*
 	 * there is a race where release page may have
@@ -4660,9 +4661,7 @@ static int release_extent_buffer(struct extent_buffer *eb)
 {
 	WARN_ON(atomic_read(&eb->refs) == 0);
 	if (atomic_dec_and_test(&eb->refs)) {
-		if (test_bit(EXTENT_BUFFER_DUMMY, &eb->bflags)) {
-			spin_unlock(&eb->refs_lock);
-		} else {
+		if (test_and_clear_bit(EXTENT_BUFFER_IN_TREE, &eb->bflags)) {
 			struct extent_io_tree *tree = eb->tree;
 
 			spin_unlock(&eb->refs_lock);
@@ -4671,6 +4670,8 @@ static int release_extent_buffer(struct extent_buffer *eb)
 			radix_tree_delete(&tree->buffer,
 					  eb->start >> PAGE_CACHE_SHIFT);
 			spin_unlock(&tree->buffer_lock);
+		} else {
+			spin_unlock(&eb->refs_lock);
 		}
 
 		/* Should be safe to release our pages at this point */

fs/btrfs/extent_io.h

@@ -43,6 +43,7 @@
 #define EXTENT_BUFFER_WRITEBACK 7
 #define EXTENT_BUFFER_IOERR 8
 #define EXTENT_BUFFER_DUMMY 9
+#define EXTENT_BUFFER_IN_TREE 10
 
 /* these are flags for extent_clear_unlock_delalloc */
 #define PAGE_UNLOCK		(1 << 0)