btrfs: add nesting tags to the locking helpers

We will need these when we switch to an rwsem, so plumb in the
infrastructure here to use later on.  I violate the 80 character limit
some here because it'll be cleaned up later.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.c

@@ -2875,7 +2875,8 @@ int btrfs_search_slot(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 			} else {
 				if (!btrfs_tree_read_lock_atomic(b)) {
 					btrfs_set_path_blocking(p);
-					__btrfs_tree_read_lock(b, p->recurse);
+					__btrfs_tree_read_lock(b, BTRFS_NESTING_NORMAL,
+							       p->recurse);
 				}
 				p->locks[level] = BTRFS_READ_LOCK;
 			}
@@ -5453,7 +5454,9 @@ int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
 			}
 			if (!ret) {
 				btrfs_set_path_blocking(path);
-				__btrfs_tree_read_lock(next, path->recurse);
+				__btrfs_tree_read_lock(next,
+						       BTRFS_NESTING_NORMAL,
+						       path->recurse);
 			}
 			next_rw_lock = BTRFS_READ_LOCK;
 		}
@@ -5488,7 +5491,9 @@ int btrfs_next_old_leaf(struct btrfs_root *root, struct btrfs_path *path,
 			ret = btrfs_try_tree_read_lock(next);
 			if (!ret) {
 				btrfs_set_path_blocking(path);
-				__btrfs_tree_read_lock(next, path->recurse);
+				__btrfs_tree_read_lock(next,
+						       BTRFS_NESTING_NORMAL,
+						       path->recurse);
 			}
 			next_rw_lock = BTRFS_READ_LOCK;
 		}

fs/btrfs/locking.c

@@ -244,7 +244,8 @@ void btrfs_set_lock_blocking_write(struct extent_buffer *eb)
  *
  * The rwlock is held upon exit.
  */
-void __btrfs_tree_read_lock(struct extent_buffer *eb, bool recurse)
+void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest,
+			    bool recurse)
 {
 	u64 start_ns = 0;
 
@@ -282,7 +283,7 @@ void __btrfs_tree_read_lock(struct extent_buffer *eb, bool recurse)
 
 void btrfs_tree_read_lock(struct extent_buffer *eb)
 {
-	__btrfs_tree_read_lock(eb, false);
+	__btrfs_tree_read_lock(eb, BTRFS_NESTING_NORMAL, false);
 }
 
 /*
@@ -415,7 +416,7 @@ void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
  *
  * The rwlock is held for write upon exit.
  */
-void btrfs_tree_lock(struct extent_buffer *eb)
+void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest)
 	__acquires(&eb->lock)
 {
 	u64 start_ns = 0;
@@ -440,6 +441,11 @@ void btrfs_tree_lock(struct extent_buffer *eb)
 	trace_btrfs_tree_lock(eb, start_ns);
 }
 
+void btrfs_tree_lock(struct extent_buffer *eb)
+{
+	__btrfs_tree_lock(eb, BTRFS_NESTING_NORMAL);
+}
+
 /*
  * Release the write lock, either blocking or spinning (ie. there's no need
  * for an explicit blocking unlock, like btrfs_tree_read_unlock_blocking).
@@ -565,7 +571,7 @@ struct extent_buffer *__btrfs_read_lock_root_node(struct btrfs_root *root,
 
 	while (1) {
 		eb = btrfs_root_node(root);
-		__btrfs_tree_read_lock(eb, recurse);
+		__btrfs_tree_read_lock(eb, BTRFS_NESTING_NORMAL, recurse);
 		if (eb == root->node)
 			break;
 		btrfs_tree_read_unlock(eb);

fs/btrfs/locking.h

@@ -16,12 +16,35 @@
 #define BTRFS_WRITE_LOCK_BLOCKING 3
 #define BTRFS_READ_LOCK_BLOCKING 4
 
+/*
+ * We are limited in number of subclasses by MAX_LOCKDEP_SUBCLASSES, which at
+ * the time of this patch is 8, which is how many we use.  Keep this in mind if
+ * you decide you want to add another subclass.
+ */
+enum btrfs_lock_nesting {
+	BTRFS_NESTING_NORMAL,
+
+	/*
+	 * We are limited to MAX_LOCKDEP_SUBLCLASSES number of subclasses, so
+	 * add this in here and add a static_assert to keep us from going over
+	 * the limit.  As of this writing we're limited to 8, and we're
+	 * definitely using 8, hence this check to keep us from messing up in
+	 * the future.
+	 */
+	BTRFS_NESTING_MAX,
+};
+
+static_assert(BTRFS_NESTING_MAX <= MAX_LOCKDEP_SUBCLASSES,
+	      "too many lock subclasses defined");
+
 struct btrfs_path;
 
+void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
 void btrfs_tree_lock(struct extent_buffer *eb);
 void btrfs_tree_unlock(struct extent_buffer *eb);
 
-void __btrfs_tree_read_lock(struct extent_buffer *eb, bool recurse);
+void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest,
+			    bool recurse);
 void btrfs_tree_read_lock(struct extent_buffer *eb);
 void btrfs_tree_read_unlock(struct extent_buffer *eb);
 void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb);