btrfs: introduce BTRFS_NESTING_LEFT/RIGHT_COW

For similar reasons as BTRFS_NESTING_COW, we need
BTRFS_NESTING_LEFT/RIGHT_COW.  The pattern is this

lock leaf -> BTRFS_NESTING_NORMAL
  cow leaf -> BTRFS_NESTING_COW
    split leaf
      lock left -> BTRFS_NESTING_LEFT
        cow left -> BTRFS_NESTING_LEFT_COW

We need this in order to indicate to lockdep that these locks are
discrete and are being taken in a safe order.
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

@@ -1900,7 +1900,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 		btrfs_set_lock_blocking_write(left);
 		wret = btrfs_cow_block(trans, root, left,
 				       parent, pslot - 1, &left,
-				       BTRFS_NESTING_COW);
+				       BTRFS_NESTING_LEFT_COW);
 		if (wret) {
 			ret = wret;
 			goto enospc;
@@ -1916,7 +1916,7 @@ static noinline int balance_level(struct btrfs_trans_handle *trans,
 		btrfs_set_lock_blocking_write(right);
 		wret = btrfs_cow_block(trans, root, right,
 				       parent, pslot + 1, &right,
-				       BTRFS_NESTING_COW);
+				       BTRFS_NESTING_RIGHT_COW);
 		if (wret) {
 			ret = wret;
 			goto enospc;
@@ -2085,7 +2085,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 		} else {
 			ret = btrfs_cow_block(trans, root, left, parent,
 					      pslot - 1, &left,
-					      BTRFS_NESTING_COW);
+					      BTRFS_NESTING_LEFT_COW);
 			if (ret)
 				wret = 1;
 			else {
@@ -2140,7 +2140,7 @@ static noinline int push_nodes_for_insert(struct btrfs_trans_handle *trans,
 		} else {
 			ret = btrfs_cow_block(trans, root, right,
 					      parent, pslot + 1,
-					      &right, BTRFS_NESTING_COW);
+					      &right, BTRFS_NESTING_RIGHT_COW);
 			if (ret)
 				wret = 1;
 			else {
@@ -3815,7 +3815,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
 
 	/* cow and double check */
 	ret = btrfs_cow_block(trans, root, right, upper,
-			      slot + 1, &right, BTRFS_NESTING_COW);
+			      slot + 1, &right, BTRFS_NESTING_RIGHT_COW);
 	if (ret)
 		goto out_unlock;
 
@@ -4057,7 +4057,7 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
 	/* cow and double check */
 	ret = btrfs_cow_block(trans, root, left,
 			      path->nodes[1], slot - 1, &left,
-			      BTRFS_NESTING_COW);
+			      BTRFS_NESTING_LEFT_COW);
 	if (ret) {
 		/* we hit -ENOSPC, but it isn't fatal here */
 		if (ret == -ENOSPC)

fs/btrfs/locking.h

@@ -44,6 +44,14 @@ enum btrfs_lock_nesting {
 	BTRFS_NESTING_LEFT,
 	BTRFS_NESTING_RIGHT,
 
+	/*
+	 * When splitting we will be holding a lock on the left/right node when
+	 * we need to cow that node, thus we need a new set of subclasses for
+	 * these two operations.
+	 */
+	BTRFS_NESTING_LEFT_COW,
+	BTRFS_NESTING_RIGHT_COW,
+
 	/*
 	 * 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