btrfs: add tracepoints for outstanding extents mods

This is handy for tracing problems with modifying the outstanding
extents counters.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index bed8881..427c873 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -274,6 +274,8 @@
 	inode->outstanding_extents += mod;
 	if (btrfs_is_free_space_inode(inode))
 		return;
+	trace_btrfs_inode_mod_outstanding_extents(inode->root, btrfs_ino(inode),
+						  mod);
 }
 
 static inline void btrfs_mod_reserved_extents(struct btrfs_inode *inode, int mod)