f2fs: use atomic variable for total_extent_tree

It would be better to use atomic variable for total_extent_tree.

Reviewed-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
index e86e9f1e..0e97d6af 100644
--- a/fs/f2fs/extent_cache.c
+++ b/fs/f2fs/extent_cache.c
@@ -70,7 +70,7 @@
 		rwlock_init(&et->lock);
 		atomic_set(&et->refcount, 0);
 		et->count = 0;
-		sbi->total_ext_tree++;
+		atomic_inc(&sbi->total_ext_tree);
 	}
 	atomic_inc(&et->refcount);
 	up_write(&sbi->extent_tree_lock);
@@ -570,7 +570,7 @@
 
 				radix_tree_delete(root, et->ino);
 				kmem_cache_free(extent_tree_slab, et);
-				sbi->total_ext_tree--;
+				atomic_dec(&sbi->total_ext_tree);
 				tree_cnt++;
 
 				if (node_cnt + tree_cnt >= nr_shrink)
@@ -663,7 +663,7 @@
 	f2fs_bug_on(sbi, atomic_read(&et->refcount) || et->count);
 	radix_tree_delete(&sbi->extent_tree_root, inode->i_ino);
 	kmem_cache_free(extent_tree_slab, et);
-	sbi->total_ext_tree--;
+	atomic_dec(&sbi->total_ext_tree);
 	up_write(&sbi->extent_tree_lock);
 
 	F2FS_I(inode)->extent_tree = NULL;
@@ -715,7 +715,7 @@
 	init_rwsem(&sbi->extent_tree_lock);
 	INIT_LIST_HEAD(&sbi->extent_list);
 	spin_lock_init(&sbi->extent_lock);
-	sbi->total_ext_tree = 0;
+	atomic_set(&sbi->total_ext_tree, 0);
 	atomic_set(&sbi->total_ext_node, 0);
 }