diff --git a/kernel/fork.c b/kernel/fork.c
index fa91243..1380d8a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -429,7 +429,7 @@
 				atomic_dec(&inode->i_writecount);
 			mutex_lock(&mapping->i_mmap_mutex);
 			if (tmp->vm_flags & VM_SHARED)
-				mapping->i_mmap_writable++;
+				atomic_inc(&mapping->i_mmap_writable);
 			flush_dcache_mmap_lock(mapping);
 			/* insert tmp into the share list, just after mpnt */
 			if (unlikely(tmp->vm_flags & VM_NONLINEAR))