In commit 
1da177e4c3f4 ("Linux-2.6.12-rc2"), the helper allow_write_access
came with the atomic_inc operation of the i_writecount field in the func
__remove_shared_vm_struct().  But it forgot to use this helper function.
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: https://lkml.kernel.org/r/20200921115814.39680-1-linmiaohe@huawei.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
                struct file *file, struct address_space *mapping)
 {
        if (vma->vm_flags & VM_DENYWRITE)
-               atomic_inc(&file_inode(file)->i_writecount);
+               allow_write_access(file);
        if (vma->vm_flags & VM_SHARED)
                mapping_unmap_writable(mapping);