static int ext4_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
{
	int err;
	struct inode *inode = file_inode(vma->vm_file);

	sb_start_pagefault(inode->i_sb);
	file_update_time(vma->vm_file);
	down_read(&EXT4_I(inode)->i_mmap_sem);
	err = __dax_mkwrite(vma, vmf, ext4_get_block_dax,
			    ext4_end_io_unwritten);
	up_read(&EXT4_I(inode)->i_mmap_sem);
	sb_end_pagefault(inode->i_sb);

	return err;
}
The program contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.