Re: [PATCH v3 1/3] kernfs: remove page_mkwrite() from vm_operations_struct

[Matthew Wilcox]

On Thu, Jul 04, 2024 at 10:37:22AM -0600, Martin Oliveira wrote:
> @@ -482,6 +459,8 @@ static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
>  	if (vma->vm_ops && vma->vm_ops->close)
>  		goto out_put;
>  
> +	WARN_ON(vma->vm_ops && vma->vm_ops->page_mkwrite);
> +
>  	rc = 0;
>  	if (!of->mmapped) {
>  		of->mmapped = true;

Seems to me we should actually _handle_ that, not do something wrong.
eg:

	if (vma->vm_ops) {
		if (vma->vm_ops->close)
			goto out_put;
		if (WARN_ON(vma->vm_ops->page_mkwrite))
			goto out_put;
	}

or maybe this doesn't need to be a WARN at all?  After all, there
isn't one for having a ->close method, so why is page_mkwrite special?