linux-kernel - Re: [PATCH v3 1/3] kernfs: remove page_mkwrite() from vm_operations

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Message-ID: <ZobVol_trCwtwjK4@casper.infradead.org>
Date: Thu, 4 Jul 2024 18:02:26 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Martin Oliveira <martin.oliveira@...eticom.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-rdma@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Artemy Kovalyov <artemyko@...dia.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jason Gunthorpe <jgg@...pe.ca>, Leon Romanovsky <leon@...nel.org>,
	Logan Gunthorpe <logang@...tatee.com>,
	Michael Guralnik <michaelgur@...dia.com>,
	Mike Marciniszyn <mike.marciniszyn@...el.com>,
	Shiraz Saleem <shiraz.saleem@...el.com>, Tejun Heo <tj@...nel.org>,
	John Hubbard <jhubbard@...dia.com>,
	Dan Williams <dan.j.williams@...el.com>,
	David Sloan <david.sloan@...eticom.com>
Subject: Re: [PATCH v3 1/3] kernfs: remove page_mkwrite() from
 vm_operations_struct

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?