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

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Message-ID: <Zoeew3RMOoUIMHz9@infradead.org>
Date: Fri, 5 Jul 2024 00:20:35 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Martin Oliveira <martin.oliveira@...eticom.com>
Cc: Matthew Wilcox <willy@...radead.org>, 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>,
	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 02:43:04PM -0600, Martin Oliveira wrote:
> On 2024-07-04 11:02, Matthew Wilcox wrote:> 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;
> >         }
> 
> Good point.

Btw, sorry if I mislead you with my WARN_ON_ONCE suggestion.  That
was always intended in addition to the error handling, not instead.
(In fact there are very few reasons to use WARN_ON* without actually
handling the error as well).

> 
> > 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?
> 
> Hmm yeah, they should probably be treated the same.
> 
> Maybe ->close should be converted to WARN as well? It would be easier to
> catch an error this way than chasing the EINVAL, but I'm OK either way.

Yes, doing the same for ->close or anything unimplemented would be
nice.  But it's not really in scope for this series.

kernfs really should be using it's own ops instead of abusing
file_operations, but that's even more out of scope..