linux-kernel - Re: [PATCH v8 06/10] iomap: fix iomap_dio

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Message-ID: <20240702120250.GA17373@lst.de>
Date: Tue, 2 Jul 2024 14:02:50 +0200
From: Christoph Hellwig <hch@....de>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: Christoph Hellwig <hch@....de>, david@...morbit.com,
	willy@...radead.org, chandan.babu@...cle.com, djwong@...nel.org,
	brauner@...nel.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, yang@...amperecomputing.com,
	linux-mm@...ck.org, john.g.garry@...cle.com,
	linux-fsdevel@...r.kernel.org, hare@...e.de, p.raghav@...sung.com,
	mcgrof@...nel.org, gost.dev@...sung.com, cl@...amperecomputing.com,
	linux-xfs@...r.kernel.org, Zi Yan <zi.yan@...t.com>
Subject: Re: [PATCH v8 06/10] iomap: fix iomap_dio_zero() for fs bs >
 system page size

On Tue, Jul 02, 2024 at 10:15:56AM +0000, Pankaj Raghav (Samsung) wrote:
> Willy suggested we could use raw pages as we don't need the metadata
> from using a folio. [0]

Ok, that feels weird but I'll defer to his opinion in that case.

> > > +	/*
> > > +	 * Max block size supported is 64k
> > > +	 */
> > > +	WARN_ON_ONCE(len > ZERO_PAGE_64K_SIZE);
> > 
> > 
> > A WARN_ON without actually erroring out here is highly dangerous. 
> 
> I agree but I think we decided that we are safe with 64k for now as fs 
> that uses iomap will not have a block size > 64k. 
> 
> But this function needs some changes when we decide to go beyond 64k
> by returning error instead of not returning anything. 
> Until then WARN_ON_ONCE would be a good stop gap for people developing
> the feature to go beyond 64k block size[1]. 

Sure, but please make it return an error and return that instead of
just warning and going beyond the allocated page.