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

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Date: Mon, 1 Jul 2024 11:22:30 +0000
From: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
To: Dave Chinner <david@...morbit.com>
Cc: 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, hch@....de, Zi Yan <zi.yan@...t.com>
Subject: Re: [PATCH v8 06/10] iomap: fix iomap_dio_zero() for fs bs > system
 page size

On Mon, Jul 01, 2024 at 12:37:10PM +1000, Dave Chinner wrote:
> On Tue, Jun 25, 2024 at 11:44:16AM +0000, Pankaj Raghav (Samsung) wrote:
> > From: Pankaj Raghav <p.raghav@...sung.com>
> > 
> > iomap_dio_zero() will pad a fs block with zeroes if the direct IO size
> > < fs block size. iomap_dio_zero() has an implicit assumption that fs block
> > size < page_size. This is true for most filesystems at the moment.
> > 
> > If the block size > page size, this will send the contents of the page
> > next to zero page(as len > PAGE_SIZE) to the underlying block device,
> > causing FS corruption.
> > 
> > iomap is a generic infrastructure and it should not make any assumptions
> > about the fs block size and the page size of the system.
> > 
> > Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> > Reviewed-by: Hannes Reinecke <hare@...e.de>
> 
> Looks fine, so:
> 
> Reviewed-by: Dave Chinner <dchinner@...hat.com>
Thanks!
> 
> but....
> 
> > +
> > +	if (!zero_page_64k)
> > +		return -ENOMEM;
> > +
> > +	set_memory_ro((unsigned long)page_address(zero_page_64k),
> > +		      1U << ZERO_PAGE_64K_ORDER);
>                       ^^^^^^^^^^^^^^^^^^^^^^^^^
> isn't that just ZERO_PAGE_64K_SIZE?

Nope, set_memory_ro takes numbers of pages and not size in bytes :)

> 
> -Dave.
> -- 
> Dave Chinner
> david@...morbit.com