Re: [PATCH v8 06/10] iomap: fix iomap_dio_zero() for fs bs > system page size

Pankaj Raghav (Samsung)
2024-07-01T11:22:46Z

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@samsung.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@samsung.com>
> > Reviewed-by: Hannes Reinecke <hare@suse.de>
>
> Looks fine, so:
>
> Reviewed-by: Dave Chinner <dchinner@redhat.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@fromorbit.com