Re: Re: [PATCH AUTOSEL 6.11 237/244] iomap: fix iomap_dio_zero() for fs bs > system page size

Pankaj Raghav (Samsung)
2024-09-26T07:58:47Z

On Wed, Sep 25, 2024 at 11:01:46PM +1000, Dave Chinner wrote:
> On Wed, Sep 25, 2024 at 07:27:38AM -0400, Sasha Levin wrote:
> > From: Pankaj Raghav <p.raghav@samsung.com>
> >
> > [ Upstream commit 10553a91652d995274da63fc317470f703765081 ]
> >
> > 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.
>
> Please drop this. It is for support of new functionality that was
> just merged and has no relevance to older kernels. It is not a bug
> fix.
>

I did not have any fixes by tag for this reason. So please drop this commit
from the queue.

> And ....
>
> > +
> > + set_memory_ro((unsigned long)page_address(zero_page),
> > + 1U << IOMAP_ZERO_PAGE_ORDER);
>
> .... this will cause stable kernel regressions.
>
> It was removed later in the merge because it is unnecessary and
> causes boot failures on (at least) some Power architectures.
>
> -Dave.
> --
> Dave Chinner
> david@fromorbit.com

--
Pankaj Raghav