Re: [RFC v2 10/14] iomap: fix iomap_dio_zero() for fs bs > system page size

Darrick J. Wong
2024-02-13T21:30:41Z

On Tue, Feb 13, 2024 at 10:27:32PM +0100, Pankaj Raghav (Samsung) wrote:
> On Tue, Feb 13, 2024 at 08:30:37AM -0800, Darrick J. Wong wrote:
> > On Tue, Feb 13, 2024 at 10:37:09AM +0100, 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>
> > > ---
> > > fs/iomap/direct-io.c | 13 +++++++++++--
> > > 1 file changed, 11 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> > > index bcd3f8cf5ea4..04f6c5548136 100644
> > > --- a/fs/iomap/direct-io.c
> > > +++ b/fs/iomap/direct-io.c
> > > @@ -239,14 +239,23 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
> > > struct page *page = ZERO_PAGE(0);
> > > struct bio *bio;
> > >
> > > - bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
> > > + WARN_ON_ONCE(len > (BIO_MAX_VECS * PAGE_SIZE));
> > > +
> > > + bio = iomap_dio_alloc_bio(iter, dio, BIO_MAX_VECS,
> > > + REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
> > > fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
> > > GFP_KERNEL);
> > > +
> > > bio->bi_iter.bi_sector = iomap_sector(&iter->iomap, pos);
> > > bio->bi_private = dio;
> > > bio->bi_end_io = iomap_dio_bio_end_io;
> > >
> > > - __bio_add_page(bio, page, len, 0);
> > > + while (len) {
> > > + unsigned int io_len = min_t(unsigned int, len, PAGE_SIZE);
> >
> > What was the result of all that discussion about using the PMD-sized
> > zero-folio the last time this patch was submitted? Did that prove to be
> > unwieldly, or did it require enough extra surgery to become its own
> > series?
> >
>
> It proved a bit unwieldly to me at least as I did not know any straight
> forward way to do it at the time. So I thought I will keep this approach
> as it is, and add support for the PMD-sized zero folio for later
> improvement.
>
> > (The code here looks good to me.)
>
> Thanks!

In that case I'll throw it on the testing pile and let's ask brauner to
merge this for 6.9 if nothing blows up.

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> >
> > --D
> >
> > > +
> > > + __bio_add_page(bio, page, io_len, 0);
> > > + len -= io_len;
> > > + }
> > > iomap_dio_submit_bio(iter, dio, bio, pos);
> > > }
> > >
> > > --
> > > 2.43.0
> > >
> > >
>