Re: [PATCH v9 06/10] iomap: fix iomap_dio_zero() for fs bs > system page size

Hannes Reinecke
2024-07-04T15:37:36Z

On 7/4/24 13:23, 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/buffered-io.c | 4 ++--
> fs/iomap/direct-io.c | 45 ++++++++++++++++++++++++++++++++++++------
> 2 files changed, 41 insertions(+), 8 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index f420c53d86acc..d745f718bcde8 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -2007,10 +2007,10 @@ iomap_writepages(struct address_space *mapping, struct writeback_control *wbc,
> }
> EXPORT_SYMBOL_GPL(iomap_writepages);
>
> -static int __init iomap_init(void)
> +static int __init iomap_buffered_init(void)
> {
> return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
> offsetof(struct iomap_ioend, io_bio),
> BIOSET_NEED_BVECS);
> }
> -fs_initcall(iomap_init);
> +fs_initcall(iomap_buffered_init);
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index f3b43d223a46e..c02b266bba525 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -11,6 +11,7 @@
> #include <linux/iomap.h>
> #include <linux/backing-dev.h>
> #include <linux/uio.h>
> +#include <linux/set_memory.h>
> #include <linux/task_io_accounting_ops.h>
> #include "trace.h"
>
> @@ -27,6 +28,13 @@
> #define IOMAP_DIO_WRITE (1U << 30)
> #define IOMAP_DIO_DIRTY (1U << 31)
>
> +/*
> + * Used for sub block zeroing in iomap_dio_zero()
> + */
> +#define IOMAP_ZERO_PAGE_SIZE (SZ_64K)
> +#define IOMAP_ZERO_PAGE_ORDER (get_order(IOMAP_ZERO_PAGE_SIZE))
> +static struct page *zero_page;
> +

There are other users of ZERO_PAGE, most notably in fs/direct-io.c and
block/blk-lib.c. Any chance to make this available to them?

Cheers,

Hannes
--
Dr. Hannes Reinecke Kernel Storage Architect
hare@suse.de +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich