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

Darrick J. Wong
2024-07-01T23:40:09Z

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 good to me,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
> fs/iomap/buffered-io.c | 4 ++--
> fs/iomap/direct-io.c | 30 ++++++++++++++++++++++++++++--
> 2 files changed, 30 insertions(+), 4 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index f420c53d86ac..9a9e94c7ed1d 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_pagecache_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_pagecache_init);
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index f3b43d223a46..61d09d2364f7 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 ZERO_PAGE_64K_SIZE (65536)
> +#define ZERO_PAGE_64K_ORDER (get_order(ZERO_PAGE_64K_SIZE))
> +static struct page *zero_page_64k;
> +
> struct iomap_dio {
> struct kiocb *iocb;
> const struct iomap_dio_ops *dops;
> @@ -236,9 +244,13 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
> loff_t pos, unsigned len)
> {
> struct inode *inode = file_inode(dio->iocb->ki_filp);
> - struct page *page = ZERO_PAGE(0);
> struct bio *bio;
>
> + /*
> + * Max block size supported is 64k
> + */
> + WARN_ON_ONCE(len > ZERO_PAGE_64K_SIZE);
> +
> bio = iomap_dio_alloc_bio(iter, dio, 1, REQ_OP_WRITE | REQ_SYNC | REQ_IDLE);
> fscrypt_set_bio_crypt_ctx(bio, inode, pos >> inode->i_blkbits,
> GFP_KERNEL);
> @@ -246,7 +258,7 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
> bio->bi_private = dio;
> bio->bi_end_io = iomap_dio_bio_end_io;
>
> - __bio_add_page(bio, page, len, 0);
> + __bio_add_page(bio, zero_page_64k, len, 0);
> iomap_dio_submit_bio(iter, dio, bio, pos);
> }
>
> @@ -753,3 +765,17 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
> return iomap_dio_complete(dio);
> }
> EXPORT_SYMBOL_GPL(iomap_dio_rw);
> +
> +static int __init iomap_dio_init(void)
> +{
> + zero_page_64k = alloc_pages(GFP_KERNEL | __GFP_ZERO,
> + ZERO_PAGE_64K_ORDER);
> +
> + if (!zero_page_64k)
> + return -ENOMEM;
> +
> + set_memory_ro((unsigned long)page_address(zero_page_64k),
> + 1U << ZERO_PAGE_64K_ORDER);
> + return 0;
> +}
> +fs_initcall(iomap_dio_init);
> --
> 2.44.1
>
>