Re: [PATCH v7 07/11] iomap: fix iomap_dio_zero() for fs bs > system page size

Darrick J. Wong
2024-06-12T20:40:26Z

On Fri, Jun 07, 2024 at 02:58:58PM +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>
> ---
> fs/internal.h | 5 +++++
> fs/iomap/buffered-io.c | 6 ++++++
> fs/iomap/direct-io.c | 26 ++++++++++++++++++++++++--
> 3 files changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/fs/internal.h b/fs/internal.h
> index 84f371193f74..30217f0ff4c6 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -35,6 +35,11 @@ static inline void bdev_cache_init(void)
> int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
> get_block_t *get_block, const struct iomap *iomap);
>
> +/*
> + * iomap/direct-io.c
> + */
> +int iomap_dio_init(void);
> +
> /*
> * char_dev.c
> */
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 49938419fcc7..9f791db473e4 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -1990,6 +1990,12 @@ EXPORT_SYMBOL_GPL(iomap_writepages);
>
> static int __init iomap_init(void)
> {
> + int ret;
> +
> + ret = iomap_dio_init();
> + if (ret)
> + return ret;
> +
> return bioset_init(&iomap_ioend_bioset, 4 * (PAGE_SIZE / SECTOR_SIZE),
> offsetof(struct iomap_ioend, io_bio),
> BIOSET_NEED_BVECS);
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index f3b43d223a46..b95600b254a3 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -27,6 +27,13 @@
> #define IOMAP_DIO_WRITE (1U << 30)
> #define IOMAP_DIO_DIRTY (1U << 31)
>
> +/*
> + * Used for sub block zeroing in iomap_dio_zero()
> + */
> +#define ZERO_FSB_SIZE (65536)
> +#define ZERO_FSB_ORDER (get_order(ZERO_FSB_SIZE))
> +static struct page *zero_fs_block;

Er... zero_page_64k ?

Since it's a permanent allocation, can we also mark the memory ro?

> +
> struct iomap_dio {
> struct kiocb *iocb;
> const struct iomap_dio_ops *dops;
> @@ -52,6 +59,16 @@ struct iomap_dio {
> };
> };
>
> +int iomap_dio_init(void)
> +{
> + zero_fs_block = alloc_pages(GFP_KERNEL | __GFP_ZERO, ZERO_FSB_ORDER);
> +
> + if (!zero_fs_block)
> + return -ENOMEM;
> +
> + return 0;
> +}

Can't we just turn this into another fs_initcall() instead of exporting
it just so we can call it from iomap_init? And maybe rename the
existing iomap_init to iomap_pagecache_init or something, for clarity's
sake?

--D

> +
> static struct bio *iomap_dio_alloc_bio(const struct iomap_iter *iter,
> struct iomap_dio *dio, unsigned short nr_vecs, blk_opf_t opf)
> {
> @@ -236,17 +253,22 @@ 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_FSB_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);
> +
> 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);
> + __bio_add_page(bio, zero_fs_block, len, 0);
> iomap_dio_submit_bio(iter, dio, bio, pos);
> }
>
> --
> 2.44.1
>
>