linux-kernel - Re: [PATCH v9 06/10] iomap: fix iomap_dio

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Message-ID: <2c09ebbd-1704-46e3-a453-b4cd07940325@suse.de>
Date: Thu, 4 Jul 2024 17:37:32 +0200
From: Hannes Reinecke <hare@...e.de>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>, david@...morbit.com,
 willy@...radead.org, chandan.babu@...cle.com, djwong@...nel.org,
 brauner@...nel.org, akpm@...ux-foundation.org
Cc: yang@...amperecomputing.com, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, john.g.garry@...cle.com, linux-fsdevel@...r.kernel.org,
 p.raghav@...sung.com, mcgrof@...nel.org, gost.dev@...sung.com,
 cl@...amperecomputing.com, linux-xfs@...r.kernel.org, hch@....de,
 Zi Yan <ziy@...dia.com>
Subject: Re: [PATCH v9 06/10] iomap: fix iomap_dio_zero() for fs bs > system
 page size

On 7/4/24 13:23, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@...sung.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@...sung.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@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich