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

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Message-ID: <da1d2eea-b7b1-467c-84e0-623d4ec3af55@suse.de>
Date: Fri, 5 Jul 2024 08:14:57 +0200
From: Hannes Reinecke <hare@...e.de>
To: Dave Chinner <david@...morbit.com>
Cc: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>, willy@...radead.org,
 chandan.babu@...cle.com, djwong@...nel.org, brauner@...nel.org,
 akpm@...ux-foundation.org, 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 7/5/24 00:13, Dave Chinner wrote:
> On Thu, Jul 04, 2024 at 05:37:32PM +0200, Hannes Reinecke wrote:
>> 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?
> 
> Please, no.
> 
> We need to stop feature creeping this patchset and bring it to a
> close. If changing code entirely unrelated to this patchset is
> desired, please do it as a separate independent set of patches.
> 
Agree; it was a suggestion only.

Pankaj, you can add my:

Reviewed-by: Hannes Reinecke <hare@...e.de>

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