Re: [dm-devel] [PATCHv2 0/5] fix direct io device mapper errors

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Nov 10 2022 at  1:44P -0500,
Keith Busch <kbusch@meta.com> wrote:

> From: Keith Busch <kbusch@kernel.org>
> 
> The 6.0 kernel made some changes to the direct io interface to allow
> offsets in user addresses. This based on the hardware's capabilities
> reported in the request_queue's dma_alignment attribute.
> 
> dm-crypt, -log-writes and -integrity require direct io be aligned to the
> block size. Since it was only ever using the default 511 dma mask, this
> requirement may fail if formatted to something larger, like 4k, which
> will result in unexpected behavior with direct-io.
> 
> Changes since v1: Added the same fix for -integrity and -log-writes
> 
> The first three were reported successfully tested by Dmitrii Tcvetkov,
> but I don't have an official Tested-by: tag.
> 
>   https://lore.kernel.org/linux-block/20221103194140.06ce3d36@xps.demsh.org/T/#mba1d0b13374541cdad3b669ec4257a11301d1860
> 
> Keitio errors on Busch (5):
>   block: make dma_alignment a stacking queue_limit
>   dm-crypt: provide dma_alignment limit in io_hints
>   block: make blk_set_default_limits() private
>   dm-integrity: set dma_alignment limit in io_hints
>   dm-log-writes: set dma_alignment limit in io_hints
> 
>  block/blk-core.c           |  1 -
>  block/blk-settings.c       |  9 +++++----
>  block/blk.h                |  1 +
>  drivers/md/dm-crypt.c      |  1 +
>  drivers/md/dm-integrity.c  |  1 +
>  drivers/md/dm-log-writes.c |  1 +
>  include/linux/blkdev.h     | 16 ++++++++--------
>  7 files changed, 17 insertions(+), 13 deletions(-)
> 
> -- 
> 2.30.2
> 

There are other DM targets that override logical_block_size in their
.io_hints hook (writecache, ebs, zoned). Have you reasoned through why
those do _not_ need updating too?

Is there any risk of just introducing a finalization method in block
core (that DM's .io_hints would call) that would ensure limits that
are a funtion of another are always in sync?  Would avoid whack-a-mole
issues in the future.

Thanks,
Mike

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