On Mon, 23 Jun 2025, Mikulas Patocka wrote:
> Applied, thanks.
>
> Mikulas
Applied and reverted :)
I've just realized that this patch won't work because the value
get_max_request_size is changeable by the user - it's in the file
/sys/module/dm_crypt/parameters/max_write_size. So, if there is some large
value when you create the device and later the user sets smaller value,
dm-crypt will still split emulated zone append bios.
I suggest to set the limit limits->max_hw_sectors to BIO_MAX_VECS <<
PAGE_SHIFT (that's the maximum allowable value for dm-crypt) and then
modify dm-crypt to not split bios that have the flag
BIO_EMULATES_ZONE_APPEND.
Mikulas
> On Wed, 11 Jun 2025, Damien Le Moal wrote:
>
> > For a zoned dm-crypt device, the native support for zone append
> > operations (REQ_OP_ZONE_APPEND) is not enabled and instead dm-crypt
> > relies on the emulation done by the block layer using regular write
> > operations. This still requires to properly return the written sector as
> > the BIO sector of the original BIO. However, this can be done correctly
> > only and only if there is a single clone BIO used for processing the
> > original zone append operation issued by the user. If the size of a zone
> > append operation is larger than dm-crypt max_write_size, then the
> > orginal BIO will be split and processed as a chain of regular write
> > operations. Such chaining result in an incorrect written sector being
> > returned to the zone append issuer using the original BIO sector.
> > This in turn results in file system data corruptions using xfs or btrfs.
> >
> > Fix this by modifying crypt_io_hints() to cap the max_hw_sectors limit
> > for the dm-crypt device to the max_write_size limit. As this limit also
> > caps the device max_zone_append_sectors limit, this forces the caller to
> > issue zone append operations smaller than this limit, thus moving the
> > splitting of large append operations to the caller instead of the
> > incorrect internal splitting.
> >
> > This change does not have any effect on the size of BIOs received by
> > dm-crypt since the block layer does not automatically splits BIOs for
> > BIO-based devices. So there is no impact on the performance of regular
> > read and write operations.
> >
> > Fixes: f211268ed1f9 ("dm: Use the block layer zone append emulation")
> > Cc: sta...@vger.kernel.org
> > Signed-off-by: Damien Le Moal <dlem...@kernel.org>
> > ---
> > drivers/md/dm-crypt.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> > index 9dfdb63220d7..7b1e88781a82 100644
> > --- a/drivers/md/dm-crypt.c
> > +++ b/drivers/md/dm-crypt.c
> > @@ -3730,6 +3730,18 @@ static void crypt_io_hints(struct dm_target *ti,
> > struct queue_limits *limits)
> > max_t(unsigned int, limits->physical_block_size,
> > cc->sector_size);
> > limits->io_min = max_t(unsigned int, limits->io_min, cc->sector_size);
> > limits->dma_alignment = limits->logical_block_size - 1;
> > +
> > + /*
> > + * For zoned devices, we cannot split write operations used to emulate
> > + * zone append operations. And since all write requests are going to be
> > + * split on get_max_request_size(cc, true) size, apply this limit to the
> > + * maximum hardware I/O size so that we have a cap on the
> > + * max_zone_append_sectors limit when the zone limits are validated by
> > + * the block layer.
> > + */
> > + if (ti->emulate_zone_append)
> > + limits->max_hw_sectors = min(limits->max_hw_sectors,
> > + get_max_request_size(cc, true));
> > }
> >
> > static struct target_type crypt_target = {
> > --
> > 2.49.0
> >
>
