Re: [PATCH] dm-crypt: defer async write submission to write thread

[Josef Schlehofer <pepe.schlehofer@gmail.com>]

On Mon, 9 Nov 2026, Mikulas Patocka wrote:
> On Mon, 9 Nov 2026, Damien Le Moal wrote:
>> Originally, this was added to avoid write reordering for zoned block devices.
>> So did you test this change with that (scsi_debug or null-blk) ? You can also
>> use an emulated NVMe ZNS device in QEMU.
>
> So, should we disable asynchronous crypto operations for zoned devices?

I tested dm-7.4 with and without the patch in QEMU, using null_blk,
scsi_debug and an emulated ZNS device. I tested both cryptd and a
synchronous cipher.

My write and read-back checks passed on both arm64 and x86_64. I also
ran fio's t/zbd suite and blktests zbd on arm64. All tests passed with
both kernels.

I also used a kprobe to check whether async=1 was ever used in
kcryptd_crypt_write_io_submit() on zoned devices. It wasn't, since
DM_CRYPT_WRITE_INLINE keeps those writes on the async=0 path.

The only exception was blktests zbd/013, which stalled during cleanup on
both kernels under heavy host load. The LUKS volume was still mapped
after luksClose, causing null_blk unloading to wait.

I couldn't find any issues with this change or with async crypto on
zoned devices, so whether to disable it is up to you and Damien.

Thanks,
Josef