Re: [PATCH 1/2] block: Make __submit_bio_noacct() preserve the bio submission order

[Damien Le Moal <dlemoal@kernel.org>]

On 5/23/25 18:30, Bart Van Assche wrote:
> On 5/22/25 11:02 PM, Damien Le Moal wrote:
>> On 5/22/25 19:08, Bart Van Assche wrote:
>  > [ ... ]
>> Which DM driver is it ? Does that DM driver have some special work queue
>> handling of BIO submissions ? Or does is simply remap the BIO and send it down
>> to the underlying device in the initial submit_bio() context ? If it is the
>> former case, then that DM driver must enable zone write plugging. If it is the
>> latter, it should not need zone write plugging and ordering will be handled
>> correctly throughout the submit_bio() context for the initial DM BIO, assuming
>> that the submitter does indeed serialize write BIO submissions to a zone. I have
>> not looked at f2fs code in ages. When I worked on it, there was a mutex to
>> serialize write issuing to avoid reordering issues...
> 
> It is the dm-default-key driver, a driver about which everyone
> (including the authors of that driver) agree that it should disappear.
> Unfortunately the functionality provided by that driver has not yet been
> integrated in the upstream kernel (encrypt filesystem metadata).
> 
> How that driver (dm-default-key) works is very similar to how dm-crypt
> works. I think that the most important difference is that dm-crypt
> requests encryption for all bios while dm-default-key only sets an
> encryption key for a subset of the bios it processes.
> 
> The source code of that driver is available here:
> https://android.googlesource.com/kernel/common/+/refs/heads/android16-6.12/drivers/md/dm-default-key.c

Well, this is an out of tree driver. Not touching this.
Unless you can reproduce the issue with dm-crypt (or any other DM target that is
upstream), I will not even try to debug this.

Note that our internal test suite runs *lots* of different zoned devices (SMR
HDD, ZNS SSDs, nullblk, tcmu-runner ZBC device, scsi_debug, qemu nvme zns
device) against *lots* of configurations for file systems (xfs, btrfs, zonefs)
and DM targets (dm-crypt, dm-linear) and we have not seen any reordering issue,
We run this test suite weekly against RC kernels and for-next branch.


-- 
Damien Le Moal
Western Digital Research