Re: [PATCH v5 09/10] scsi: scsi_debug: Map the region written by WRITE ATOMIC (16)

[John Garry <john.garry@linux.dev>]

On 9/21/26 16:40, Niklas Cassel wrote:
> When logical block provisioning is enabled, a command that writes user
> data marks the region that it wrote in the provisioning map, so that
> GET LBA STATUS reports the region as mapped. resp_write_dt0(),
> resp_write_scat() and resp_write_same() all call map_region() for that.
> 
> resp_atomic_write() does not, so a WRITE ATOMIC (16) leaves the
> provisioning map untouched, and GET LBA STATUS keeps reporting the
> region as deallocated after it has been written. map_state(), which
> GET LBA STATUS uses, is the only reader of the map, so that is the whole
> of the effect.
> 
> Call map_region() the way resp_write_dt0() does, and take the zone
> metadata write lock across the access as it does when logical block
> provisioning is enabled. That lock is what serialises the provisioning
> map against resp_unmap(), which holds it while unmap_region() clears map
> bits and zeroes the data that they cover. resp_unmap() does nothing
> unless logical block provisioning is enabled, so the lock is only needed
> in that case.
> 
> Assisted-by: LLM
> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
> Fixes: 84f3a3c01d70 ("scsi: scsi_debug: Atomic write support")
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> ---
> Tested with:
> 
>    modprobe scsi_debug sector_size=512 physblk_exp=3 dev_size_mb=128 \
>        atomic_wr=1 lbpu=1
> 
> GET LBA STATUS reports a region that has never been written as
> deallocated, and reports it as mapped after a WRITE ATOMIC (16) of eight
> blocks. Only an ordinary WRITE did so before this patch.
> ---
> 
> Changes since v4: the meta_data_locked variable is gone, as suggested.
>   drivers/scsi/scsi_debug.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index d07f6f891951..2e1a02c383a3 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -6202,6 +6202,7 @@ static int resp_atomic_write(struct scsi_cmnd *scp,
>   	u8 *cmd = scp->cmnd;
>   	u16 boundary, len;
>   	u64 lba, lba_tmp;
> +	bool lbp = scsi_debug_lbp();
>   	int ret;
>   
>   	if (!scsi_debug_atomic_write()) {
> @@ -6246,7 +6247,16 @@ static int resp_atomic_write(struct scsi_cmnd *scp,
>   		}
>   	}
>   
> +	if (lbp)
> +		sdeb_meta_write_lock(sip);
> +
>   	ret = do_device_access(sip, scp, 0, lba, len, 0, true, true);
> +	if (unlikely(lbp))

Is this supposed to be called if ret <= 0?

> +		map_region(sip, lba, len);
> +
> +	if (lbp)

Ignoring comment above, why not combine into a single if statement?

> +		sdeb_meta_write_unlock(sip);
 > +>   	if (unlikely(ret == -1))
>   		return DID_ERROR << 16;
>   	if (unlikely(ret != len * sdebug_sector_size))