[PATCH] Rescan the entire target on transport reset when LUN is 0

[PATCH] Rescan the entire target on transport reset when LUN is 0

[Matej Genci]

VirtIO 1.0 spec says
    The removed and rescan events ... when sent for LUN 0, they MAY
    apply to the entire target so the driver can ask the initiator
    to rescan the target to detect this.

This change introduces the behaviour described above by scanning the
entire scsi target when LUN is set to 0. This is both a functional and a
performance fix. It aligns the driver with the spec and allows control
planes to hotplug targets with large numbers of LUNs without having to
request a RESCAN for each one of them.

Signed-off-by: Matej Genci <matej@nutanix.com>
Suggested-by: Felipe Franciosi <felipe@nutanix.com>
---
 drivers/scsi/virtio_scsi.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index bfec84aacd90..a4b9bc7b4b4a 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -284,7 +284,12 @@ static void virtscsi_handle_transport_reset(struct virtio_scsi *vscsi,
 
 	switch (virtio32_to_cpu(vscsi->vdev, event->reason)) {
 	case VIRTIO_SCSI_EVT_RESET_RESCAN:
-		scsi_add_device(shost, 0, target, lun);
+		if (lun == 0) {
+			scsi_scan_target(&shost->shost_gendev, 0, target,
+					 SCAN_WILD_CARD, SCSI_SCAN_INITIAL);
+		} else {
+			scsi_add_device(shost, 0, target, lun);
+		}
 		break;
 	case VIRTIO_SCSI_EVT_RESET_REMOVED:
 		sdev = scsi_device_lookup(shost, 0, target, lun);
-- 
2.20.1

Re: [PATCH] Rescan the entire target on transport reset when LUN is 0

[Michael S. Tsirkin]

On Fri, Aug 28, 2020 at 12:21:35PM +0000, Matej Genci wrote:
> VirtIO 1.0 spec says
>     The removed and rescan events ... when sent for LUN 0, they MAY
>     apply to the entire target so the driver can ask the initiator
>     to rescan the target to detect this.
> 
> This change introduces the behaviour described above by scanning the
> entire scsi target when LUN is set to 0. This is both a functional and a
> performance fix. It aligns the driver with the spec and allows control
> planes to hotplug targets with large numbers of LUNs without having to
> request a RESCAN for each one of them.
> 
> Signed-off-by: Matej Genci <matej@nutanix.com>
> Suggested-by: Felipe Franciosi <felipe@nutanix.com>

Stefan, Paolo, could you review this pls?

> ---
>  drivers/scsi/virtio_scsi.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> index bfec84aacd90..a4b9bc7b4b4a 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -284,7 +284,12 @@ static void virtscsi_handle_transport_reset(struct virtio_scsi *vscsi,
>  
>  	switch (virtio32_to_cpu(vscsi->vdev, event->reason)) {
>  	case VIRTIO_SCSI_EVT_RESET_RESCAN:
> -		scsi_add_device(shost, 0, target, lun);
> +		if (lun == 0) {
> +			scsi_scan_target(&shost->shost_gendev, 0, target,
> +					 SCAN_WILD_CARD, SCSI_SCAN_INITIAL);
> +		} else {
> +			scsi_add_device(shost, 0, target, lun);
> +		}
>  		break;
>  	case VIRTIO_SCSI_EVT_RESET_REMOVED:
>  		sdev = scsi_device_lookup(shost, 0, target, lun);
> -- 
> 2.20.1

Re: [PATCH] Rescan the entire target on transport reset when LUN is 0

[Paolo Bonzini]

On 28/08/20 14:21, Matej Genci wrote:
> VirtIO 1.0 spec says
>     The removed and rescan events ... when sent for LUN 0, they MAY
>     apply to the entire target so the driver can ask the initiator
>     to rescan the target to detect this.
> 
> This change introduces the behaviour described above by scanning the
> entire scsi target when LUN is set to 0. This is both a functional and a
> performance fix. It aligns the driver with the spec and allows control
> planes to hotplug targets with large numbers of LUNs without having to
> request a RESCAN for each one of them.
> 
> Signed-off-by: Matej Genci <matej@nutanix.com>
> Suggested-by: Felipe Franciosi <felipe@nutanix.com>
> ---
>  drivers/scsi/virtio_scsi.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> index bfec84aacd90..a4b9bc7b4b4a 100644
> --- a/drivers/scsi/virtio_scsi.c
> +++ b/drivers/scsi/virtio_scsi.c
> @@ -284,7 +284,12 @@ static void virtscsi_handle_transport_reset(struct virtio_scsi *vscsi,
>  
>  	switch (virtio32_to_cpu(vscsi->vdev, event->reason)) {
>  	case VIRTIO_SCSI_EVT_RESET_RESCAN:
> -		scsi_add_device(shost, 0, target, lun);
> +		if (lun == 0) {
> +			scsi_scan_target(&shost->shost_gendev, 0, target,
> +					 SCAN_WILD_CARD, SCSI_SCAN_INITIAL);
> +		} else {
> +			scsi_add_device(shost, 0, target, lun);
> +		}
>  		break;
>  	case VIRTIO_SCSI_EVT_RESET_REMOVED:
>  		sdev = scsi_device_lookup(shost, 0, target, lun);
> 


Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Re: [PATCH] Rescan the entire target on transport reset when LUN is 0

[Felipe Franciosi]

> On Sep 8, 2020, at 3:22 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> On 28/08/20 14:21, Matej Genci wrote:
>> VirtIO 1.0 spec says
>>    The removed and rescan events ... when sent for LUN 0, they MAY
>>    apply to the entire target so the driver can ask the initiator
>>    to rescan the target to detect this.
>> 
>> This change introduces the behaviour described above by scanning the
>> entire scsi target when LUN is set to 0. This is both a functional and a
>> performance fix. It aligns the driver with the spec and allows control
>> planes to hotplug targets with large numbers of LUNs without having to
>> request a RESCAN for each one of them.
>> 
>> Signed-off-by: Matej Genci <matej@nutanix.com>
>> Suggested-by: Felipe Franciosi <felipe@nutanix.com>
>> ---
>> drivers/scsi/virtio_scsi.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
>> index bfec84aacd90..a4b9bc7b4b4a 100644
>> --- a/drivers/scsi/virtio_scsi.c
>> +++ b/drivers/scsi/virtio_scsi.c
>> @@ -284,7 +284,12 @@ static void virtscsi_handle_transport_reset(struct virtio_scsi *vscsi,
>> 
>> 	switch (virtio32_to_cpu(vscsi->vdev, event->reason)) {
>> 	case VIRTIO_SCSI_EVT_RESET_RESCAN:
>> -		scsi_add_device(shost, 0, target, lun);
>> +		if (lun == 0) {
>> +			scsi_scan_target(&shost->shost_gendev, 0, target,
>> +					 SCAN_WILD_CARD, SCSI_SCAN_INITIAL);
>> +		} else {
>> +			scsi_add_device(shost, 0, target, lun);
>> +		}
>> 		break;
>> 	case VIRTIO_SCSI_EVT_RESET_REMOVED:
>> 		sdev = scsi_device_lookup(shost, 0, target, lun);
>> 
> 
> 
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Cc: stable@vger.kernel.org

Thanks, Paolo.

I'm Cc'ing stable as I believe this fixes a driver bug where it
doesn't follow the spec. Per commit message, today devices are
required to issue RESCAN events for each LUN behind a target when
hotplugging, or risking the driver not seeing the new LUNs.

Is this enough? Or should we resend after merge per below?
https://www.kernel.org/doc/Documentation/process/stable-kernel-rules.rst

F.

Re: [PATCH] Rescan the entire target on transport reset when LUN is 0

[Greg KH]

On Tue, Sep 08, 2020 at 05:53:16PM +0000, Felipe Franciosi wrote:
> 
> 
> > On Sep 8, 2020, at 3:22 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> > 
> > On 28/08/20 14:21, Matej Genci wrote:
> >> VirtIO 1.0 spec says
> >>    The removed and rescan events ... when sent for LUN 0, they MAY
> >>    apply to the entire target so the driver can ask the initiator
> >>    to rescan the target to detect this.
> >> 
> >> This change introduces the behaviour described above by scanning the
> >> entire scsi target when LUN is set to 0. This is both a functional and a
> >> performance fix. It aligns the driver with the spec and allows control
> >> planes to hotplug targets with large numbers of LUNs without having to
> >> request a RESCAN for each one of them.
> >> 
> >> Signed-off-by: Matej Genci <matej@nutanix.com>
> >> Suggested-by: Felipe Franciosi <felipe@nutanix.com>
> >> ---
> >> drivers/scsi/virtio_scsi.c | 7 ++++++-
> >> 1 file changed, 6 insertions(+), 1 deletion(-)
> >> 
> >> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
> >> index bfec84aacd90..a4b9bc7b4b4a 100644
> >> --- a/drivers/scsi/virtio_scsi.c
> >> +++ b/drivers/scsi/virtio_scsi.c
> >> @@ -284,7 +284,12 @@ static void virtscsi_handle_transport_reset(struct virtio_scsi *vscsi,
> >> 
> >> 	switch (virtio32_to_cpu(vscsi->vdev, event->reason)) {
> >> 	case VIRTIO_SCSI_EVT_RESET_RESCAN:
> >> -		scsi_add_device(shost, 0, target, lun);
> >> +		if (lun == 0) {
> >> +			scsi_scan_target(&shost->shost_gendev, 0, target,
> >> +					 SCAN_WILD_CARD, SCSI_SCAN_INITIAL);
> >> +		} else {
> >> +			scsi_add_device(shost, 0, target, lun);
> >> +		}
> >> 		break;
> >> 	case VIRTIO_SCSI_EVT_RESET_REMOVED:
> >> 		sdev = scsi_device_lookup(shost, 0, target, lun);
> >> 
> > 
> > 
> > Acked-by: Paolo Bonzini <pbonzini@redhat.com>
> 
> Cc: stable@vger.kernel.org
> 
> Thanks, Paolo.
> 
> I'm Cc'ing stable as I believe this fixes a driver bug where it
> doesn't follow the spec. Per commit message, today devices are
> required to issue RESCAN events for each LUN behind a target when
> hotplugging, or risking the driver not seeing the new LUNs.
> 
> Is this enough? Or should we resend after merge per below?
> https://www.kernel.org/doc/Documentation/process/stable-kernel-rules.rst

You need to let stable know the git commit id of the patch in Linus's
tree if the cc: stable is not on the final commit that gets merged.

thanks,

greg k-h

Re: [PATCH] Rescan the entire target on transport reset when LUN is 0

[Martin K. Petersen]

Matej,

> This change introduces the behaviour described above by scanning the
> entire scsi target when LUN is set to 0. This is both a functional and a
> performance fix. It aligns the driver with the spec and allows control
> planes to hotplug targets with large numbers of LUNs without having to
> request a RESCAN for each one of them.

Applied to 5.10/scsi-staging, thanks!

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: [PATCH] Rescan the entire target on transport reset when LUN is 0

[Martin K. Petersen]

On Fri, 28 Aug 2020 12:21:35 +0000, Matej Genci wrote:

> VirtIO 1.0 spec says
>     The removed and rescan events ... when sent for LUN 0, they MAY
>     apply to the entire target so the driver can ask the initiator
>     to rescan the target to detect this.
> 
> This change introduces the behaviour described above by scanning the
> entire scsi target when LUN is set to 0. This is both a functional and a
> performance fix. It aligns the driver with the spec and allows control
> planes to hotplug targets with large numbers of LUNs without having to
> request a RESCAN for each one of them.

Applied to 5.10/scsi-queue, thanks!

[1/1] scsi: virtio_scsi: Rescan the entire target on transport reset when LUN is 0
      https://git.kernel.org/mkp/scsi/c/beef6fd02b90

-- 
Martin K. Petersen	Oracle Linux Engineering