On 2020-08-28 18:12, Alan Stern wrote:

On Fri, Aug 28, 2020 at 05:51:03PM -0700, Bart Van Assche wrote:

...

On 2020-08-28 08:37, Alan Stern wrote:

...

There may be an even simpler solution: Ensure that SCSI domain validation is mutually exclusive with runtime PM. It's already mutually exclusive with system PM, so this makes sense.

What do you think of the patch below?

Alan Stern

Index: usb-devel/drivers/scsi/scsi_transport_spi.c

--- usb-devel.orig/drivers/scsi/scsi_transport_spi.c +++ usb-devel/drivers/scsi/scsi_transport_spi.c @@ -1001,7 +1001,7 @@ spi_dv_device(struct scsi_device *sdev) * Because this function and the power management code both call * scsi_device_quiesce(), it is not safe to perform domain validation * while suspend or resume is in progress. Hence the

• * lock/unlock_system_sleep() calls.
  

• * lock/unlock_system_sleep() and scsi_autopm_get/put_device() calls.
  

  */ lock_system_sleep();

@@ -1018,10 +1018,13 @@ spi_dv_device(struct scsi_device *sdev) if (unlikely(!buffer)) goto out_put;

• if (scsi_autopm_get_device(sdev))

• goto out_free;
  

• /* We need to verify that the actual device will quiesce; the
  • later target quiesce is just a nice to have */
  if (unlikely(scsi_device_quiesce(sdev)))

• goto out_free;
  

• goto out_autopm_put;
  

scsi_target_quiesce(starget); @@ -1041,6 +1044,8 @@ spi_dv_device(struct scsi_device *sdev) spi_initial_dv(starget) = 1;

• out_autopm_put:
• scsi_autopm_put_device(sdev); out_free: kfree(buffer); out_put:

Hi Alan,

I think this is only a part of the solution. scsi_target_quiesce() invokes scsi_device_quiesce() and that function in turn calls blk_set_pm_only(). So I think that the above is not sufficient to fix the deadlock mentioned in my previous email.

Sorry, it sounds like you misinterpreted my preceding email. I meant to suggest that the patch above should be considered _instead of_ the patch that introduced BLK_MQ_REQ_PM. So blk_queue_enter() would remain unchanged, using the BLK_MQ_REQ_PREEMPT flag to decide whether or not to postpone new requests. Thus the deadlock you're concerned about would not arise.

Hi Alan,

Thanks for the clarification. I agree that the above patch should serialize SCSI DV and runtime PM. I'm fine with the above patch.

Thanks,

Bart.