Re: [PATCH V3 1/3] scsi: ufs: Fix error handler clear ua deadlock

[Bart Van Assche <bvanassche@acm.org>]

On 9/7/21 9:56 AM, Bart Van Assche wrote:
> On 9/7/21 8:43 AM, Adrian Hunter wrote:
>> No.  Requests cannot make progress when ufshcd_state is
>> UFSHCD_STATE_EH_SCHEDULED_FATAL, and only the error handler can change 
>> that,
>> so if the error handler is waiting to enter the queue and 
>> blk_mq_freeze_queue()
>> is waiting for outstanding requests, they will deadlock.
> 
> How about adding the above text as a comment above 
> ufshcd_clear_ua_wluns() such
> that this information becomes available to those who have not followed this
> conversation?

After having given patch 1/3 some further thought: an unfortunate
effect of this patch is that unit attention clearing is skipped for
the states UFSHCD_STATE_EH_SCHEDULED_FATAL and UFSHCD_STATE_RESET.
How about replacing patch 1/3 with the untested patch below since that
patch does not have the disadvantage of sometimes skipping clearing UA?

Thanks,

Bart.

[PATCH] scsi: ufs: Fix a recently introduced deadlock

Completing pending commands with DID_IMM_RETRY triggers the following
code paths:

   scsi_complete()
   -> scsi_queue_insert()
     -> __scsi_queue_insert()
       -> scsi_device_unbusy()
         -> scsi_dec_host_busy()
	  -> scsi_eh_wakeup()
       -> blk_mq_requeue_request()

   scsi_queue_rq()
   -> scsi_host_queue_ready()
     -> scsi_host_in_recovery()

Fixes: a113eaaf8637 ("scsi: ufs: Synchronize SCSI and UFS error handling")
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
  drivers/scsi/ufs/ufshcd.c | 8 ++++++++
  1 file changed, 8 insertions(+)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index c2c614da1fb8..9560f34f3d27 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -2707,6 +2707,14 @@ static int ufshcd_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *cmd)
  		}
  		fallthrough;
  	case UFSHCD_STATE_RESET:
+		/*
+		 * The SCSI error handler only starts after all pending commands
+		 * have failed or timed out. Complete commands with
+		 * DID_IMM_RETRY to allow the error handler to start
+		 * if it has been scheduled.
+		 */
+		set_host_byte(cmd, DID_IMM_RETRY);
+		cmd->scsi_done(cmd);
  		err = SCSI_MLQUEUE_HOST_BUSY;
  		goto out;
  	case UFSHCD_STATE_ERROR: