On 9/13/21 1:53 AM, Adrian Hunter wrote:

scsi_dec_host_busy() is called for any non-zero return value like
SCSI_MLQUEUE_HOST_BUSY:

i.e.
	reason = scsi_dispatch_cmd(cmd);
	if (reason) {
		scsi_set_blocked(cmd, reason);
		ret = BLK_STS_RESOURCE;
		goto out_dec_host_busy;
	}

	return BLK_STS_OK;

out_dec_host_busy:
	scsi_dec_host_busy(shost, cmd);

And that will wake the error handler:

static void scsi_dec_host_busy(struct Scsi_Host *shost, struct scsi_cmnd *cmd)
{
	unsigned long flags;

	rcu_read_lock();
	__clear_bit(SCMD_STATE_INFLIGHT, &cmd->state);
	if (unlikely(scsi_host_in_recovery(shost))) {
		spin_lock_irqsave(shost->host_lock, flags);
		if (shost->host_failed || shost->host_eh_scheduled)
			scsi_eh_wakeup(shost);
		spin_unlock_irqrestore(shost->host_lock, flags);
	}
	rcu_read_unlock();
}

Returning SCSI_MLQUEUE_HOST_BUSY is not sufficient to wake up the SCSI
error handler because of the following test in scsi_error_handler():

	shost->host_failed != scsi_host_busy(shost)

As I mentioned in a previous email, all pending commands must have failed
or timed out before the error handler is woken up. Returning
SCSI_MLQUEUE_HOST_BUSY from ufshcd_queuecommand() does not fail a command
and prevents it from timing out. Hence my suggestion to change
"return SCSI_MLQUEUE_HOST_BUSY" into set_host_byte(cmd, DID_IMM_RETRY)
followed by cmd->scsi_done(cmd). A possible alternative is to move the
blk_mq_start_request() call in the SCSI core such that the block layer
request timer is not reset if a SCSI LLD returns SCSI_MLQUEUE_HOST_BUSY.

Bart.