[PATCH v2] scsi_debug: add new defer_type for mq_poll

[Douglas Gilbert <dgilbert@interlog.com>]

Add a new sdeb_defer_type enumeration: SDEB_DEFER_POLL for requests
that have REQ_HIPRI set in cmd_flags field. It is expected that
these requests will be polled via the mq_poll entry point which
is driven by calls to blk_poll() in the block layer. Therefore
timer events are not 'wired up' in the normal fashion.

There are still cases with short delays (e.g. < 10 microseconds)
where by the time the command reponse processing occurs, the delay
is already exceeded in which case the code calls scsi_done()
directly. In such cases there is no window for mq_poll() to be
called.

Add 'mq_polls' counter that increments on each scsi_done() called
via the mq_poll entry point. Can be used to show (with 'cat
/proc/scsi/scsi_debug/<host_id>') that blk_poll() is causing
completions rather than some of mechanism.


This patch is against the 5.12/scsi-staging branch which includes
   a98d6bdf181eb71bf4686666eaf47c642a061642
   scsi_debug : iouring iopoll support
which it alters. So this patch is a fix of that patch.

Changes since version 1 [sent 20210201 to linux-scsi list]
  - harden SDEB_DEFER_POLL which broke under testing
  - add mq_polls counter for debug output

Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
---
 drivers/scsi/scsi_debug.c | 137 +++++++++++++++++++++++++-------------
 1 file changed, 90 insertions(+), 47 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 746eec521f79..f46e8b3811f5 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -322,17 +322,19 @@ struct sdeb_store_info {
 	container_of(d, struct sdebug_host_info, dev)
 
 enum sdeb_defer_type {SDEB_DEFER_NONE = 0, SDEB_DEFER_HRT = 1,
-		      SDEB_DEFER_WQ = 2};
+		      SDEB_DEFER_WQ = 2, SDEB_DEFER_POLL = 3};
 
 struct sdebug_defer {
 	struct hrtimer hrt;
 	struct execute_work ew;
+	ktime_t cmpl_ts;/* time since boot to complete this cmd */
 	int sqa_idx;	/* index of sdebug_queue array */
 	int qc_idx;	/* index of sdebug_queued_cmd array within sqa_idx */
 	int hc_idx;	/* hostwide tag index */
 	int issuing_cpu;
 	bool init_hrt;
 	bool init_wq;
+	bool init_poll;
 	bool aborted;	/* true when blk_abort_request() already called */
 	enum sdeb_defer_type defer_t;
 };
@@ -357,6 +359,7 @@ static atomic_t sdebug_completions;  /* count of deferred completions */
 static atomic_t sdebug_miss_cpus;    /* submission + completion cpus differ */
 static atomic_t sdebug_a_tsf;	     /* 'almost task set full' counter */
 static atomic_t sdeb_inject_pending;
+static atomic_t sdeb_mq_poll_count;  /* bumped when mq_poll returns > 0 */
 
 struct opcode_info_t {
 	u8 num_attached;	/* 0 if this is it (i.e. a leaf); use 0xff */
@@ -4730,7 +4733,6 @@ static void sdebug_q_cmd_complete(struct sdebug_defer *sd_dp)
 	struct scsi_cmnd *scp;
 	struct sdebug_dev_info *devip;
 
-	sd_dp->defer_t = SDEB_DEFER_NONE;
 	if (unlikely(aborted))
 		sd_dp->aborted = false;
 	qc_idx = sd_dp->qc_idx;
@@ -4745,6 +4747,7 @@ static void sdebug_q_cmd_complete(struct sdebug_defer *sd_dp)
 		return;
 	}
 	spin_lock_irqsave(&sqp->qc_lock, iflags);
+	sd_dp->defer_t = SDEB_DEFER_NONE;
 	sqcp = &sqp->qc_arr[qc_idx];
 	scp = sqcp->a_cmnd;
 	if (unlikely(scp == NULL)) {
@@ -5517,40 +5520,66 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 				kt -= d;
 			}
 		}
-		if (!sd_dp->init_hrt) {
-			sd_dp->init_hrt = true;
-			sqcp->sd_dp = sd_dp;
-			hrtimer_init(&sd_dp->hrt, CLOCK_MONOTONIC,
-				     HRTIMER_MODE_REL_PINNED);
-			sd_dp->hrt.function = sdebug_q_cmd_hrt_complete;
-			sd_dp->sqa_idx = sqp - sdebug_q_arr;
-			sd_dp->qc_idx = k;
+		sd_dp->cmpl_ts = ktime_add(ns_to_ktime(ns_from_boot), kt);
+		if (cmnd->request->cmd_flags & REQ_HIPRI) {
+			spin_lock_irqsave(&sqp->qc_lock, iflags);
+			if (!sd_dp->init_poll) {
+				sd_dp->init_poll = true;
+				sqcp->sd_dp = sd_dp;
+				sd_dp->sqa_idx = sqp - sdebug_q_arr;
+				sd_dp->qc_idx = k;
+			}
+			sd_dp->defer_t = SDEB_DEFER_POLL;
+			spin_unlock_irqrestore(&sqp->qc_lock, iflags);
+		} else {
+			if (!sd_dp->init_hrt) {
+				sd_dp->init_hrt = true;
+				sqcp->sd_dp = sd_dp;
+				hrtimer_init(&sd_dp->hrt, CLOCK_MONOTONIC,
+					     HRTIMER_MODE_REL_PINNED);
+				sd_dp->hrt.function = sdebug_q_cmd_hrt_complete;
+				sd_dp->sqa_idx = sqp - sdebug_q_arr;
+				sd_dp->qc_idx = k;
+			}
+			sd_dp->defer_t = SDEB_DEFER_HRT;
+			/* schedule the invocation of scsi_done() for a later time */
+			hrtimer_start(&sd_dp->hrt, kt, HRTIMER_MODE_REL_PINNED);
 		}
 		if (sdebug_statistics)
 			sd_dp->issuing_cpu = raw_smp_processor_id();
-		sd_dp->defer_t = SDEB_DEFER_HRT;
-		/* schedule the invocation of scsi_done() for a later time */
-		hrtimer_start(&sd_dp->hrt, kt, HRTIMER_MODE_REL_PINNED);
 	} else {	/* jdelay < 0, use work queue */
-		if (!sd_dp->init_wq) {
-			sd_dp->init_wq = true;
-			sqcp->sd_dp = sd_dp;
-			sd_dp->sqa_idx = sqp - sdebug_q_arr;
-			sd_dp->qc_idx = k;
-			INIT_WORK(&sd_dp->ew.work, sdebug_q_cmd_wq_complete);
-		}
-		if (sdebug_statistics)
-			sd_dp->issuing_cpu = raw_smp_processor_id();
-		sd_dp->defer_t = SDEB_DEFER_WQ;
 		if (unlikely((sdebug_opts & SDEBUG_OPT_CMD_ABORT) &&
 			     atomic_read(&sdeb_inject_pending)))
 			sd_dp->aborted = true;
-		schedule_work(&sd_dp->ew.work);
-		if (unlikely((sdebug_opts & SDEBUG_OPT_CMD_ABORT) &&
-			     atomic_read(&sdeb_inject_pending))) {
+		sd_dp->cmpl_ts = ns_to_ktime(ns_from_boot);
+		if (cmnd->request->cmd_flags & REQ_HIPRI) {
+			spin_lock_irqsave(&sqp->qc_lock, iflags);
+			if (!sd_dp->init_poll) {
+				sd_dp->init_poll = true;
+				sqcp->sd_dp = sd_dp;
+				sd_dp->sqa_idx = sqp - sdebug_q_arr;
+				sd_dp->qc_idx = k;
+			}
+			sd_dp->defer_t = SDEB_DEFER_POLL;
+			spin_unlock_irqrestore(&sqp->qc_lock, iflags);
+		} else {
+			if (!sd_dp->init_wq) {
+				sd_dp->init_wq = true;
+				sqcp->sd_dp = sd_dp;
+				sd_dp->sqa_idx = sqp - sdebug_q_arr;
+				sd_dp->qc_idx = k;
+				INIT_WORK(&sd_dp->ew.work, sdebug_q_cmd_wq_complete);
+			}
+			sd_dp->defer_t = SDEB_DEFER_WQ;
+			schedule_work(&sd_dp->ew.work);
+		}
+		if (sdebug_statistics)
+			sd_dp->issuing_cpu = raw_smp_processor_id();
+		if (unlikely(sd_dp->aborted)) {
 			sdev_printk(KERN_INFO, sdp, "abort request tag %d\n", cmnd->request->tag);
 			blk_abort_request(cmnd->request);
 			atomic_set(&sdeb_inject_pending, 0);
+			sd_dp->aborted = false;
 		}
 	}
 	if (unlikely((SDEBUG_OPT_Q_NOISE & sdebug_opts) && scsi_result == device_qfull_result))
@@ -5779,11 +5808,12 @@ static int scsi_debug_show_info(struct seq_file *m, struct Scsi_Host *host)
 		   dix_reads, dix_writes, dif_errors);
 	seq_printf(m, "usec_in_jiffy=%lu, statistics=%d\n", TICK_NSEC / 1000,
 		   sdebug_statistics);
-	seq_printf(m, "cmnd_count=%d, completions=%d, %s=%d, a_tsf=%d\n",
+	seq_printf(m, "cmnd_count=%d, completions=%d, %s=%d, a_tsf=%d, mq_polls=%d\n",
 		   atomic_read(&sdebug_cmnd_count),
 		   atomic_read(&sdebug_completions),
 		   "miss_cpus", atomic_read(&sdebug_miss_cpus),
-		   atomic_read(&sdebug_a_tsf));
+		   atomic_read(&sdebug_a_tsf),
+		   atomic_read(&sdeb_mq_poll_count));
 
 	seq_printf(m, "submit_queues=%d\n", submit_queues);
 	for (j = 0, sqp = sdebug_q_arr; j < submit_queues; ++j, ++sqp) {
@@ -7246,52 +7276,64 @@ static int sdebug_map_queues(struct Scsi_Host *shost)
 
 static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 {
-	int qc_idx;
-	int retiring = 0;
+	bool first;
+	bool retiring = false;
+	int num_entries = 0;
+	unsigned int qc_idx = 0;
 	unsigned long iflags;
+	ktime_t kt_from_boot = ktime_get_boottime();
 	struct sdebug_queue *sqp;
 	struct sdebug_queued_cmd *sqcp;
 	struct scsi_cmnd *scp;
 	struct sdebug_dev_info *devip;
-	int num_entries = 0;
 
 	sqp = sdebug_q_arr + queue_num;
+	spin_lock_irqsave(&sqp->qc_lock, iflags);
 
-	do {
-		spin_lock_irqsave(&sqp->qc_lock, iflags);
-		qc_idx = find_first_bit(sqp->in_use_bm, sdebug_max_queue);
-		if (unlikely((qc_idx < 0) || (qc_idx >= sdebug_max_queue)))
-			goto out;
+	for (first = true; first || qc_idx + 1 < sdebug_max_queue; )   {
+		if (first) {
+			qc_idx = find_first_bit(sqp->in_use_bm, sdebug_max_queue);
+			first = false;
+		} else {
+			qc_idx = find_next_bit(sqp->in_use_bm, sdebug_max_queue, qc_idx + 1);
+		}
+		if (unlikely(qc_idx >= sdebug_max_queue))
+			break;
 
 		sqcp = &sqp->qc_arr[qc_idx];
 		scp = sqcp->a_cmnd;
 		if (unlikely(scp == NULL)) {
-			pr_err("scp is NULL, queue_num=%d, qc_idx=%d from %s\n",
+			pr_err("scp is NULL, queue_num=%d, qc_idx=%u from %s\n",
 			       queue_num, qc_idx, __func__);
-			goto out;
+			break;
 		}
+		if (sqcp->sd_dp->defer_t == SDEB_DEFER_POLL) {
+			if (kt_from_boot < sqcp->sd_dp->cmpl_ts)
+				continue;
+
+		} else		/* ignoring non REQ_HIPRI requests */
+			continue;
 		devip = (struct sdebug_dev_info *)scp->device->hostdata;
 		if (likely(devip))
 			atomic_dec(&devip->num_in_q);
 		else
 			pr_err("devip=NULL from %s\n", __func__);
 		if (unlikely(atomic_read(&retired_max_queue) > 0))
-			retiring = 1;
+			retiring = true;
 
 		sqcp->a_cmnd = NULL;
 		if (unlikely(!test_and_clear_bit(qc_idx, sqp->in_use_bm))) {
-			pr_err("Unexpected completion sqp %p queue_num=%d qc_idx=%d from %s\n",
+			pr_err("Unexpected completion sqp %p queue_num=%d qc_idx=%u from %s\n",
 				sqp, queue_num, qc_idx, __func__);
-			goto out;
+			break;
 		}
-
 		if (unlikely(retiring)) {	/* user has reduced max_queue */
 			int k, retval;
 
 			retval = atomic_read(&retired_max_queue);
 			if (qc_idx >= retval) {
 				pr_err("index %d too large\n", retval);
-				goto out;
+				break;
 			}
 			k = find_last_bit(sqp->in_use_bm, retval);
 			if ((k < sdebug_max_queue) || (k == retval))
@@ -7299,17 +7341,18 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 			else
 				atomic_set(&retired_max_queue, k + 1);
 		}
+		sqcp->sd_dp->defer_t = SDEB_DEFER_NONE;
 		spin_unlock_irqrestore(&sqp->qc_lock, iflags);
 		scp->scsi_done(scp); /* callback to mid level */
+		spin_lock_irqsave(&sqp->qc_lock, iflags);
 		num_entries++;
-	} while (1);
-
-out:
+	}
 	spin_unlock_irqrestore(&sqp->qc_lock, iflags);
+	if (num_entries > 0)
+		atomic_add(num_entries, &sdeb_mq_poll_count);
 	return num_entries;
 }
 
-
 static int scsi_debug_queuecommand(struct Scsi_Host *shost,
 				   struct scsi_cmnd *scp)
 {
-- 
2.25.1