From:   John Garry <john.g.garry@oracle.com>
To:     jejb@linux.ibm.com, martin.petersen@oracle.com
Cc:     linux-scsi@vger.kernel.org, bvanassche@acm.org,
        linux-kernel@vger.kernel.org, dgilbert@interlog.com,
        John Garry <john.g.garry@oracle.com>
Subject: [PATCH RESEND v2 09/11] scsi: scsi_debug: Drop sdebug_dev_info.num_in_q
Date:   Mon, 13 Mar 2023 09:31:12 +0000
Message-Id: <20230313093114.1498305-10-john.g.garry@oracle.com>
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In schedule_resp(), under certain conditions we check whether the
per-device queue is full (num_in_q == queue depth - 1) and we may inject a
"task set full" (TSF) error if it is.

However how we read num_in_q is racy - many threads may see the same
"queue is full" value (and also issue a TSF).

There is per-queue locking in reading per-device num_in_q, but that would
not help.

Replace how we read num_in_q at this location with a call to
scsi_device_busy(). Calling scsi_device_busy() is likewise racy (as reading
num_in_q), so nothing lost or gained. Calling scsi_device_busy() is also
slow as it needs to read all bits in the per-device budget bitmap, but we
can live with that since we're just a simulator and it's only under
a certain configs which we would see this.

Also move the "task set full" print earlier as it would only be called
now under this condition. However, previously it may not have been
called - like returning early - but keep it simple and always call it.

At this point we can drop sdebug_dev_info.num_in_q - it is difficult to
maintain properly and adds extra normal case command processing.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 drivers/scsi/scsi_debug.c | 63 ++++++++++-----------------------------
 1 file changed, 16 insertions(+), 47 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 0d515bac93bf..449b460e4c1b 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -288,7 +288,6 @@ struct sdebug_dev_info {
 	uuid_t lu_name;
 	struct sdebug_host_info *sdbg_host;
 	unsigned long uas_bm[1];
-	atomic_t num_in_q;
 	atomic_t stopped;	/* 1: by SSU, 2: device start */
 	bool used;
 
@@ -4931,7 +4930,6 @@ static void sdebug_q_cmd_complete(struct sdebug_defer *sd_dp)
 	struct sdebug_queue *sqp;
 	struct sdebug_queued_cmd *sqcp;
 	struct scsi_cmnd *scp;
-	struct sdebug_dev_info *devip;
 
 	if (unlikely(aborted))
 		sd_dp->aborted = false;
@@ -4956,11 +4954,7 @@ static void sdebug_q_cmd_complete(struct sdebug_defer *sd_dp)
 		       sd_dp->sqa_idx, qc_idx, sd_dp->hc_idx);
 		return;
 	}
-	devip = (struct sdebug_dev_info *)scp->device->hostdata;
-	if (likely(devip))
-		atomic_dec(&devip->num_in_q);
-	else
-		pr_err("devip=NULL\n");
+
 	if (unlikely(atomic_read(&retired_max_queue) > 0))
 		retiring = 1;
 
@@ -5192,7 +5186,6 @@ static struct sdebug_dev_info *find_build_dev_info(struct scsi_device *sdev)
 	open_devip->target = sdev->id;
 	open_devip->lun = sdev->lun;
 	open_devip->sdbg_host = sdbg_host;
-	atomic_set(&open_devip->num_in_q, 0);
 	set_bit(SDEBUG_UA_POOCCUR, open_devip->uas_bm);
 	open_devip->used = true;
 	return open_devip;
@@ -5263,7 +5256,6 @@ static bool stop_queued_cmnd(struct scsi_cmnd *cmnd)
 	enum sdeb_defer_type l_defer_t;
 	struct sdebug_queue *sqp;
 	struct sdebug_queued_cmd *sqcp;
-	struct sdebug_dev_info *devip;
 	struct sdebug_defer *sd_dp;
 
 	for (j = 0, sqp = sdebug_q_arr; j < submit_queues; ++j, ++sqp) {
@@ -5278,10 +5270,6 @@ static bool stop_queued_cmnd(struct scsi_cmnd *cmnd)
 				if (cmnd != sqcp->a_cmnd)
 					continue;
 				/* found */
-				devip = (struct sdebug_dev_info *)
-						cmnd->device->hostdata;
-				if (devip)
-					atomic_dec(&devip->num_in_q);
 				sqcp->a_cmnd = NULL;
 				sd_dp = sqcp->sd_dp;
 				if (sd_dp) {
@@ -5308,7 +5296,6 @@ static void stop_all_queued(void)
 	enum sdeb_defer_type l_defer_t;
 	struct sdebug_queue *sqp;
 	struct sdebug_queued_cmd *sqcp;
-	struct sdebug_dev_info *devip;
 	struct sdebug_defer *sd_dp;
 
 	for (j = 0, sqp = sdebug_q_arr; j < submit_queues; ++j, ++sqp) {
@@ -5318,10 +5305,6 @@ static void stop_all_queued(void)
 				sqcp = &sqp->qc_arr[k];
 				if (sqcp->a_cmnd == NULL)
 					continue;
-				devip = (struct sdebug_dev_info *)
-					sqcp->a_cmnd->device->hostdata;
-				if (devip)
-					atomic_dec(&devip->num_in_q);
 				sqcp->a_cmnd = NULL;
 				sd_dp = sqcp->sd_dp;
 				if (sd_dp) {
@@ -5565,9 +5548,8 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 			 int delta_jiff, int ndelay)
 {
 	bool new_sd_dp;
-	bool inject = false;
 	bool polled = scsi_cmd_to_rq(cmnd)->cmd_flags & REQ_POLLED;
-	int k, num_in_q, qdepth;
+	int k;
 	unsigned long iflags;
 	u64 ns_from_boot = 0;
 	struct sdebug_queue *sqp;
@@ -5591,16 +5573,21 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 		spin_unlock_irqrestore(&sqp->qc_lock, iflags);
 		return SCSI_MLQUEUE_HOST_BUSY;
 	}
-	num_in_q = atomic_read(&devip->num_in_q);
-	qdepth = cmnd->device->queue_depth;
+
 	if (unlikely(sdebug_every_nth && (SDEBUG_OPT_RARE_TSF & sdebug_opts) &&
 		     (scsi_result == 0))) {
+		int num_in_q = scsi_device_busy(sdp);
+		int qdepth = cmnd->device->queue_depth;
+
 		if ((num_in_q == (qdepth - 1)) &&
 		    (atomic_inc_return(&sdebug_a_tsf) >=
 		     abs(sdebug_every_nth))) {
 			atomic_set(&sdebug_a_tsf, 0);
-			inject = true;
 			scsi_result = device_qfull_result;
+
+			if (unlikely(SDEBUG_OPT_Q_NOISE & sdebug_opts))
+				sdev_printk(KERN_INFO, sdp, "%s: num_in_q=%d +1, <inject> status: TASK SET FULL\n",
+					    __func__, num_in_q);
 		}
 	}
 
@@ -5616,7 +5603,6 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 		goto respond_in_thread;
 	}
 	set_bit(k, sqp->in_use_bm);
-	atomic_inc(&devip->num_in_q);
 	sqcp = &sqp->qc_arr[k];
 	sqcp->a_cmnd = cmnd;
 	cmnd->host_scribble = (unsigned char *)sqcp;
@@ -5626,7 +5612,6 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 	if (!sd_dp) {
 		sd_dp = kzalloc(sizeof(*sd_dp), GFP_ATOMIC);
 		if (!sd_dp) {
-			atomic_dec(&devip->num_in_q);
 			clear_bit(k, sqp->in_use_bm);
 			return SCSI_MLQUEUE_HOST_BUSY;
 		}
@@ -5686,7 +5671,6 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 				if (kt <= d) {	/* elapsed duration >= kt */
 					spin_lock_irqsave(&sqp->qc_lock, iflags);
 					sqcp->a_cmnd = NULL;
-					atomic_dec(&devip->num_in_q);
 					clear_bit(k, sqp->in_use_bm);
 					spin_unlock_irqrestore(&sqp->qc_lock, iflags);
 					if (new_sd_dp)
@@ -5762,9 +5746,7 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 			sd_dp->aborted = false;
 		}
 	}
-	if (unlikely((SDEBUG_OPT_Q_NOISE & sdebug_opts) && scsi_result == device_qfull_result))
-		sdev_printk(KERN_INFO, sdp, "%s: num_in_q=%d +1, %s%s\n", __func__,
-			    num_in_q, (inject ? "<inject> " : ""), "status: TASK SET FULL");
+
 	return 0;
 
 respond_in_thread:	/* call back to mid-layer using invocation thread */
@@ -7369,17 +7351,12 @@ static void sdebug_do_remove_host(bool the_end)
 
 static int sdebug_change_qdepth(struct scsi_device *sdev, int qdepth)
 {
-	int num_in_q = 0;
-	struct sdebug_dev_info *devip;
+	struct sdebug_dev_info *devip = sdev->hostdata;
 
-	block_unblock_all_queues(true);
-	devip = (struct sdebug_dev_info *)sdev->hostdata;
-	if (NULL == devip) {
-		block_unblock_all_queues(false);
+	if (!devip)
 		return	-ENODEV;
-	}
-	num_in_q = atomic_read(&devip->num_in_q);
 
+	block_unblock_all_queues(true);
 	if (qdepth > SDEBUG_CANQUEUE) {
 		qdepth = SDEBUG_CANQUEUE;
 		pr_warn("%s: requested qdepth [%d] exceeds canqueue [%d], trim\n", __func__,
@@ -7390,10 +7367,8 @@ static int sdebug_change_qdepth(struct scsi_device *sdev, int qdepth)
 	if (qdepth != sdev->queue_depth)
 		scsi_change_queue_depth(sdev, qdepth);
 
-	if (SDEBUG_OPT_Q_NOISE & sdebug_opts) {
-		sdev_printk(KERN_INFO, sdev, "%s: qdepth=%d, num_in_q=%d\n",
-			    __func__, qdepth, num_in_q);
-	}
+	if (SDEBUG_OPT_Q_NOISE & sdebug_opts)
+		sdev_printk(KERN_INFO, sdev, "%s: qdepth=%d\n", __func__, qdepth);
 	block_unblock_all_queues(false);
 	return sdev->queue_depth;
 }
@@ -7495,7 +7470,6 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 	struct sdebug_queue *sqp;
 	struct sdebug_queued_cmd *sqcp;
 	struct scsi_cmnd *scp;
-	struct sdebug_dev_info *devip;
 	struct sdebug_defer *sd_dp;
 
 	sqp = sdebug_q_arr + queue_num;
@@ -7533,11 +7507,6 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 
 		} else		/* ignoring non REQ_POLLED 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 = true;
 
-- 
2.35.3