scsi: scsi_debug: Fix qc_lock use in sdebug_blk_mq_poll()

The use of the 'locked' boolean variable to control locking and unlocking
of the qc_lock spinlock of struct sdebug_queue confuses sparse, leading to
a warning about an unexpected unlock. Simplify the qc_lock lock/unlock
handling code of this function to avoid this warning by removing the
'locked' boolean variable. This change also fixes unlocked access to the
in_use_bm bitmap with the find_first_bit() function.

Link: https://lore.kernel.org/r/20220301113009.595857-3-damien.lemoal@opensource.wdc.com
Fixes: b05d4e48 ("scsi: scsi_debug: Refine sdebug_blk_mq_poll()")
Cc: stable@vger.kernel.org
Signed-off-by: NDamien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/scsi_debug.c

@@ -7509,7 +7509,6 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 {
 	bool first;
 	bool retiring = false;
-	bool locked = false;
 	int num_entries = 0;
 	unsigned int qc_idx = 0;
 	unsigned long iflags;
@@ -7525,11 +7524,9 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 	if (qc_idx >= sdebug_max_queue)
 		return 0;
 
+	spin_lock_irqsave(&sqp->qc_lock, iflags);
+
 	for (first = true; first || qc_idx + 1 < sdebug_max_queue; )   {
-		if (!locked) {
-			spin_lock_irqsave(&sqp->qc_lock, iflags);
-			locked = true;
-		}
 		if (first) {
 			first = false;
 			if (!test_bit(qc_idx, sqp->in_use_bm))
@@ -7586,14 +7583,15 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 		}
 		WRITE_ONCE(sd_dp->defer_t, SDEB_DEFER_NONE);
 		spin_unlock_irqrestore(&sqp->qc_lock, iflags);
-		locked = false;
 		scsi_done(scp); /* callback to mid level */
 		num_entries++;
+		spin_lock_irqsave(&sqp->qc_lock, iflags);
 		if (find_first_bit(sqp->in_use_bm, sdebug_max_queue) >= sdebug_max_queue)
-			break;	/* if no more then exit without retaking spinlock */
+			break;
 	}
-	if (locked)
-		spin_unlock_irqrestore(&sqp->qc_lock, iflags);
+
+	spin_unlock_irqrestore(&sqp->qc_lock, iflags);
+
 	if (num_entries > 0)
 		atomic_add(num_entries, &sdeb_mq_poll_count);
 	return num_entries;