Critical fix:

- Fixes hang on HEAD OF QUEUE commands under high load


git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@333 d57e44dd-8a1f-0410-8b47-8ef2f437770f

scst/include/scsi_tgt.h

@@ -1082,9 +1082,12 @@ struct scst_cmd
 	 */
 	unsigned int preprocessing_only:1;
 
-	/* Set if scst_cmd_set_sn() was called */
+	/* Set if cmd's SN was set */
 	unsigned int sn_set:1;
 
+	/* Set if hq_cmd_count was incremented */
+	unsigned int hq_cmd_inced:1;
+
 	/*
 	 * Set if scst_cmd_init_stage1_done() called and the target wants
 	 * that the SN for the cmd won't be assigned until scst_restart_cmd()

scst/src/scst_lib.c

@@ -3045,6 +3045,9 @@ void scst_on_hq_cmd_response(struct scst_cmd *cmd)
 
 	TRACE_ENTRY();
 
+	if (!cmd->hq_cmd_inced)
+		goto out;
+
 	spin_lock_irq(&tgt_dev->sn_lock);
 	tgt_dev->hq_cmd_count--;
 	spin_unlock_irq(&tgt_dev->sn_lock);
@@ -3059,6 +3062,7 @@ void scst_on_hq_cmd_response(struct scst_cmd *cmd)
 	if (tgt_dev->hq_cmd_count == 0)
 		scst_make_deferred_commands_active(tgt_dev, cmd);
 
+out:
 	TRACE_EXIT();
 	return;
 }

scst/src/scst_targ.c

@@ -2725,11 +2725,15 @@ static void scst_cmd_set_sn(struct scst_cmd *cmd)
 	struct scst_tgt_dev *tgt_dev = cmd->tgt_dev;
 	unsigned long flags;
 
+	TRACE_ENTRY();
+
 	if (scst_is_implicit_hq(cmd)) {
 		TRACE(TRACE_SCSI|TRACE_SCSI_SERIALIZING, "Implicit HQ cmd %p", cmd);
 		cmd->queue_type = SCST_CMD_QUEUE_HEAD_OF_QUEUE;
 	}
 
+	EXTRACHECKS_BUG_ON(cmd->sn_set || cmd->hq_cmd_inced);
+
 	/* Optimized for lockless fast path */
 
 	scst_check_debug_sn(cmd);
@@ -2817,6 +2821,7 @@ ordered:
 		spin_lock_irqsave(&tgt_dev->sn_lock, flags);
 		tgt_dev->hq_cmd_count++;
 		spin_unlock_irqrestore(&tgt_dev->sn_lock, flags);
+		cmd->hq_cmd_inced = 1;
 		goto out;
 
 	default:
@@ -2833,6 +2838,7 @@ ordered:
 	cmd->sn_set = 1;
 
 out:
+	TRACE_EXIT();
 	return;
 }