s390/cio: avoid excessive path-verification requests

Currently when removing a device from cio_ignore list, we trigger a
path-verification for all the subchannels available in the system. This
could lead to path-verification requests on subchannels with an online
device, which could cause unwanted delay. Instead of all the
subchannels, trigger the path-verifications to those without an online
device.
Reported-by: Julian Wiedmann <jwi@linux.ibm.com>
Fixes: 2297791c ("s390/cio: dont unregister subchannel from child-drivers")
Signed-off-by: Vineeth Vijayan <vneethv@linux.ibm.com>
Reviewed-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

drivers/s390/cio/blacklist.c

@@ -262,10 +262,12 @@ static int blacklist_parse_proc_parameters(char *buf)
 
 	if (strcmp("free", parm) == 0) {
 		rc = blacklist_parse_parameters(buf, free, 0);
-		/* There could be subchannels without proper devices connected.
-		 * evaluate all the entries
+		/*
+		 * Evaluate the subchannels without an online device. This way,
+		 * no path-verification will be triggered on those subchannels
+		 * and it avoids unnecessary delays.
 		 */
-		css_schedule_eval_all();
+		css_schedule_eval_cond(CSS_EVAL_NOT_ONLINE, 0);
 	} else if (strcmp("add", parm) == 0)
 		rc = blacklist_parse_parameters(buf, add, 0);
 	else if (strcmp("purge", parm) == 0)

drivers/s390/cio/css.c

@@ -788,27 +788,49 @@ static int __unset_registered(struct device *dev, void *data)
 	return 0;
 }
 
-void css_schedule_eval_all_unreg(unsigned long delay)
+static int __unset_online(struct device *dev, void *data)
+{
+	struct idset *set = data;
+	struct subchannel *sch = to_subchannel(dev);
+	struct ccw_device *cdev = sch_get_cdev(sch);
+
+	if (cdev && cdev->online)
+		idset_sch_del(set, sch->schid);
+
+	return 0;
+}
+
+void css_schedule_eval_cond(enum css_eval_cond cond, unsigned long delay)
 {
 	unsigned long flags;
-	struct idset *unreg_set;
+	struct idset *set;
 
 	/* Find unregistered subchannels. */
-	unreg_set = idset_sch_new();
-	if (!unreg_set) {
+	set = idset_sch_new();
+	if (!set) {
 		/* Fallback. */
 		css_schedule_eval_all();
 		return;
 	}
-	idset_fill(unreg_set);
-	bus_for_each_dev(&css_bus_type, NULL, unreg_set, __unset_registered);
+	idset_fill(set);
+	switch (cond) {
+	case CSS_EVAL_UNREG:
+		bus_for_each_dev(&css_bus_type, NULL, set, __unset_registered);
+		break;
+	case CSS_EVAL_NOT_ONLINE:
+		bus_for_each_dev(&css_bus_type, NULL, set, __unset_online);
+		break;
+	default:
+		break;
+	}
+
 	/* Apply to slow_subchannel_set. */
 	spin_lock_irqsave(&slow_subchannel_lock, flags);
-	idset_add_set(slow_subchannel_set, unreg_set);
+	idset_add_set(slow_subchannel_set, set);
 	atomic_set(&css_eval_scheduled, 1);
 	queue_delayed_work(cio_work_q, &slow_path_work, delay);
 	spin_unlock_irqrestore(&slow_subchannel_lock, flags);
-	idset_free(unreg_set);
+	idset_free(set);
 }
 
 void css_wait_for_slow_path(void)
@@ -820,7 +842,7 @@ void css_wait_for_slow_path(void)
 void css_schedule_reprobe(void)
 {
 	/* Schedule with a delay to allow merging of subsequent calls. */
-	css_schedule_eval_all_unreg(1 * HZ);
+	css_schedule_eval_cond(CSS_EVAL_UNREG, 1 * HZ);
 }
 EXPORT_SYMBOL_GPL(css_schedule_reprobe);
 

drivers/s390/cio/css.h

@@ -34,6 +34,14 @@
 #define SNID_STATE3_MULTI_PATH	   1
 #define SNID_STATE3_SINGLE_PATH	   0
 
+/*
+ * Conditions used to specify which subchannels need evaluation
+ */
+enum css_eval_cond {
+	CSS_EVAL_UNREG,		/* unregistered subchannels */
+	CSS_EVAL_NOT_ONLINE	/* sch without an online-device */
+};
+
 struct path_state {
 	__u8  state1 : 2;	/* path state value 1 */
 	__u8  state2 : 2;	/* path state value 2 */
@@ -136,7 +144,7 @@ static inline struct channel_subsystem *css_by_id(u8 cssid)
 /* Helper functions to build lists for the slow path. */
 void css_schedule_eval(struct subchannel_id schid);
 void css_schedule_eval_all(void);
-void css_schedule_eval_all_unreg(unsigned long delay);
+void css_schedule_eval_cond(enum css_eval_cond, unsigned long delay);
 int css_complete_work(void);
 
 int sch_is_pseudo_sch(struct subchannel *);