s390/dasd: reorder lcu and device lock

Reorder lcu and device lock to get rid of the error-prone trylock
mechanism.

The locking order is lcu lock -> device lock.
This protects against changes to the lcu device lists and enables us
to iterate over the devices, take the cdev lock and make changes to
the device structures.

The complicated part is the summary unit check handler that gets an
interrupt on one device of the lcu that leads to structural changes of
the whole lcu itself. This work needs to be done even if devices on
the lcu disappear. So a device independent worker is used.
The old approach tried to update some lcu structures and set up the
lcu worker in the interrupt context with the device lock held.
But this forced the lock order "cdev lock -> lcu lock" that made it
hard to have the lcu lock held and iterate over all devices and change
them.

The new approach is to schedule a device specific worker that gets
out of the interrupt context and rid of the device lock for summary
unit checks. This worker is able to take the lcu lock and schedule the
lcu worker that updates all devices. The time between interrupt and
worker execution is no problem because the devices in the lcu reject
all I/O in this time with an appropriate error. The dasd driver can
deal with this situation and re-drive the I/O later on.

Signed-off-by: Stefan Haberland <sth@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 53 insertions, 173 deletions

diff --git a/drivers/s390/block/dasd_alias.c b/drivers/s390/block/dasd_alias.c
index 17ad5749e91d..1e560188dd13 100644
--- a/drivers/s390/block/dasd_alias.c
+++ b/drivers/s390/block/dasd_alias.c
@@ -317,17 +317,17 @@ static int _add_device_to_lcu(struct alias_lcu *lcu,
 	struct alias_pav_group *group;
 	struct dasd_uid uid;
 
+	spin_lock(get_ccwdev_lock(device->cdev));
 	private->uid.type = lcu->uac->unit[private->uid.real_unit_addr].ua_type;
 	private->uid.base_unit_addr =
 		lcu->uac->unit[private->uid.real_unit_addr].base_ua;
 	uid = private->uid;
-
+	spin_unlock(get_ccwdev_lock(device->cdev));
 	/* if we have no PAV anyway, we don't need to bother with PAV groups */
 	if (lcu->pav == NO_PAV) {
 		list_move(&device->alias_list, &lcu->active_devices);
 		return 0;
 	}
-
 	group = _find_group(lcu, &uid);
 	if (!group) {
 		group = kzalloc(sizeof(*group), GFP_ATOMIC);
@@ -397,130 +397,6 @@ suborder_not_supported(struct dasd_ccw_req *cqr)
 	return 0;
 }
 
-/*
- * This function tries to lock all devices on an lcu via trylock
- * return NULL on success otherwise return first failed device
- */
-static struct dasd_device *_trylock_all_devices_on_lcu(struct alias_lcu *lcu,
-						      struct dasd_device *pos)
-
-{
-	struct alias_pav_group *pavgroup;
-	struct dasd_device *device;
-
-	list_for_each_entry(device, &lcu->active_devices, alias_list) {
-		if (device == pos)
-			continue;
-		if (!spin_trylock(get_ccwdev_lock(device->cdev)))
-			return device;
-	}
-	list_for_each_entry(device, &lcu->inactive_devices, alias_list) {
-		if (device == pos)
-			continue;
-		if (!spin_trylock(get_ccwdev_lock(device->cdev)))
-			return device;
-	}
-	list_for_each_entry(pavgroup, &lcu->grouplist, group) {
-		list_for_each_entry(device, &pavgroup->baselist, alias_list) {
-			if (device == pos)
-				continue;
-			if (!spin_trylock(get_ccwdev_lock(device->cdev)))
-				return device;
-		}
-		list_for_each_entry(device, &pavgroup->aliaslist, alias_list) {
-			if (device == pos)
-				continue;
-			if (!spin_trylock(get_ccwdev_lock(device->cdev)))
-				return device;
-		}
-	}
-	return NULL;
-}
-
-/*
- * unlock all devices except the one that is specified as pos
- * stop if enddev is specified and reached
- */
-static void _unlock_all_devices_on_lcu(struct alias_lcu *lcu,
-				       struct dasd_device *pos,
-				       struct dasd_device *enddev)
-
-{
-	struct alias_pav_group *pavgroup;
-	struct dasd_device *device;
-
-	list_for_each_entry(device, &lcu->active_devices, alias_list) {
-		if (device == pos)
-			continue;
-		if (device == enddev)
-			return;
-		spin_unlock(get_ccwdev_lock(device->cdev));
-	}
-	list_for_each_entry(device, &lcu->inactive_devices, alias_list) {
-		if (device == pos)
-			continue;
-		if (device == enddev)
-			return;
-		spin_unlock(get_ccwdev_lock(device->cdev));
-	}
-	list_for_each_entry(pavgroup, &lcu->grouplist, group) {
-		list_for_each_entry(device, &pavgroup->baselist, alias_list) {
-			if (device == pos)
-				continue;
-			if (device == enddev)
-				return;
-			spin_unlock(get_ccwdev_lock(device->cdev));
-		}
-		list_for_each_entry(device, &pavgroup->aliaslist, alias_list) {
-			if (device == pos)
-				continue;
-			if (device == enddev)
-				return;
-			spin_unlock(get_ccwdev_lock(device->cdev));
-		}
-	}
-}
-
-/*
- *  this function is needed because the locking order
- *  device lock -> lcu lock
- *  needs to be assured when iterating over devices in an LCU
- *
- *  if a device is specified in pos then the device lock is already hold
- */
-static void _trylock_and_lock_lcu_irqsave(struct alias_lcu *lcu,
-					  struct dasd_device *pos,
-					  unsigned long *flags)
-{
-	struct dasd_device *failed;
-
-	do {
-		spin_lock_irqsave(&lcu->lock, *flags);
-		failed = _trylock_all_devices_on_lcu(lcu, pos);
-		if (failed) {
-			_unlock_all_devices_on_lcu(lcu, pos, failed);
-			spin_unlock_irqrestore(&lcu->lock, *flags);
-			cpu_relax();
-		}
-	} while (failed);
-}
-
-static void _trylock_and_lock_lcu(struct alias_lcu *lcu,
-				  struct dasd_device *pos)
-{
-	struct dasd_device *failed;
-
-	do {
-		spin_lock(&lcu->lock);
-		failed = _trylock_all_devices_on_lcu(lcu, pos);
-		if (failed) {
-			_unlock_all_devices_on_lcu(lcu, pos, failed);
-			spin_unlock(&lcu->lock);
-			cpu_relax();
-		}
-	} while (failed);
-}
-
 static int read_unit_address_configuration(struct dasd_device *device,
 					   struct alias_lcu *lcu)
 {
@@ -615,7 +491,7 @@ static int _lcu_update(struct dasd_device *refdev, struct alias_lcu *lcu)
 	if (rc)
 		return rc;
 
-	_trylock_and_lock_lcu_irqsave(lcu, NULL, &flags);
+	spin_lock_irqsave(&lcu->lock, flags);
 	lcu->pav = NO_PAV;
 	for (i = 0; i < MAX_DEVICES_PER_LCU; ++i) {
 		switch (lcu->uac->unit[i].ua_type) {
@@ -634,7 +510,6 @@ static int _lcu_update(struct dasd_device *refdev, struct alias_lcu *lcu)
 				 alias_list) {
 		_add_device_to_lcu(lcu, device, refdev);
 	}
-	_unlock_all_devices_on_lcu(lcu, NULL, NULL);
 	spin_unlock_irqrestore(&lcu->lock, flags);
 	return 0;
 }
@@ -722,8 +597,7 @@ int dasd_alias_add_device(struct dasd_device *device)
 
 	lcu = private->lcu;
 	rc = 0;
-	spin_lock_irqsave(get_ccwdev_lock(device->cdev), flags);
-	spin_lock(&lcu->lock);
+	spin_lock_irqsave(&lcu->lock, flags);
 	if (!(lcu->flags & UPDATE_PENDING)) {
 		rc = _add_device_to_lcu(lcu, device, device);
 		if (rc)
@@ -733,8 +607,7 @@ int dasd_alias_add_device(struct dasd_device *device)
 		list_move(&device->alias_list, &lcu->active_devices);
 		_schedule_lcu_update(lcu, device);
 	}
-	spin_unlock(&lcu->lock);
-	spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
+	spin_unlock_irqrestore(&lcu->lock, flags);
 	return rc;
 }
 
@@ -933,15 +806,27 @@ static void _stop_all_devices_on_lcu(struct alias_lcu *lcu)
 	struct alias_pav_group *pavgroup;
 	struct dasd_device *device;
 
-	list_for_each_entry(device, &lcu->active_devices, alias_list)
+	list_for_each_entry(device, &lcu->active_devices, alias_list) {
+		spin_lock(get_ccwdev_lock(device->cdev));
 		dasd_device_set_stop_bits(device, DASD_STOPPED_SU);
-	list_for_each_entry(device, &lcu->inactive_devices, alias_list)
+		spin_unlock(get_ccwdev_lock(device->cdev));
+	}
+	list_for_each_entry(device, &lcu->inactive_devices, alias_list) {
+		spin_lock(get_ccwdev_lock(device->cdev));
 		dasd_device_set_stop_bits(device, DASD_STOPPED_SU);
+		spin_unlock(get_ccwdev_lock(device->cdev));
+	}
 	list_for_each_entry(pavgroup, &lcu->grouplist, group) {
-		list_for_each_entry(device, &pavgroup->baselist, alias_list)
+		list_for_each_entry(device, &pavgroup->baselist, alias_list) {
+			spin_lock(get_ccwdev_lock(device->cdev));
 			dasd_device_set_stop_bits(device, DASD_STOPPED_SU);
-		list_for_each_entry(device, &pavgroup->aliaslist, alias_list)
+			spin_unlock(get_ccwdev_lock(device->cdev));
+		}
+		list_for_each_entry(device, &pavgroup->aliaslist, alias_list) {
+			spin_lock(get_ccwdev_lock(device->cdev));
 			dasd_device_set_stop_bits(device, DASD_STOPPED_SU);
+			spin_unlock(get_ccwdev_lock(device->cdev));
+		}
 	}
 }
 
@@ -950,15 +835,27 @@ static void _unstop_all_devices_on_lcu(struct alias_lcu *lcu)
 	struct alias_pav_group *pavgroup;
 	struct dasd_device *device;
 
-	list_for_each_entry(device, &lcu->active_devices, alias_list)
+	list_for_each_entry(device, &lcu->active_devices, alias_list) {
+		spin_lock(get_ccwdev_lock(device->cdev));
 		dasd_device_remove_stop_bits(device, DASD_STOPPED_SU);
-	list_for_each_entry(device, &lcu->inactive_devices, alias_list)
+		spin_unlock(get_ccwdev_lock(device->cdev));
+	}
+	list_for_each_entry(device, &lcu->inactive_devices, alias_list) {
+		spin_lock(get_ccwdev_lock(device->cdev));
 		dasd_device_remove_stop_bits(device, DASD_STOPPED_SU);
+		spin_unlock(get_ccwdev_lock(device->cdev));
+	}
 	list_for_each_entry(pavgroup, &lcu->grouplist, group) {
-		list_for_each_entry(device, &pavgroup->baselist, alias_list)
+		list_for_each_entry(device, &pavgroup->baselist, alias_list) {
+			spin_lock(get_ccwdev_lock(device->cdev));
 			dasd_device_remove_stop_bits(device, DASD_STOPPED_SU);
-		list_for_each_entry(device, &pavgroup->aliaslist, alias_list)
+			spin_unlock(get_ccwdev_lock(device->cdev));
+		}
+		list_for_each_entry(device, &pavgroup->aliaslist, alias_list) {
+			spin_lock(get_ccwdev_lock(device->cdev));
 			dasd_device_remove_stop_bits(device, DASD_STOPPED_SU);
+			spin_unlock(get_ccwdev_lock(device->cdev));
+		}
 	}
 }
 
@@ -984,48 +881,32 @@ static void summary_unit_check_handling_work(struct work_struct *work)
 	spin_unlock_irqrestore(get_ccwdev_lock(device->cdev), flags);
 	reset_summary_unit_check(lcu, device, suc_data->reason);
 
-	_trylock_and_lock_lcu_irqsave(lcu, NULL, &flags);
+	spin_lock_irqsave(&lcu->lock, flags);
 	_unstop_all_devices_on_lcu(lcu);
 	_restart_all_base_devices_on_lcu(lcu);
 	/* 3. read new alias configuration */
 	_schedule_lcu_update(lcu, device);
 	lcu->suc_data.device = NULL;
 	dasd_put_device(device);
-	_unlock_all_devices_on_lcu(lcu, NULL, NULL);
 	spin_unlock_irqrestore(&lcu->lock, flags);
 }
 
-/*
- * note: this will be called from int handler context (cdev locked)
- */
-void dasd_alias_handle_summary_unit_check(struct dasd_device *device,
-					  struct irb *irb)
+void dasd_alias_handle_summary_unit_check(struct work_struct *work)
 {
+	struct dasd_device *device = container_of(work, struct dasd_device,
+						  suc_work);
 	struct dasd_eckd_private *private = device->private;
 	struct alias_lcu *lcu;
-	char reason;
-	char *sense;
-
-	sense = dasd_get_sense(irb);
-	if (sense) {
-		reason = sense[8];
-		DBF_DEV_EVENT(DBF_NOTICE, device, "%s %x",
-			    "eckd handle summary unit check: reason", reason);
-	} else {
-		DBF_DEV_EVENT(DBF_WARNING, device, "%s",
-			    "eckd handle summary unit check:"
-			    " no reason code available");
-		return;
-	}
+	unsigned long flags;
 
 	lcu = private->lcu;
 	if (!lcu) {
 		DBF_DEV_EVENT(DBF_WARNING, device, "%s",
 			    "device not ready to handle summary"
 			    " unit check (no lcu structure)");
-		return;
+		goto out;
 	}
-	_trylock_and_lock_lcu(lcu, device);
+	spin_lock_irqsave(&lcu->lock, flags);
 	/* If this device is about to be removed just return and wait for
 	 * the next interrupt on a different device
 	 */
@@ -1033,27 +914,26 @@ void dasd_alias_handle_summary_unit_check(struct dasd_device *device,
 		DBF_DEV_EVENT(DBF_WARNING, device, "%s",
 			    "device is in offline processing,"
 			    " don't do summary unit check handling");
-		_unlock_all_devices_on_lcu(lcu, device, NULL);
-		spin_unlock(&lcu->lock);
-		return;
+		goto out_unlock;
 	}
 	if (lcu->suc_data.device) {
 		/* already scheduled or running */
 		DBF_DEV_EVENT(DBF_WARNING, device, "%s",
 			    "previous instance of summary unit check worker"
 			    " still pending");
-		_unlock_all_devices_on_lcu(lcu, device, NULL);
-		spin_unlock(&lcu->lock);
-		return ;
+		goto out_unlock;
 	}
 	_stop_all_devices_on_lcu(lcu);
 	/* prepare for lcu_update */
-	private->lcu->flags |= NEED_UAC_UPDATE | UPDATE_PENDING;
-	lcu->suc_data.reason = reason;
+	lcu->flags |= NEED_UAC_UPDATE | UPDATE_PENDING;
+	lcu->suc_data.reason = private->suc_reason;
 	lcu->suc_data.device = device;
 	dasd_get_device(device);
-	_unlock_all_devices_on_lcu(lcu, device, NULL);
-	spin_unlock(&lcu->lock);
 	if (!schedule_work(&lcu->suc_data.worker))
 		dasd_put_device(device);
+out_unlock:
+	spin_unlock_irqrestore(&lcu->lock, flags);
+out:
+	clear_bit(DASD_FLAG_SUC, &device->flags);
+	dasd_put_device(device);
 };