[PATCH 4/4] scsi: remove direct device lookup per host

[Hannes Reinecke <hare@suse.de>]

Drop the per-host device list for direct lookup and iterate
over the targets and devices xarrays instead.
As both are now using xarrays the lookup is more efficient
as we can use the provided indices based on the HCTL id
to do a direct lookup instead of traversing lists.

Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 drivers/scsi/hosts.c       |  1 -
 drivers/scsi/scsi.c        | 67 +++++++++++++++++++++++++++++++++++++++++-----
 drivers/scsi/scsi_scan.c   | 20 ++++++++------
 drivers/scsi/scsi_sysfs.c  | 10 ++-----
 include/scsi/scsi_device.h | 13 +++++----
 include/scsi/scsi_host.h   |  3 +--
 6 files changed, 84 insertions(+), 30 deletions(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 7109afad0183..004a50a95560 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -382,7 +382,6 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
 	shost->host_lock = &shost->default_lock;
 	spin_lock_init(shost->host_lock);
 	shost->shost_state = SHOST_CREATED;
-	INIT_LIST_HEAD(&shost->__devices);
 	xa_init(&shost->__targets);
 	INIT_LIST_HEAD(&shost->eh_cmd_q);
 	INIT_LIST_HEAD(&shost->starved_list);
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index 9dbbc51a1eb5..eac505a169a7 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -554,18 +554,40 @@ EXPORT_SYMBOL(scsi_device_put);
 struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *shost,
 					   struct scsi_device *prev)
 {
-	struct list_head *list = (prev ? &prev->siblings : &shost->__devices);
+	struct scsi_target *starget;
 	struct scsi_device *next = NULL;
 	unsigned long flags;
+	unsigned long tid = 0, lun_idx = 0;
 
 	spin_lock_irqsave(shost->host_lock, flags);
-	while (list->next != &shost->__devices) {
-		next = list_entry(list->next, struct scsi_device, siblings);
-		/* skip devices that we can't get a reference to */
+	if (!prev) {
+		starget = xa_find(&shost->__targets, &tid,
+				       ULONG_MAX, XA_PRESENT);
+		if (starget) {
+			next = xa_find(&starget->devices, &lun_idx,
+				       ULONG_MAX, XA_PRESENT);
+			if (!scsi_device_get(next)) {
+				spin_unlock_irqrestore(shost->host_lock, flags);
+				return next;
+			}
+		}
+	} else {
+		starget = prev->sdev_target;
+		tid = (starget->channel << 16) | starget->id;
+		lun_idx = prev->lun_idx;
+	}
+	while (starget) {
+		next = xa_find_after(&starget->devices, &lun_idx,
+				     ULONG_MAX, XA_PRESENT);
+		if (!next) {
+			/* No more LUNs on this target, switch to the next */
+			lun_idx = 0;
+			starget = xa_find_after(&shost->__targets, &tid,
+						ULONG_MAX, XA_PRESENT);
+			continue;
+		}
 		if (!scsi_device_get(next))
 			break;
-		next = NULL;
-		list = list->next;
 	}
 	spin_unlock_irqrestore(shost->host_lock, flags);
 
@@ -575,6 +597,39 @@ struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *shost,
 }
 EXPORT_SYMBOL(__scsi_iterate_devices);
 
+/* helper for __shost_for_each_device, see that for documentation */
+struct scsi_device *__scsi_iterate_devices_unlocked(struct Scsi_Host *shost,
+						    struct scsi_device *prev)
+{
+	struct scsi_target *starget;
+	struct scsi_device *next = NULL;
+	unsigned long tid = 0, lun_idx = 0;
+
+	if (!prev) {
+		starget = xa_find(&shost->__targets, &tid,
+				       ULONG_MAX, XA_PRESENT);
+		if (starget)
+			return xa_find(&starget->devices, &lun_idx,
+				       ULONG_MAX, XA_PRESENT);
+	} else {
+		starget = prev->sdev_target;
+		tid = (starget->channel << 16) | starget->id;
+		lun_idx = prev->lun_idx;
+	}
+	while (starget) {
+		next = xa_find_after(&starget->devices, &lun_idx,
+				     ULONG_MAX, XA_PRESENT);
+		if (next)
+			return next;
+		/* No more LUNs on this target, switch to the next */
+		lun_idx = 0;
+		starget = xa_find_after(&shost->__targets, &tid,
+					ULONG_MAX, XA_PRESENT);
+	}
+	return NULL;
+}
+EXPORT_SYMBOL(__scsi_iterate_devices_unlocked);
+
 /**
  * __scsi_target_lookup  -  find a target based on channel and target id
  * @shost:	SCSI host pointer
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index c7aba9ba5c0c..e75e7f93f8f6 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -234,7 +234,6 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
 	sdev->channel = starget->channel;
 	mutex_init(&sdev->state_mutex);
 	sdev->sdev_state = SDEV_CREATED;
-	INIT_LIST_HEAD(&sdev->siblings);
 	INIT_LIST_HEAD(&sdev->starved_entry);
 	INIT_LIST_HEAD(&sdev->event_list);
 	spin_lock_init(&sdev->list_lock);
@@ -1847,17 +1846,22 @@ EXPORT_SYMBOL(scsi_scan_host);
 
 void scsi_forget_host(struct Scsi_Host *shost)
 {
+	struct scsi_target *starget;
 	struct scsi_device *sdev;
 	unsigned long flags;
+	unsigned long tid = 0;
 
- restart:
 	spin_lock_irqsave(shost->host_lock, flags);
-	list_for_each_entry(sdev, &shost->__devices, siblings) {
-		if (sdev->sdev_state == SDEV_DEL)
-			continue;
-		spin_unlock_irqrestore(shost->host_lock, flags);
-		__scsi_remove_device(sdev);
-		goto restart;
+	xa_for_each(&shost->__targets, tid, starget) {
+		unsigned long lun_id = 0;
+
+		xa_for_each(&starget->devices, lun_id, sdev) {
+			if (sdev->sdev_state == SDEV_DEL)
+				continue;
+			spin_unlock_irqrestore(shost->host_lock, flags);
+			__scsi_remove_device(sdev);
+			spin_lock_irqsave(shost->host_lock, flags);
+		}
 	}
 	spin_unlock_irqrestore(shost->host_lock, flags);
 }
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 27c19232f175..63fa57684782 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -449,7 +449,6 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 	parent = sdev->sdev_gendev.parent;
 
 	spin_lock_irqsave(sdev->host->host_lock, flags);
-	list_del(&sdev->siblings);
 	xa_erase(&starget->devices, sdev->lun_idx);
 	list_del(&sdev->starved_entry);
 	spin_unlock_irqrestore(sdev->host->host_lock, flags);
@@ -1476,19 +1475,16 @@ static void __scsi_remove_target(struct scsi_target *starget)
 	struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
 	unsigned long flags;
 	struct scsi_device *sdev;
+	unsigned long lun_idx = 0;
 
 	spin_lock_irqsave(shost->host_lock, flags);
- restart:
-	list_for_each_entry(sdev, &shost->__devices, siblings) {
+	xa_for_each(&starget->devices, lun_idx, sdev) {
 		/*
 		 * We cannot call scsi_device_get() here, as
 		 * we might've been called from rmmod() causing
 		 * scsi_device_get() to fail the module_is_live()
 		 * check.
 		 */
-		if (sdev->channel != starget->channel ||
-		    sdev->id != starget->id)
-			continue;
 		if (sdev->sdev_state == SDEV_DEL ||
 		    sdev->sdev_state == SDEV_CANCEL ||
 		    !get_device(&sdev->sdev_gendev))
@@ -1497,7 +1493,6 @@ static void __scsi_remove_target(struct scsi_target *starget)
 		scsi_remove_device(sdev);
 		put_device(&sdev->sdev_gendev);
 		spin_lock_irqsave(shost->host_lock, flags);
-		goto restart;
 	}
 	spin_unlock_irqrestore(shost->host_lock, flags);
 }
@@ -1635,7 +1630,6 @@ void scsi_sysfs_device_initialize(struct scsi_device *sdev)
 		WARN_ON(xa_alloc(&starget->devices, &sdev->lun_idx,
 				  sdev, scsi_lun_limit, GFP_KERNEL) < 0);
 	}
-	list_add_tail(&sdev->siblings, &shost->__devices);
 	spin_unlock_irqrestore(shost->host_lock, flags);
 	/*
 	 * device can now only be removed via __scsi_remove_device() so hold
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 2c6b9d8bc40e..b811b5e3adfe 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -102,9 +102,6 @@ struct scsi_device {
 	struct Scsi_Host *host;
 	struct request_queue *request_queue;
 
-	/* the next two are protected by the host->host_lock */
-	struct list_head    siblings;   /* list of all devices on this host */
-
 	atomic_t device_busy;		/* commands actually active on LLDD */
 	atomic_t device_blocked;	/* Device returned QUEUE_FULL. */
 
@@ -376,6 +373,10 @@ extern struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *,
 	     (sdev); \
 	     (sdev) = __scsi_iterate_devices((shost), (sdev)))
 
+/* only exposed to implement shost_for_each_device */
+struct scsi_device *__scsi_iterate_devices_unlocked(struct Scsi_Host *,
+						    struct scsi_device *);
+
 /**
  * __shost_for_each_device - iterate over all devices of a host (UNLOCKED)
  * @sdev: the &struct scsi_device to use as a cursor
@@ -389,8 +390,10 @@ extern struct scsi_device *__scsi_iterate_devices(struct Scsi_Host *,
  * device list in interrupt context.  Otherwise you really want to use
  * shost_for_each_device instead.
  */
-#define __shost_for_each_device(sdev, shost) \
-	list_for_each_entry((sdev), &((shost)->__devices), siblings)
+#define __shost_for_each_device(sdev, shost)				\
+	for((sdev) = __scsi_iterate_devices_unlocked((shost), NULL);	\
+	    (sdev);							\
+	    (sdev) = __scsi_iterate_devices_unlocked((shost),(sdev)))
 
 extern int scsi_change_queue_depth(struct scsi_device *, int);
 extern int scsi_track_queue_full(struct scsi_device *, int);
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index b9395676c75b..ee0b72075e9f 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -520,9 +520,8 @@ struct Scsi_Host {
 	 * their __ prefixed variants with the lock held. NEVER
 	 * access this list directly from a driver.
 	 */
-	struct list_head	__devices;
 	struct xarray		__targets;
-	
+
 	struct list_head	starved_list;
 
 	spinlock_t		default_lock;
-- 
2.16.4