mpt2sas: Refcount sas_device objects and fix unsafe list usage

These objects can be referenced concurrently throughout the driver, we
need a way to make sure threads can't delete them out from under each
other. This patch adds the refcount, and refactors the code to use it.

Additionally, we cannot iterate over the sas_device_list without
holding the lock, or we risk corrupting random memory if items are
added or deleted as we iterate. This patch refactors _scsih_probe_sas()
to use the sas_device_list in a safe way.
Signed-off-by: Calvin Owens <calvinowens@fb.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nicholas Bellinger <nab@linux-iscsi.org>
Tested-by: Chaitra Basappa <chaitra.basappa@avagotech.com>
Acked-by: Sreekanth Reddy <sreekanth.reddy@avagotech.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>

drivers/scsi/mpt2sas/mpt2sas_base.h

@@ -238,6 +238,7 @@
  * @flags: MPT_TARGET_FLAGS_XXX flags
  * @deleted: target flaged for deletion
  * @tm_busy: target is busy with TM request.
+ * @sdev: The sas_device associated with this target
  */
 struct MPT2SAS_TARGET {
 	struct scsi_target *starget;
@@ -248,6 +249,7 @@ struct MPT2SAS_TARGET {
 	u32	flags;
 	u8	deleted;
 	u8	tm_busy;
+	struct _sas_device *sdev;
 };
 
 
@@ -376,8 +378,24 @@ struct _sas_device {
 	u8	phy;
 	u8	responding;
 	u8	pfa_led_on;
+	struct kref refcount;
 };
 
+static inline void sas_device_get(struct _sas_device *s)
+{
+	kref_get(&s->refcount);
+}
+
+static inline void sas_device_free(struct kref *r)
+{
+	kfree(container_of(r, struct _sas_device, refcount));
+}
+
+static inline void sas_device_put(struct _sas_device *s)
+{
+	kref_put(&s->refcount, sas_device_free);
+}
+
 /**
  * struct _raid_device - raid volume link list
  * @list: sas device list
@@ -1095,7 +1113,9 @@ struct _sas_node *mpt2sas_scsih_expander_find_by_handle(struct MPT2SAS_ADAPTER *
     u16 handle);
 struct _sas_node *mpt2sas_scsih_expander_find_by_sas_address(struct MPT2SAS_ADAPTER
     *ioc, u64 sas_address);
-struct _sas_device *mpt2sas_scsih_sas_device_find_by_sas_address(
+struct _sas_device *mpt2sas_get_sdev_by_addr(
+    struct MPT2SAS_ADAPTER *ioc, u64 sas_address);
+struct _sas_device *__mpt2sas_get_sdev_by_addr(
     struct MPT2SAS_ADAPTER *ioc, u64 sas_address);
 
 void mpt2sas_port_enable_complete(struct MPT2SAS_ADAPTER *ioc);

drivers/scsi/mpt2sas/mpt2sas_transport.c

@@ -1323,15 +1323,17 @@ _transport_get_enclosure_identifier(struct sas_rphy *rphy, u64 *identifier)
 	int rc;
 
 	spin_lock_irqsave(&ioc->sas_device_lock, flags);
-	sas_device = mpt2sas_scsih_sas_device_find_by_sas_address(ioc,
+	sas_device = __mpt2sas_get_sdev_by_addr(ioc,
 	    rphy->identify.sas_address);
 	if (sas_device) {
 		*identifier = sas_device->enclosure_logical_id;
 		rc = 0;
+		sas_device_put(sas_device);
 	} else {
 		*identifier = 0;
 		rc = -ENXIO;
 	}
+
 	spin_unlock_irqrestore(&ioc->sas_device_lock, flags);
 	return rc;
 }
@@ -1351,12 +1353,14 @@ _transport_get_bay_identifier(struct sas_rphy *rphy)
 	int rc;
 
 	spin_lock_irqsave(&ioc->sas_device_lock, flags);
-	sas_device = mpt2sas_scsih_sas_device_find_by_sas_address(ioc,
+	sas_device = __mpt2sas_get_sdev_by_addr(ioc,
 	    rphy->identify.sas_address);
-	if (sas_device)
+	if (sas_device) {
 		rc = sas_device->slot;
-	else
+		sas_device_put(sas_device);
+	} else {
 		rc = -ENXIO;
+	}
 	spin_unlock_irqrestore(&ioc->sas_device_lock, flags);
 	return rc;
 }