[SCSI] libsas: fix sas_find_local_phy(), take phy references

In the direct-attached case this routine returns the phy on which this
device was first discovered.  Which is broken if we want to support
wide-targets, as this phy reference can become stale even though the
port is still active.

In the expander-attached case this routine tries to lookup the phy by
scanning the attached sas addresses of the parent expander, and BUG_ONs
if it can't find it.  However since eh and the libsas workqueue run
independently we can still be attempting device recovery via eh after
libsas has recorded the device as detached.  This is even easier to hit
now that eh is blocked while device domain rediscovery takes place, and
that libata is fed more timed out commands increasing the chances that
it will try to recover the ata device.

Arrange for dev->phy to always point to a last known good phy, it may be
stale after the port is torn down, but it will catch up for wide port
reconfigurations, and never be NULL.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/drivers/scsi/scsi_transport_sas.c b/drivers/scsi/scsi_transport_sas.c
index ab3bd0b..7d69a25 100644
--- a/drivers/scsi/scsi_transport_sas.c
+++ b/drivers/scsi/scsi_transport_sas.c
@@ -1060,6 +1060,29 @@ int scsi_is_sas_port(const struct device *dev)
 EXPORT_SYMBOL(scsi_is_sas_port);
 
 /**
+ * sas_port_get_phy - try to take a reference on a port member
+ * @port: port to check
+ */
+struct sas_phy *sas_port_get_phy(struct sas_port *port)
+{
+	struct sas_phy *phy;
+
+	mutex_lock(&port->phy_list_mutex);
+	if (list_empty(&port->phy_list))
+		phy = NULL;
+	else {
+		struct list_head *ent = port->phy_list.next;
+
+		phy = list_entry(ent, typeof(*phy), port_siblings);
+		get_device(&phy->dev);
+	}
+	mutex_unlock(&port->phy_list_mutex);
+
+	return phy;
+}
+EXPORT_SYMBOL(sas_port_get_phy);
+
+/**
  * sas_port_add_phy - add another phy to a port to form a wide port
  * @port:	port to add the phy to
  * @phy:	phy to add