[SCSI] zfcp: Fix deadlock between zfcp ERP and SCSI

The SCSI stack requires low level drivers to register and
unregister devices. For zfcp this leads to the situation where
zfcp calls the SCSI stack, the SCSI tries to scan the new device
and the scan SCSI command fails. This would require the zfcp erp,
but the erp thread is already blocked in the register call.

The fix is to make sure that the calls from the ERP thread to
the SCSI stack do not block the ERP thread. In detail:
1) Use a workqueue to avoid blocking of the scsi_scan_target calls.
2) When removing a unit make sure that no scsi_scan_target call is
   pending.
3) Replace scsi_flush_work with scsi_target_unblock. This avoids
   blocking and has the same result.

Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>

1 files changed, 60 insertions, 4 deletions

diff --git a/drivers/s390/scsi/zfcp_erp.c b/drivers/s390/scsi/zfcp_erp.c
index f326bbe49fa7..885572300589 100644
--- a/drivers/s390/scsi/zfcp_erp.c
+++ b/drivers/s390/scsi/zfcp_erp.c
@@ -1591,6 +1591,62 @@ zfcp_erp_strategy_check_adapter(struct zfcp_adapter *adapter, int result)
         return result;
 }
 
+struct zfcp_erp_add_work {
+        struct zfcp_unit  *unit;
+        struct work_struct work;
+};
+
+/**
+ * zfcp_erp_scsi_scan
+ * @data: pointer to a struct zfcp_erp_add_work
+ *
+ * Registers a logical unit with the SCSI stack.
+ */
+static void zfcp_erp_scsi_scan(struct work_struct *work)
+{
+        struct zfcp_erp_add_work *p =
+                container_of(work, struct zfcp_erp_add_work, work);
+        struct zfcp_unit *unit = p->unit;
+        struct fc_rport *rport = unit->port->rport;
+        scsi_scan_target(&rport->dev, 0, rport->scsi_target_id,
+                         unit->scsi_lun, 0);
+        atomic_clear_mask(ZFCP_STATUS_UNIT_SCSI_WORK_PENDING, &unit->status);
+        wake_up(&unit->scsi_scan_wq);
+        zfcp_unit_put(unit);
+        kfree(p);
+}
+
+/**
+ * zfcp_erp_schedule_work
+ * @unit: pointer to unit which should be registered with SCSI stack
+ *
+ * Schedules work which registers a unit with the SCSI stack
+ */
+static void
+zfcp_erp_schedule_work(struct zfcp_unit *unit)
+{
+        struct zfcp_erp_add_work *p;
+
+        p = kmalloc(sizeof(*p), GFP_KERNEL);
+        if (!p) {
+                ZFCP_LOG_NORMAL("error: Out of resources. Could not register "
+                                "the FCP-LUN 0x%Lx connected to "
+                                "the port with WWPN 0x%Lx connected to "
+                                "the adapter %s with the SCSI stack.\n",
+                                unit->fcp_lun,
+                                unit->port->wwpn,
+                                zfcp_get_busid_by_unit(unit));
+                return;
+        }
+
+        zfcp_unit_get(unit);
+        memset(p, 0, sizeof(*p));
+        atomic_set_mask(ZFCP_STATUS_UNIT_SCSI_WORK_PENDING, &unit->status);
+        INIT_WORK(&p->work, zfcp_erp_scsi_scan);
+        p->unit = unit;
+        schedule_work(&p->work);
+}
+
 /*
  * function:    
  *
@@ -3092,9 +3148,9 @@ zfcp_erp_action_cleanup(int action, struct zfcp_adapter *adapter,
                     && port->rport) {
                         atomic_set_mask(ZFCP_STATUS_UNIT_REGISTERED,
                                         &unit->status);
-                        scsi_scan_target(&port->rport->dev, 0,
-                                         port->rport->scsi_target_id,
-                                         unit->scsi_lun, 0);
+                        if (atomic_test_mask(ZFCP_STATUS_UNIT_SCSI_WORK_PENDING,
+                                             &unit->status) == 0)
+                                zfcp_erp_schedule_work(unit);
                 }
                 zfcp_unit_put(unit);
                 break;
@@ -3121,7 +3177,7 @@ zfcp_erp_action_cleanup(int action, struct zfcp_adapter *adapter,
                                                 zfcp_get_busid_by_port(port),
                                                 port->wwpn);
                         else {
-                                scsi_flush_work(adapter->scsi_host);
+                                scsi_target_unblock(&port->rport->dev);
                                 port->rport->maxframe_size = port->maxframe_size;
                                 port->rport->supported_classes =
                                         port->supported_classes;