[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, 5 insertions, 0 deletions

diff --git a/drivers/s390/scsi/zfcp_def.h b/drivers/s390/scsi/zfcp_def.h
index 32933ed54b8a..07b0957b82f3 100644
--- a/drivers/s390/scsi/zfcp_def.h
+++ b/drivers/s390/scsi/zfcp_def.h
@@ -637,6 +637,7 @@ do { \
 #define ZFCP_STATUS_UNIT_SHARED                 0x00000004
 #define ZFCP_STATUS_UNIT_READONLY               0x00000008
 #define ZFCP_STATUS_UNIT_REGISTERED             0x00000010
+#define ZFCP_STATUS_UNIT_SCSI_WORK_PENDING      0x00000020
 
 /* FSF request status (this does not have a common part) */
 #define ZFCP_STATUS_FSFREQ_NOT_INIT             0x00000000
@@ -980,6 +981,10 @@ struct zfcp_unit {
         struct scsi_device     *device;        /* scsi device struct pointer */
         struct zfcp_erp_action erp_action;     /* pending error recovery */
         atomic_t               erp_counter;
+        wait_queue_head_t      scsi_scan_wq;   /* can be used to wait until
+                                                  all scsi_scan_target
+                                                  requests have been
+                                                  completed. */
 };
 
 /* FSF request */