scsi: zfcp: fix infinite iteration on ERP ready list

zfcp_erp_adapter_reopen() schedules blocking of all of the adapter's
rports via zfcp_scsi_schedule_rports_block() and enqueues a reopen
adapter ERP action via zfcp_erp_action_enqueue(). Both are separately
processed asynchronously and concurrently.

Blocking of rports is done in a kworker by zfcp_scsi_rport_work(). It
calls zfcp_scsi_rport_block(), which then traces a DBF REC "scpdely" via
zfcp_dbf_rec_trig().  zfcp_dbf_rec_trig() acquires the DBF REC spin lock
and then iterates with list_for_each() over the adapter's ERP ready list
without holding the ERP lock. This opens a race window in which the
current list entry can be moved to another list, causing list_for_each()
to iterate forever on the wrong list, as the erp_ready_head is never
encountered as terminal condition.

Meanwhile the ERP action can be processed in the ERP thread by
zfcp_erp_thread(). It calls zfcp_erp_strategy(), which acquires the ERP
lock and then calls zfcp_erp_action_to_running() to move the ERP action
from the ready to the running list.  zfcp_erp_action_to_running() can
move the ERP action using list_move() just during the aforementioned
race window. It then traces a REC RUN "erator1" via zfcp_dbf_rec_run().
zfcp_dbf_rec_run() tries to acquire the DBF REC spin lock. If this is
held by the infinitely looping kworker, it effectively spins forever.

Example Sequence Diagram:

Process                ERP Thread             rport_work
-------------------    -------------------    -------------------
zfcp_erp_adapter_reopen()
zfcp_erp_adapter_block()
zfcp_scsi_schedule_rports_block()
lock ERP                                      zfcp_scsi_rport_work()
zfcp_erp_action_enqueue(ZFCP_ERP_ACTION_REOPEN_ADAPTER)
list_add_tail() on ready                      !(rport_task==RPORT_ADD)
wake_up() ERP thread                          zfcp_scsi_rport_block()
zfcp_dbf_rec_trig()    zfcp_erp_strategy()    zfcp_dbf_rec_trig()
unlock ERP                                    lock DBF REC
zfcp_erp_wait()        lock ERP
|                      zfcp_erp_action_to_running()
|                                             list_for_each() ready
|                      list_move()              current entry
|                        ready to running
|                      zfcp_dbf_rec_run()       endless loop over running
|                      zfcp_dbf_rec_run_lvl()
|                      lock DBF REC spins forever

Any adapter recovery can trigger this, such as setting the device offline
or reboot.

V4.9 commit 4eeaa4f3f1d6 ("zfcp: close window with unblocked rport
during rport gone") introduced additional tracing of (un)blocking of
rports. It missed that the adapter->erp_lock must be held when calling
zfcp_dbf_rec_trig().

This fix uses the approach formerly introduced by commit aa0fec62391c
("[SCSI] zfcp: Fix sparse warning by providing new entry in dbf") that got
later removed by commit ae0904f60fab ("[SCSI] zfcp: Redesign of the debug
tracing for recovery actions.").

Introduce zfcp_dbf_rec_trig_lock(), a wrapper for zfcp_dbf_rec_trig() that
acquires and releases the adapter->erp_lock for read.

Reported-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
Fixes: 4eeaa4f3f1d6 ("zfcp: close window with unblocked rport during rport gone")
Cc: <stable@vger.kernel.org> # 2.6.32+
Reviewed-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 7 insertions, 7 deletions

diff --git a/drivers/s390/scsi/zfcp_scsi.c b/drivers/s390/scsi/zfcp_scsi.c
index 4d2ba5682493..22f9562f415c 100644
--- a/drivers/s390/scsi/zfcp_scsi.c
+++ b/drivers/s390/scsi/zfcp_scsi.c
@@ -4,7 +4,7 @@
  *
  * Interface to Linux SCSI midlayer.
  *
- * Copyright IBM Corp. 2002, 2017
+ * Copyright IBM Corp. 2002, 2018
  */
 
 #define KMSG_COMPONENT "zfcp"
@@ -618,9 +618,9 @@ static void zfcp_scsi_rport_register(struct zfcp_port *port)
 	ids.port_id = port->d_id;
 	ids.roles = FC_RPORT_ROLE_FCP_TARGET;
 
-	zfcp_dbf_rec_trig("scpaddy", port->adapter, port, NULL,
-			  ZFCP_PSEUDO_ERP_ACTION_RPORT_ADD,
-			  ZFCP_PSEUDO_ERP_ACTION_RPORT_ADD);
+	zfcp_dbf_rec_trig_lock("scpaddy", port->adapter, port, NULL,
+			       ZFCP_PSEUDO_ERP_ACTION_RPORT_ADD,
+			       ZFCP_PSEUDO_ERP_ACTION_RPORT_ADD);
 	rport = fc_remote_port_add(port->adapter->scsi_host, 0, &ids);
 	if (!rport) {
 		dev_err(&port->adapter->ccw_device->dev,
@@ -642,9 +642,9 @@ static void zfcp_scsi_rport_block(struct zfcp_port *port)
 	struct fc_rport *rport = port->rport;
 
 	if (rport) {
-		zfcp_dbf_rec_trig("scpdely", port->adapter, port, NULL,
-				  ZFCP_PSEUDO_ERP_ACTION_RPORT_DEL,
-				  ZFCP_PSEUDO_ERP_ACTION_RPORT_DEL);
+		zfcp_dbf_rec_trig_lock("scpdely", port->adapter, port, NULL,
+				       ZFCP_PSEUDO_ERP_ACTION_RPORT_DEL,
+				       ZFCP_PSEUDO_ERP_ACTION_RPORT_DEL);
 		fc_remote_port_delete(rport);
 		port->rport = NULL;
 	}