[PATCH 3.16 267/366] scsi: zfcp: fix infinite iteration on ERP ready list

Ben Hutchings
2018-10-14T23:12:02Z

From: Jens Remus <jremus@linux.ibm.com>

commit fa89adba1941e4f3b213399b81732a5c12fd9131 upstream.

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")
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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/s390/scsi/zfcp_dbf.c | 23 ++++++++++++++++++++++-
drivers/s390/scsi/zfcp_ext.h | 5 ++++-
drivers/s390/scsi/zfcp_scsi.c | 14 +++++++-------
3 files changed, 33 insertions(+), 9 deletions(-)

--- a/drivers/s390/scsi/zfcp_dbf.c
+++ b/drivers/s390/scsi/zfcp_dbf.c
@@ -3,7 +3,7 @@
*
* Debug traces for zfcp.
*
- * Copyright IBM Corp. 2002, 2017
+ * Copyright IBM Corp. 2002, 2018
*/

#define KMSG_COMPONENT "zfcp"
@@ -287,6 +287,27 @@ void zfcp_dbf_rec_trig(char *tag, struct
spin_unlock_irqrestore(&dbf->rec_lock, flags);
}

+/**
+ * zfcp_dbf_rec_trig_lock - trace event related to triggered recovery with lock
+ * @tag: identifier for event
+ * @adapter: adapter on which the erp_action should run
+ * @port: remote port involved in the erp_action
+ * @sdev: scsi device involved in the erp_action
+ * @want: wanted erp_action
+ * @need: required erp_action
+ *
+ * The adapter->erp_lock must not be held.
+ */
+void zfcp_dbf_rec_trig_lock(char *tag, struct zfcp_adapter *adapter,
+ struct zfcp_port *port, struct scsi_device *sdev,
+ u8 want, u8 need)
+{
+ unsigned long flags;
+
+ read_lock_irqsave(&adapter->erp_lock, flags);
+ zfcp_dbf_rec_trig(tag, adapter, port, sdev, want, need);
+ read_unlock_irqrestore(&adapter->erp_lock, flags);
+}

/**
* zfcp_dbf_rec_run_lvl - trace event related to running recovery
--- a/drivers/s390/scsi/zfcp_ext.h
+++ b/drivers/s390/scsi/zfcp_ext.h
@@ -3,7 +3,7 @@
*
* External function declarations.
*
- * Copyright IBM Corp. 2002, 2016
+ * Copyright IBM Corp. 2002, 2018
*/

#ifndef ZFCP_EXT_H
@@ -34,6 +34,9 @@ extern int zfcp_dbf_adapter_register(str
extern void zfcp_dbf_adapter_unregister(struct zfcp_adapter *);
extern void zfcp_dbf_rec_trig(char *, struct zfcp_adapter *,
struct zfcp_port *, struct scsi_device *, u8, u8);
+extern void zfcp_dbf_rec_trig_lock(char *tag, struct zfcp_adapter *adapter,
+ struct zfcp_port *port,
+ struct scsi_device *sdev, u8 want, u8 need);
extern void zfcp_dbf_rec_run(char *, struct zfcp_erp_action *);
extern void zfcp_dbf_rec_run_lvl(int level, char *tag,
struct zfcp_erp_action *erp);
--- a/drivers/s390/scsi/zfcp_scsi.c
+++ b/drivers/s390/scsi/zfcp_scsi.c
@@ -3,7 +3,7 @@
*
* Interface to Linux SCSI midlayer.
*
- * Copyright IBM Corp. 2002, 2017
+ * Copyright IBM Corp. 2002, 2018
*/

#define KMSG_COMPONENT "zfcp"
@@ -637,9 +637,9 @@ static void zfcp_scsi_rport_register(str
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,
@@ -661,9 +661,9 @@ static void zfcp_scsi_rport_block(struct
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;
}