From: Jens Remus jremus@linux.ibm.com

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 ---

James, Martin,

this is an important zfcp regression fix. It would be nice if it could make it into 4.17-rcX. The patch applies to James' fixes branch or Martin's 4.17/scsi-fixes branch.

Regards, Steffen

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(-)

diff --git a/drivers/s390/scsi/zfcp_dbf.c b/drivers/s390/scsi/zfcp_dbf.c index a8b831000b2d..18c4f933e8b9 100644 --- a/drivers/s390/scsi/zfcp_dbf.c +++ b/drivers/s390/scsi/zfcp_dbf.c @@ -4,7 +4,7 @@ * * Debug traces for zfcp. * - * Copyright IBM Corp. 2002, 2017 + * Copyright IBM Corp. 2002, 2018 */

#define KMSG_COMPONENT "zfcp" @@ -308,6 +308,27 @@ void zfcp_dbf_rec_trig(char *tag, struct zfcp_adapter *adapter, 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 diff --git a/drivers/s390/scsi/zfcp_ext.h b/drivers/s390/scsi/zfcp_ext.h index bf8ea4df2bb8..e5eed8aac0ce 100644 --- a/drivers/s390/scsi/zfcp_ext.h +++ b/drivers/s390/scsi/zfcp_ext.h @@ -4,7 +4,7 @@ * * External function declarations. * - * Copyright IBM Corp. 2002, 2016 + * Copyright IBM Corp. 2002, 2018 */

#ifndef ZFCP_EXT_H @@ -35,6 +35,9 @@ extern int zfcp_dbf_adapter_register(struct zfcp_adapter *); 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); 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; }