[SCSI] libsas: introduce sas_drain_work()

When an lldd invokes ->notify_port_event() it can trigger a chain of libsas
events to:

  1/ form the port and find the direct attached device

  2/ if the attached device is an expander perform domain discovery

A call to flush_workqueue() will only flush the initial port formation work.
Currently libsas users need to call scsi_flush_work() up to the max depth of
chain (which will grow from 2 to 3 when ata discovery is moved to its own
discovery event).  Instead of open coding multiple calls switch to use
drain_workqueue() to flush sas work.

drain_workqueue() does not handle new work submitted during the drain so
libsas needs a bit of infrastructure to hold off unchained work submissions
while a drain is in flight.  A lldd ->notify() event is considered 'unchained'
while a sas_discover_event() is 'chained'.  As Tejun notes:

  "For now, I think it would be best to add private wrapper in libsas to
   support deferring unchained work items while draining."

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/include/scsi/libsas.h b/include/scsi/libsas.h
index 8e402d5a0640..42900fa95a03 100644
--- a/include/scsi/libsas.h
+++ b/include/scsi/libsas.h
@@ -330,6 +330,7 @@ struct sas_ha_event {
 
 enum sas_ha_state {
 	SAS_HA_REGISTERED,
+	SAS_HA_DRAINING,
 };
 
 struct sas_ha_struct {
@@ -337,6 +338,8 @@ struct sas_ha_struct {
 	struct sas_ha_event ha_events[HA_NUM_EVENTS];
 	unsigned long	 pending;
 
+	struct list_head  defer_q; /* work queued while draining */
+	struct mutex	  drain_mutex;
 	unsigned long	  state;
 	spinlock_t 	  state_lock;
 
@@ -657,6 +660,7 @@ int sas_eh_bus_reset_handler(struct scsi_cmnd *cmd);
 extern void sas_target_destroy(struct scsi_target *);
 extern int sas_slave_alloc(struct scsi_device *);
 extern int sas_ioctl(struct scsi_device *sdev, int cmd, void __user *arg);
+extern int sas_drain_work(struct sas_ha_struct *ha);
 
 extern int sas_smp_handler(struct Scsi_Host *shost, struct sas_rphy *rphy,
 			   struct request *req);