[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, 0 insertions, 14 deletions

diff --git a/drivers/scsi/libsas/sas_internal.h b/drivers/scsi/libsas/sas_internal.h
index 1fd84b3f091..948ea64cc2e 100644
--- a/drivers/scsi/libsas/sas_internal.h
+++ b/drivers/scsi/libsas/sas_internal.h
@@ -92,20 +92,6 @@ static inline int sas_smp_host_handler(struct Scsi_Host *shost,
 }
 #endif
 
-static inline void sas_queue_event(int event, unsigned long *pending,
-				   struct work_struct *work,
-				   struct sas_ha_struct *sas_ha)
-{
-	if (!test_and_set_bit(event, pending)) {
-		unsigned long flags;
-
-		spin_lock_irqsave(&sas_ha->state_lock, flags);
-		if (test_bit(SAS_HA_REGISTERED, &sas_ha->state))
-			scsi_queue_work(sas_ha->core.shost, work);
-		spin_unlock_irqrestore(&sas_ha->state_lock, flags);
-	}
-}
-
 static inline void sas_fill_in_rphy(struct domain_device *dev,
 				    struct sas_rphy *rphy)
 {