[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, 55 insertions, 0 deletions

diff --git a/drivers/scsi/libsas/sas_event.c b/drivers/scsi/libsas/sas_event.c
index 9c084bc09bbd..e5035aa4c2a6 100644
--- a/drivers/scsi/libsas/sas_event.c
+++ b/drivers/scsi/libsas/sas_event.c
@@ -22,10 +22,65 @@
  *
  */
 
+#include <linux/export.h>
 #include <scsi/scsi_host.h>
 #include "sas_internal.h"
 #include "sas_dump.h"
 
+static void sas_queue_work(struct sas_ha_struct *ha, struct work_struct *work)
+{
+	if (!test_bit(SAS_HA_REGISTERED, &ha->state))
+		return;
+
+	if (test_bit(SAS_HA_DRAINING, &ha->state))
+		list_add(&work->entry, &ha->defer_q);
+	else
+		scsi_queue_work(ha->core.shost, work);
+}
+
+static void sas_queue_event(int event, unsigned long *pending,
+			    struct work_struct *work,
+			    struct sas_ha_struct *ha)
+{
+	if (!test_and_set_bit(event, pending)) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&ha->state_lock, flags);
+		sas_queue_work(ha, work);
+		spin_unlock_irqrestore(&ha->state_lock, flags);
+	}
+}
+
+int sas_drain_work(struct sas_ha_struct *ha)
+{
+	struct workqueue_struct *wq = ha->core.shost->work_q;
+	struct work_struct *w, *_w;
+	int err;
+
+	err = mutex_lock_interruptible(&ha->drain_mutex);
+	if (err)
+		return err;
+
+	set_bit(SAS_HA_DRAINING, &ha->state);
+	/* flush submitters */
+	spin_lock_irq(&ha->state_lock);
+	spin_unlock_irq(&ha->state_lock);
+
+	drain_workqueue(wq);
+
+	spin_lock_irq(&ha->state_lock);
+	clear_bit(SAS_HA_DRAINING, &ha->state);
+	list_for_each_entry_safe(w, _w, &ha->defer_q, entry) {
+		list_del_init(&w->entry);
+		sas_queue_work(ha, w);
+	}
+	spin_unlock_irq(&ha->state_lock);
+	mutex_unlock(&ha->drain_mutex);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(sas_drain_work);
+
 static void notify_ha_event(struct sas_ha_struct *sas_ha, enum ha_event event)
 {
 	BUG_ON(event >= HA_NUM_EVENTS);