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[SCSI] libsas: introduce sas_drain_work()

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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>
This commit is contained in:
Dan Williams
2011-12-19 16:42:34 -08:00
committed by James Bottomley
parent f8daa6e6d8
commit b1124cd3ec
9 changed files with 93 additions and 26 deletions
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4
include/scsi/libsas.h
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@@ -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);