isci: atomic device lookup and reference counting

We have unsafe references to remote devices that are notified to
disappear at lldd_dev_gone.  In order to clean this up we need a single
canonical source for device lookups and stable references once a lookup
succeeds.  Towards that end guarantee that domain_device.lldd_dev is
NULL as soon as we start the process of stopping a device.  Any code
path that wants to safely lookup a remote device must do so through
task->dev->lldd_dev (isci_lookup_device()).

For in-flight references outside of scic_lock we need reference counting
to ensure that the device is not recycled before we are done with it.
Simplify device back references to just scic_sds_request.target_device
which is now the only permissible internal reference that is maintained
relative to the reference count.

There were two occasions where we wanted new i/o's to be treated as
SAS_TASK_UNDELIVERED but where the domain_dev->lldd_dev link is still
intact.  Introduce a 'gone' flag to prevent i/o while waiting for libsas
to take action on the port down event.

One 'core' leftover is that we currently call
scic_remote_device_destruct() from isci_remote_device_deconstruct()
which is called when the 'core' says the device is stopped.  It would be
more natural for the final put to trigger
isci_remote_device_deconstruct() but this implementation is deferred as
it requires other changes.

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

1 files changed, 3 insertions, 6 deletions

diff --git a/drivers/scsi/isci/task.h b/drivers/scsi/isci/task.h
index d574a18956d7..42019de23805 100644
--- a/drivers/scsi/isci/task.h
+++ b/drivers/scsi/isci/task.h
@@ -213,18 +213,15 @@ int isci_bus_reset_handler(struct scsi_cmnd *cmd);
 
 void isci_task_build_tmf(
 	struct isci_tmf *tmf,
-	struct isci_remote_device *isci_device,
 	enum isci_tmf_function_codes code,
 	void (*tmf_sent_cb)(enum isci_tmf_cb_state,
 			    struct isci_tmf *,
 			    void *),
 	void *cb_data);
 
-
-int isci_task_execute_tmf(
-	struct isci_host *isci_host,
-	struct isci_tmf *tmf,
-	unsigned long timeout_ms);
+int isci_task_execute_tmf(struct isci_host *isci_host,
+			  struct isci_remote_device *idev,
+			  struct isci_tmf *tmf, unsigned long timeout_ms);
 
 /**
  * enum isci_completion_selection - This enum defines the possible actions to