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, 2 insertions, 5 deletions

diff --git a/drivers/scsi/isci/request.h b/drivers/scsi/isci/request.h
index 8de2542f081f..9bb7c36257f3 100644
--- a/drivers/scsi/isci/request.h
+++ b/drivers/scsi/isci/request.h
@@ -285,7 +285,6 @@ struct isci_request {
                 struct isci_tmf *tmf_task_ptr;  /* When ttype==tmf_task */
         } ttype_ptr;
         struct isci_host *isci_host;
-        struct isci_remote_device *isci_device;
         /* For use in the requests_to_{complete|abort} lists: */
         struct list_head completed_node;
         /* For use in the reqs_in_process list: */
@@ -681,12 +680,10 @@ static inline void isci_request_free(struct isci_host *isci_host,
 
 struct isci_request *isci_request_alloc_tmf(struct isci_host *ihost,
                                             struct isci_tmf *isci_tmf,
-                                            struct isci_remote_device *idev,
                                             gfp_t gfp_flags);
 
-int isci_request_execute(struct isci_host *isci_host,
-                         struct sas_task *task,
-                         gfp_t gfp_flags);
+int isci_request_execute(struct isci_host *ihost, struct isci_remote_device *idev,
+                         struct sas_task *task, gfp_t gfp_flags);
 
 /**
  * isci_request_unmap_sgl() - This function unmaps the DMA address of a given