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, 1 insertions, 2 deletions

diff --git a/drivers/scsi/isci/port.c b/drivers/scsi/isci/port.c
index fb66e30da..5f4a4e3 100644
--- a/drivers/scsi/isci/port.c
+++ b/drivers/scsi/isci/port.c
@@ -321,8 +321,7 @@ static void isci_port_link_down(struct isci_host *isci_host,
 				dev_dbg(&isci_host->pdev->dev,
 					"%s: isci_device = %p\n",
 					__func__, isci_device);
-				isci_remote_device_change_state(isci_device,
-								isci_stopping);
+				set_bit(IDEV_GONE, &isci_device->flags);
 			}
 		}
 		isci_port_change_state(isci_port, isci_stopping);