SCSI host lock push-down

Move the mid-layer's ->queuecommand() invocation from being locked
with the host lock to being unlocked to facilitate speeding up the
critical path for drivers who don't need this lock taken anyway.

The patch below presents a simple SCSI host lock push-down as an
equivalent transformation.  No locking or other behavior should change
with this patch.  All existing bugs and locking orders are preserved.

Additionally, add one parameter to queuecommand,
	struct Scsi_Host *
and remove one parameter from queuecommand,
	void (*done)(struct scsi_cmnd *)

Scsi_Host* is a convenient pointer that most host drivers need anyway,
and 'done' is redundant to struct scsi_cmnd->scsi_done.

Minimal code disturbance was attempted with this change.  Most drivers
needed only two one-line modifications for their host lock push-down.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
Acked-by: James Bottomley <James.Bottomley@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 6 insertions, 2 deletions

diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
index a688b1e686ea..689ee1fb702a 100644
--- a/drivers/usb/storage/scsiglue.c
+++ b/drivers/usb/storage/scsiglue.c
@@ -285,7 +285,7 @@ static int slave_configure(struct scsi_device *sdev)
 
 /* queue a command */
 /* This is always called with scsi_lock(host) held */
-static int queuecommand(struct scsi_cmnd *srb,
+static int queuecommand_lck(struct scsi_cmnd *srb,
                         void (*done)(struct scsi_cmnd *))
 {
         struct us_data *us = host_to_us(srb->device->host);
@@ -315,6 +315,8 @@ static int queuecommand(struct scsi_cmnd *srb,
         return 0;
 }
 
+static DEF_SCSI_QCMD(queuecommand)
+
 /***********************************************************************
  * Error handling functions
  ***********************************************************************/
diff --git a/drivers/usb/storage/uas.c b/drivers/usb/storage/uas.c
index d1268191acbd..339fac3949df 100644
--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -430,7 +430,7 @@ static int uas_submit_urbs(struct scsi_cmnd *cmnd,
         return 0;
 }
 
-static int uas_queuecommand(struct scsi_cmnd *cmnd,
+static int uas_queuecommand_lck(struct scsi_cmnd *cmnd,
                                         void (*done)(struct scsi_cmnd *))
 {
         struct scsi_device *sdev = cmnd->device;
@@ -488,6 +488,8 @@ static int uas_queuecommand(struct scsi_cmnd *cmnd,
         return 0;
 }
 
+static DEF_SCSI_QCMD(uas_queuecommand)
+
 static int uas_eh_abort_handler(struct scsi_cmnd *cmnd)
 {
         struct scsi_device *sdev = cmnd->device;