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>

1 files changed, 21 insertions, 2 deletions

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index d0a6a845f204..e7e385842a38 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -127,8 +127,7 @@ struct scsi_host_template {
          *
          * STATUS: REQUIRED
          */
-        int (* queuecommand)(struct scsi_cmnd *,
-                             void (*done)(struct scsi_cmnd *));
+        int (* queuecommand)(struct Scsi_Host *, struct scsi_cmnd *);
 
         /*
          * The transfer functions are used to queue a scsi command to
@@ -505,6 +504,25 @@ struct scsi_host_template {
 };
 
 /*
+ * Temporary #define for host lock push down. Can be removed when all
+ * drivers have been updated to take advantage of unlocked
+ * queuecommand.
+ *
+ */
+#define DEF_SCSI_QCMD(func_name) \
+        int func_name(struct Scsi_Host *shost, struct scsi_cmnd *cmd)   \
+        {                                                               \
+                unsigned long irq_flags;                                \
+                int rc;                                                 \
+                spin_lock_irqsave(shost->host_lock, irq_flags);         \
+                scsi_cmd_get_serial(shost, cmd);                        \
+                rc = func_name##_lck (cmd, cmd->scsi_done);                     \
+                spin_unlock_irqrestore(shost->host_lock, irq_flags);    \
+                return rc;                                              \
+        }
+
+
+/*
  * shost state: If you alter this, you also need to alter scsi_sysfs.c
  * (for the ascii descriptions) and the state model enforcer:
  * scsi_host_set_state()
@@ -752,6 +770,7 @@ extern struct Scsi_Host *scsi_host_get(struct Scsi_Host *);
 extern void scsi_host_put(struct Scsi_Host *t);
 extern struct Scsi_Host *scsi_host_lookup(unsigned short);
 extern const char *scsi_host_state_name(enum scsi_host_state);
+extern void scsi_cmd_get_serial(struct Scsi_Host *, struct scsi_cmnd *);
 
 extern u64 scsi_calculate_bounce_limit(struct Scsi_Host *);