[XFS] replace the XFS buf iodone semaphore with a completion

The xfs_buf_t b_iodonesema is really just a semaphore that wants to be a
completion. Change it to a completion and remove the last user of the
sema_t from XFS.

SGI-PV: 981498

SGI-Modid: xfs-linux-melb:xfs-kern:31815a

Signed-off-by: David Chinner <david@fromorbit.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index a01daa7..a0072d9 100644
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -253,7 +253,7 @@
 
 	memset(bp, 0, sizeof(xfs_buf_t));
 	atomic_set(&bp->b_hold, 1);
-	init_MUTEX_LOCKED(&bp->b_iodonesema);
+	init_completion(&bp->b_iowait);
 	INIT_LIST_HEAD(&bp->b_list);
 	INIT_LIST_HEAD(&bp->b_hash_list);
 	init_MUTEX_LOCKED(&bp->b_sema); /* held, no waiters */
@@ -1033,7 +1033,7 @@
 			xfs_buf_iodone_work(&bp->b_iodone_work);
 		}
 	} else {
-		up(&bp->b_iodonesema);
+		complete(&bp->b_iowait);
 	}
 }
 
@@ -1271,7 +1271,7 @@
 	XB_TRACE(bp, "iowait", 0);
 	if (atomic_read(&bp->b_io_remaining))
 		blk_run_address_space(bp->b_target->bt_mapping);
-	down(&bp->b_iodonesema);
+	wait_for_completion(&bp->b_iowait);
 	XB_TRACE(bp, "iowaited", (long)bp->b_error);
 	return bp->b_error;
 }