xfs: add tracepoints to AGF/AGI read operations

To help track down AGI/AGF lock ordering issues, I added these
tracepoints to tell us when an AGI or AGF is read and locked.  With
these we can now determine if the lock ordering goes wrong from
tracing captures.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/fs/xfs/xfs_ialloc.c b/fs/xfs/xfs_ialloc.c
index 14d732f..e87719c 100644
--- a/fs/xfs/xfs_ialloc.c
+++ b/fs/xfs/xfs_ialloc.c
@@ -40,6 +40,7 @@
 #include "xfs_icreate_item.h"
 #include "xfs_icache.h"
 #include "xfs_dinode.h"
+#include "xfs_trace.h"
 
 
 /*
@@ -1627,8 +1628,9 @@
 {
 	int			error;
 
-	ASSERT(agno != NULLAGNUMBER);
+	trace_xfs_read_agi(mp, agno);
 
+	ASSERT(agno != NULLAGNUMBER);
 	error = xfs_trans_read_buf(mp, tp, mp->m_ddev_targp,
 			XFS_AG_DADDR(mp, agno, XFS_AGI_DADDR(mp)),
 			XFS_FSS_TO_BB(mp, 1), 0, bpp, &xfs_agi_buf_ops);
@@ -1651,6 +1653,8 @@
 	struct xfs_perag	*pag;	/* per allocation group data */
 	int			error;
 
+	trace_xfs_ialloc_read_agi(mp, agno);
+
 	error = xfs_read_agi(mp, tp, agno, bpp);
 	if (error)
 		return error;