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>

fs/xfs/xfs_alloc.c

@@ -2294,6 +2294,8 @@ xfs_read_agf(
 {
 	int		error;
 
+	trace_xfs_read_agf(mp, agno);
+
 	ASSERT(agno != NULLAGNUMBER);
 	error = xfs_trans_read_buf(
 			mp, tp, mp->m_ddev_targp,
@@ -2324,8 +2326,9 @@ xfs_alloc_read_agf(
 	struct xfs_perag	*pag;		/* per allocation group data */
 	int			error;
 
-	ASSERT(agno != NULLAGNUMBER);
+	trace_xfs_alloc_read_agf(mp, agno);
 
+	ASSERT(agno != NULLAGNUMBER);
 	error = xfs_read_agf(mp, tp, agno,
 			(flags & XFS_ALLOC_FLAG_TRYLOCK) ? XBF_TRYLOCK : 0,
 			bpp);

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 @@ xfs_read_agi(
 {
 	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 @@ xfs_ialloc_read_agi(
 	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;

fs/xfs/xfs_trace.h

@@ -135,6 +135,31 @@ DEFINE_PERAG_REF_EVENT(xfs_perag_clear_reclaim);
 DEFINE_PERAG_REF_EVENT(xfs_perag_set_eofblocks);
 DEFINE_PERAG_REF_EVENT(xfs_perag_clear_eofblocks);
 
+DECLARE_EVENT_CLASS(xfs_ag_class,
+	TP_PROTO(struct xfs_mount *mp, xfs_agnumber_t agno),
+	TP_ARGS(mp, agno),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(xfs_agnumber_t, agno)
+	),
+	TP_fast_assign(
+		__entry->dev = mp->m_super->s_dev;
+		__entry->agno = agno;
+	),
+	TP_printk("dev %d:%d agno %u",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __entry->agno)
+);
+#define DEFINE_AG_EVENT(name)	\
+DEFINE_EVENT(xfs_ag_class, name,	\
+	TP_PROTO(struct xfs_mount *mp, xfs_agnumber_t agno),	\
+	TP_ARGS(mp, agno))
+
+DEFINE_AG_EVENT(xfs_read_agf);
+DEFINE_AG_EVENT(xfs_alloc_read_agf);
+DEFINE_AG_EVENT(xfs_read_agi);
+DEFINE_AG_EVENT(xfs_ialloc_read_agi);
+
 TRACE_EVENT(xfs_attr_list_node_descend,
 	TP_PROTO(struct xfs_attr_list_context *ctx,
 		 struct xfs_da_node_entry *btree),