ocfs2: add first lock wait time in locking_state

ocfs2 file system uses locking_state file under debugfs to dump each
ocfs2 file system's dlm lock resources, but the users ever encountered
some hang(deadlock) problems in ocfs2 file system.  I'd like to add
first lock wait time in locking_state file, which can help the upper
scripts detect these deadlock problems via comparing the first lock wait
time with the current time.

Link: http://lkml.kernel.org/r/20190611015414.27754-3-ghe@suse.com
Signed-off-by: Gang He <ghe@suse.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Gang He <ghe@suse.com>
Cc: Jun Piao <piaojun@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/ocfs2.h

@@ -192,6 +192,7 @@ struct ocfs2_lock_res {
 #ifdef CONFIG_OCFS2_FS_STATS
 	struct ocfs2_lock_stats  l_lock_prmode;		/* PR mode stats */
 	u32                      l_lock_refresh;	/* Disk refreshes */
+	u64                      l_lock_wait;	/* First lock wait time */
 	struct ocfs2_lock_stats  l_lock_exmode;		/* EX mode stats */
 #endif
 #ifdef CONFIG_DEBUG_LOCK_ALLOC